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Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

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  Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-25 19:10 +0100
    Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-11-26 02:00 +0100
    Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ben Hutchings <ben@decadent.org.uk> - 2016-11-29 02:20 +0100
      Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-11-29 03:40 +0100
        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-11-29 10:20 +0100
      Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 05:10 +0100
        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Adam Borowski <kilobyte@angband.pl> - 2016-11-29 14:20 +0100
          Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Ingo Molnar <mingo@kernel.org> - 2016-11-29 14:40 +0100
            Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Adam Borowski <kilobyte@angband.pl> - 2016-11-29 15:30 +0100
          [PATCH] x86/kbuild: enable modversions for symbols exported from asm Adam Borowski <kilobyte@angband.pl> - 2016-11-29 15:00 +0100
            Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 16:50 +0100
              Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-11-29 17:20 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 17:40 +0100
                  Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Ben Hutchings <ben@decadent.org.uk> - 2016-11-29 21:00 +0100
                    Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 22:00 +0100
                      Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-30 20:00 +0100
                        Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ben Hutchings <ben@decadent.org.uk> - 2016-11-30 22:40 +0100
                          Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-01 03:20 +0100
                            Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ben Hutchings <ben@decadent.org.uk> - 2016-12-01 03:40 +0100
                              Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-01 05:00 +0100
                                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-01 17:40 +0100
                                  Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-02 16:00 +0100
                                  Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-09 05:00 +0100
                                    Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Ian Campbell <ijc@hellion.org.uk> - 2016-12-09 16:30 +0100
                                      Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-09 17:40 +0100
                                        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-10 14:00 +0100
                        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-01 05:50 +0100
                          Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-01 05:50 +0100
                            Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-01 16:40 +0100
                              Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-01 17:00 +0100
                                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-01 17:40 +0100
                                  Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-01 20:10 +0100
                              Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Christoph Hellwig <hch@infradead.org> - 2016-12-01 17:10 +0100
                              Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-09 05:10 +0100
                                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-09 09:20 +0100
                                  Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-09 09:40 +0100
                                    Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-09 16:00 +0100
                                      Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-09 17:20 +0100
                                        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-09 17:30 +0100
                                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Don Zickus <dzickus@redhat.com> - 2016-12-09 17:40 +0100
                          Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-01 12:20 +0100
                            Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-01 12:30 +0100
                              Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Stanislav Kozina <skozina@redhat.com> - 2016-12-01 13:00 +0100
                                Re: [PATCH] x86/kbuild: enable modversions for symbols exported  from asm Nicholas Piggin <npiggin@gmail.com> - 2016-12-01 14:00 +0100
                              Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Dodji Seketeli <dodji@seketeli.org> - 2016-12-01 16:50 +0100
                          Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-01 17:40 +0100
              Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Adam Borowski <kilobyte@angband.pl> - 2016-11-29 18:10 +0100
                Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 18:30 +0100
                  Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-29 18:40 +0100
                    Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Arnd Bergmann <arnd@arndb.de> - 2016-12-01 15:20 +0100
                      Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-01 17:40 +0100
                      Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-01 19:50 +0100
                        Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Geert Uytterhoeven <geert@linux-m68k.org> - 2016-12-02 14:00 +0100
                          Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Arnd Bergmann <arnd@arndb.de> - 2016-12-02 16:10 +0100
                        Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Adam Borowski <kilobyte@angband.pl> - 2016-12-02 16:40 +0100
                        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-02 18:30 +0100
                        Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Ben Hutchings <ben@decadent.org.uk> - 2016-12-03 05:40 +0100
                          Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Arnd Bergmann <arnd@arndb.de> - 2016-12-03 12:10 +0100
                        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Alan Modra <amodra@gmail.com> - 2016-12-04 09:20 +0100
                          Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Linus Torvalds <torvalds@linux-foundation.org> - 2016-12-04 22:10 +0100
                  Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-11-29 22:50 +0100

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#1534270 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On 2016-12-01 04:39, Nicholas Piggin wrote:
> On Thu, 01 Dec 2016 02:35:54 +0000
> Ben Hutchings <ben@decadent.org.uk> wrote:
>> As I understand it, genksyms incorporates the definitions of a
>> function's parameter and return types - not just their names - and all
>> the types they refer to, recursively.  So a structure size change
>> should change the version of all functions where the function and its
>> caller pass that structure between them, however indirectly.  It finds
>> such indirect ABI breakage for me fairly regularly, though of course I
>> don't know that it finds everything.
> 
> It is only the type name.
> 
> Not only that but even if you did extend it further to structure type
> arrangement then you still have to deal with other structures followed
> via pointers. Or (rarer but not unheard of):
> 
> - changes to structures without changes of the types of their members
> - changes to arguments without changes of their type

This is already covered by genksyms. Try make V=1 with
CONFIG_MODVERSIONS=y and add the -D option to one of the genksyms
command. I wanted to paste the expanded signature for
register_filesystem() as an example, but vger would probably drop the
mail for being too big :).


> - changes to semantics of functions
> - data structures derived in ways other than exported symbols, e.g.,
>   fixed register for `current` on some archs

Right, this is something that genksyms has no idea about.

Michal

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#1534998 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On 01.12.2016 17:12, Michal Marek wrote:
> On 2016-12-01 04:39, Nicholas Piggin wrote:
>> On Thu, 01 Dec 2016 02:35:54 +0000
>> Ben Hutchings <ben@decadent.org.uk> wrote:
>>> As I understand it, genksyms incorporates the definitions of a
>>> function's parameter and return types - not just their names - and all
>>> the types they refer to, recursively.  So a structure size change
>>> should change the version of all functions where the function and its
>>> caller pass that structure between them, however indirectly.  It finds
>>> such indirect ABI breakage for me fairly regularly, though of course I
>>> don't know that it finds everything.
>>
>> It is only the type name.
>>
>> Not only that but even if you did extend it further to structure type
>> arrangement then you still have to deal with other structures followed
>> via pointers. Or (rarer but not unheard of):
>>
>> - changes to structures without changes of the types of their members
>> - changes to arguments without changes of their type
> 
> This is already covered by genksyms. Try make V=1 with
> CONFIG_MODVERSIONS=y and add the -D option to one of the genksyms
> command. I wanted to paste the expanded signature for
> register_filesystem() as an example, but vger would probably drop the
> mail for being too big :).

It is easier to just use e.g. `make net/core/dev.symtypes` and look at
the generated file.

Bye,
Hannes

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#1539054 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Thu, 1 Dec 2016 17:12:41 +0100
Michal Marek <mmarek@suse.com> wrote:

> On 2016-12-01 04:39, Nicholas Piggin wrote:
> > On Thu, 01 Dec 2016 02:35:54 +0000
> > Ben Hutchings <ben@decadent.org.uk> wrote:  
> >> As I understand it, genksyms incorporates the definitions of a
> >> function's parameter and return types - not just their names - and all
> >> the types they refer to, recursively.  So a structure size change
> >> should change the version of all functions where the function and its
> >> caller pass that structure between them, however indirectly.  It finds
> >> such indirect ABI breakage for me fairly regularly, though of course I
> >> don't know that it finds everything.  
> > 
> > It is only the type name.
> > 
> > Not only that but even if you did extend it further to structure type
> > arrangement then you still have to deal with other structures followed
> > via pointers. Or (rarer but not unheard of):
> > 
> > - changes to structures without changes of the types of their members
> > - changes to arguments without changes of their type  
> 
> This is already covered by genksyms. Try make V=1 with
> CONFIG_MODVERSIONS=y and add the -D option to one of the genksyms
> command. I wanted to paste the expanded signature for
> register_filesystem() as an example, but vger would probably drop the
> mail for being too big :).

Well I simply tested the outcome. If you have:

struct blah {
  int x;
};
int foo(struct blah *blah)
{
  return blah->x;
}
EXPORT(foo);

$ nm vmlinux | grep __crc_foo
00000000a0cf13a0 A __crc_foo

Now change to

struct blah {
  int y;
  int x;
};

$ nm vmlinux | grep __crc_foo
00000000a0cf13a0 A __crc_foo

It just doesn't catch these things. Honestly, stable ABI distros *have*
to review all patches to ensure the ABI is unchanged. Some tools could
help significantly, but for that, the debug info ABI checking tools that
have been mentioned in this thread are far better tool for this job than
modversions.

Thanks,
Nick

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#1539441 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Fri, 2016-12-09 at 13:33 +1000, Nicholas Piggin wrote:
> 
> Well I simply tested the outcome. If you have:
> 
> struct blah {
>   int x;
> };
> int foo(struct blah *blah)
> {
>   return blah->x;
> }
> EXPORT(foo);
> 
> $ nm vmlinux | grep __crc_foo
> 00000000a0cf13a0 A __crc_foo
> 
> Now change to
> 
> struct blah {
>   int y;
>   int x;
> };
> 
> $ nm vmlinux | grep __crc_foo
> 00000000a0cf13a0 A __crc_foo
> 
> It just doesn't catch these things.

I found the same when I just added your snippet to init/main.c.

_But_ when I moved the struct into include/types.h (which happened to
be included by init/main.c) then, with just x in the struct:

    $ make -s init/main.{o,symtypes} && grep -E foo\|blah init/main.symtypes && nm init/main.o  | grep __crc_foo
    s#blah struct blah { int x ; } 
    foo int foo ( s#blah * ) 
    000000000cd0312e A __crc_foo

but adding y:

    $ make -s init/main.{o,symtypes} && grep -E foo\|blah init/main.symtypes && nm init/main.o  | grep __crc_foo
    s#blah struct blah { int x ; int y ; } 
    foo int foo ( s#blah * ) 
    00000000eda220c6 A __crc_foo

So it does catch things in that case.

With struct blah inline in main.c it was:

    $ make -s init/main.{o,symtypes} && grep -E foo\|blah init/main.symtypes && nm init/main.o  | grep __crc_foo
    s#blah struct blah { UNKNOWN } 
    foo int foo ( s#blah * ) 
    00000000a0cf13a0 A __crc_foo

So I suppose it only cares about structs which are in headers, which I
guess makes sense. I think it is working in at least one of the
important cases.

Ian.

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#1539546 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Fri, 09 Dec 2016 15:21:33 +0000
Ian Campbell <ijc@hellion.org.uk> wrote:

> On Fri, 2016-12-09 at 13:33 +1000, Nicholas Piggin wrote:
> > 
> > Well I simply tested the outcome. If you have:
> > 
> > struct blah {
> >   int x;
> > };
> > int foo(struct blah *blah)
> > {
> >   return blah->x;
> > }
> > EXPORT(foo);
> > 
> > $ nm vmlinux | grep __crc_foo
> > 00000000a0cf13a0 A __crc_foo
> > 
> > Now change to
> > 
> > struct blah {
> >   int y;
> >   int x;
> > };
> > 
> > $ nm vmlinux | grep __crc_foo
> > 00000000a0cf13a0 A __crc_foo
> > 
> > It just doesn't catch these things.  
> 
> I found the same when I just added your snippet to init/main.c.
> 
> _But_ when I moved the struct into include/types.h (which happened to
> be included by init/main.c) then, with just x in the struct:
> 
>     $ make -s init/main.{o,symtypes} && grep -E foo\|blah init/main.symtypes && nm init/main.o  | grep __crc_foo
>     s#blah struct blah { int x ; } 
>     foo int foo ( s#blah * ) 
>     000000000cd0312e A __crc_foo
> 
> but adding y:
> 
>     $ make -s init/main.{o,symtypes} && grep -E foo\|blah init/main.symtypes && nm init/main.o  | grep __crc_foo
>     s#blah struct blah { int x ; int y ; } 
>     foo int foo ( s#blah * ) 
>     00000000eda220c6 A __crc_foo
> 
> So it does catch things in that case.
> 
> With struct blah inline in main.c it was:
> 
>     $ make -s init/main.{o,symtypes} && grep -E foo\|blah init/main.symtypes && nm init/main.o  | grep __crc_foo
>     s#blah struct blah { UNKNOWN } 
>     foo int foo ( s#blah * ) 
>     00000000a0cf13a0 A __crc_foo
> 
> So I suppose it only cares about structs which are in headers, which I
> guess makes sense. I think it is working in at least one of the
> important cases.

Aha thanks, well that's my mistake. Clever little bugger, isn't it? Okay
it's not so useless as I first thought!

That said, a dwarf based checker tool should be able to do as good a job
(maybe a bit better because report is very informative and it may pick up
compiler alignments or padding options). So I still think it's worth
looking at those if we can remove modversions.

Thanks,
Nick

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#1539830 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Fri, Dec 09, 2016 at 11:46:54PM +0100, Dodji Seketeli wrote:
> Hello,
> 
> Nicholas Piggin <npiggin@gmail.com> a écrit:
> 
> [...]
> 
> > That said, a dwarf based checker tool should be able to do as good a job
> > (maybe a bit better because report is very informative and it may pick up
> > compiler alignments or padding options).
> 
> So, Nicholas was kind enough to send me the two Linux Kernel binaries
> that he built with the tiny little interface change that we were
> discussing earlier.  Here is what the abidiff[1] tools says about that
> interface change:
> 
>     $ time ~/git/libabigail/kabidiff/build/tools/abidiff vmlinux.abi1.abi vmlinux.abi2.abi
>     Functions changes summary: 0 Removed, 1 Changed, 0 Added function
>     Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
> 
>     1 function with some indirect sub-type change:
> 
>       [C]'function int foo(blah*)' at memory.c:82:1 has some indirect sub-type changes:
>         parameter 1 of type 'blah*' has sub-type changes:
>           in pointed to type 'struct blah' at memory.c:78:1:
>             type size changed from 32 to 64 bits
>             1 data member insertion:
>               'int blah::y', at offset 0 (in bits) at memory.c:79:1
>             1 data member change:
>              'int blah::x' offset changed from 0 to 32 (in bits) (by +32 bits)
> 
> 
> 
>     real	0m2.595s
>     user	0m2.489s
>     sys	0m0.108s
>     $ 
> 
> I kept the timing information to give you an idea of the time it takes
> on a non-optimized build of abidiff.
> 
> One could for instance want that types that are not defined in header
> files be kept out of the change report.  In that case it's possible to
> write a little suppression specification file like this one:
> 
>     $ cat vmlinux.abignore 
>     [suppress_type]
>       source_location_not_regexp = .*\\.h
>     $
> 
> You can then pass that suppression file to the tool:
> 
>     $ ~/git/libabigail/kabidiff/build/tools/abidiff --suppr vmlinux.abignore vmlinux.abi1.abi vmlinux.abi2.abi
>     Functions changes summary: 0 Removed, 0 Changed (1 filtered out), 0 Added function
>     Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
> 
> 
>     real	0m2.574s
>     user	0m2.473s
>     sys	0m0.102s
>     $
> 
> So this is the kind of interface change analysis tool we are working on
> at the moment.
> 
> One could also imagine a tool that would compute a CRC that takes the
> very same suppression specification files into account, letting people
> to decide that some interface changes are OK.  That CRC would thus be
> added to the special ELF sections we already have today.  We could keep
> the modversion machinery, but with a greater dose of flexibility.
> Whenever modversion detects a change, abidiff would tell people what the
> change is exactly.
> 
> What do you guys think?

YES YES YES!!!

Now I don't work on a distro anymore, but I would think that something
like this would be really useful, pointing out exactly what changed is
very important for distro maintainers to determine what they want to do
(either fix up the abi change with strange hacks, or ignore it due to
the change being in an area they don't care at all about, i.e. a random
driver subsystem.)

So yes, I think this is really good stuff.  But if the distro
maintainers correct me and think it's useless, then I need to revisit my
view of exactly what they do for their customers :)

thanks,

greg k-h

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#1533796 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Wed, Nov 30, 2016 at 10:40:02AM -0800, Linus Torvalds wrote:
> On Wed, Nov 30, 2016 at 10:18 AM, Nicholas Piggin <npiggin@gmail.com> wrote:
> >
> > Here's an initial rough hack at removing modversions. It gives an idea
> > of the complexity we're carrying for this feature (keeping in mind most
> > of the lines removed are generated parser).
> 
> You definitely don't have to try to convince me. We've had many issues
> with modversions over the years. This was just the "last drop" as far
> as I'm concerned, we've had random odd crc generation failures due to
> some build races too.
> 
> > In its place I just added a simple config option to override vermagic
> > so distros can manage it entirely themselves.
> 
> So at least Fedora doesn't even enable CONFIG_MODVERSIONS as-is. I'm
> _hoping_ it's just Debian that wants this, and we'd need to get some
> input from the Debian people whether that "control vermagic" is
> sufficient? I suspect it isn't, but I can't come up with any simple
> alternate model either..

Oddly, I just posted a patch to enable this for Fedora and then someone
pointed me at this thread. :-/

Sorry for chiming in late, but yes RHEL is a big user of MODVERSIONS for our
kabi protection work.  Despite our best intentions we still have lots of
partners and customers that provide value-add out-of-tree drivers to their
customers.  These module builders requested we have a mechanism to allow
rolling modules forward for each of our minor RHEL updates without breaking
their drivers.

They requested this to save time and money on rebuilding and retesting.  It
also helps deal with situations where RHEL puts out a security fix or new
minor release and the provider of OOT driver has not released the
appropriate update.  Customers like the ability to roll their special
drivers forward quickly to their schedule.

Now we don't protect every symbol, just a select few that our meets our
customers needs (and developers willing to support it).

Anyway, MODVERSIONS is our way of protecting our kabi for the last 10 years.
It isn't perfect and we have fixed the genksyms tool over the years, but so
far it mostly works fine.

I am not sure what 'control vermagic' is, but it sounds like a string check,
which won't protect against the boatload of backports we do to structs,
enums, and functions.

Currently we are exploring various ways to get smarter here.  The genksyms
tool has its limitations and handling kabi hacks in RHEL is getting
tiresome.

I think GregKH pointed to one such tool, libabigail?  We are working on
others too.


Circling back to enabling MODVERSIONS in Fedora, that was to start the
process of syncing Fedora with RHEL stuff in preparation for smarter tools.


If you take away MODVERSIONS, that would put a damper in our work, but
easily carried privately (much like MODSIGNING for 8 years until it went
upstream :-) ).


We would prefer to work with various folks to figure out a better solution
to solve our/others needs.  Anyone interested in working with Red Hat should
contact Stanislav Kozina (skozina@redhat.com) (cc'd above) and cc myself.

Cheers,
Don



> 
> I'm also somewhat surprised that it's Debian that has this problem,
> considering how Debian is usually the distro that is _least_ receptive
> to various non-free binaries.
> 
>             Linus

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#1533798 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Wed, 30 Nov 2016 23:13:25 -0500
Don Zickus <dzickus@redhat.com> wrote:

> On Wed, Nov 30, 2016 at 10:40:02AM -0800, Linus Torvalds wrote:
> > On Wed, Nov 30, 2016 at 10:18 AM, Nicholas Piggin <npiggin@gmail.com> wrote:  
> > >
> > > Here's an initial rough hack at removing modversions. It gives an idea
> > > of the complexity we're carrying for this feature (keeping in mind most
> > > of the lines removed are generated parser).  
> > 
> > You definitely don't have to try to convince me. We've had many issues
> > with modversions over the years. This was just the "last drop" as far
> > as I'm concerned, we've had random odd crc generation failures due to
> > some build races too.
> >   
> > > In its place I just added a simple config option to override vermagic
> > > so distros can manage it entirely themselves.  
> > 
> > So at least Fedora doesn't even enable CONFIG_MODVERSIONS as-is. I'm
> > _hoping_ it's just Debian that wants this, and we'd need to get some
> > input from the Debian people whether that "control vermagic" is
> > sufficient? I suspect it isn't, but I can't come up with any simple
> > alternate model either..  
> 
> Oddly, I just posted a patch to enable this for Fedora and then someone
> pointed me at this thread. :-/
> 
> Sorry for chiming in late, but yes RHEL is a big user of MODVERSIONS for our
> kabi protection work.  Despite our best intentions we still have lots of
> partners and customers that provide value-add out-of-tree drivers to their
> customers.  These module builders requested we have a mechanism to allow
> rolling modules forward for each of our minor RHEL updates without breaking
> their drivers.
> 
> They requested this to save time and money on rebuilding and retesting.  It
> also helps deal with situations where RHEL puts out a security fix or new
> minor release and the provider of OOT driver has not released the
> appropriate update.  Customers like the ability to roll their special
> drivers forward quickly to their schedule.
> 
> Now we don't protect every symbol, just a select few that our meets our
> customers needs (and developers willing to support it).
> 
> Anyway, MODVERSIONS is our way of protecting our kabi for the last 10 years.
> It isn't perfect and we have fixed the genksyms tool over the years, but so
> far it mostly works fine.

Okay. It would be good to get all the distros in on this.

What I want to do is work out exactly what it is that modversions is
giving you.

We know it's fairly nasty code to maintain and it does not detect ABI
changes very well. But it's not such a burden that we can't maintain
it if there are good reasons to keep it.

> I am not sure what 'control vermagic' is, but it sounds like a string check,
> which won't protect against the boatload of backports we do to structs,
> enums, and functions.

Basically vermagic is the string all modules and the kernel get, which
must match in order to load modules. If you have modversions disabled,
then vermagic includes the kernel version. If modversions is enabled,
then vermagic does not include the kernel version but the CRCs have to
also match.

Controlling it explicitly is just a couple of lines where a distro can
control it (so they can update their kernel version without breaking).
It's not meant to solve everything, just the first one.
 
> Currently we are exploring various ways to get smarter here.  The genksyms
> tool has its limitations and handling kabi hacks in RHEL is getting
> tiresome.
> 
> I think GregKH pointed to one such tool, libabigail?  We are working on
> others too.
> 
> 
> Circling back to enabling MODVERSIONS in Fedora, that was to start the
> process of syncing Fedora with RHEL stuff in preparation for smarter tools.
> 
> 
> If you take away MODVERSIONS, that would put a damper in our work, but
> easily carried privately (much like MODSIGNING for 8 years until it went
> upstream :-) ).

I don't think that's necessary. A feature requirement for a distro is just
as valid as any other user of upstream. I don't want to hinder any distro,
I'm just still not quite seeing the big picture of exactly what functionality
you need from the kernel.

Thanks,
Nick

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#1534201 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Thu, Dec 01, 2016 at 03:32:15PM +1100, Nicholas Piggin wrote:
> > Anyway, MODVERSIONS is our way of protecting our kabi for the last 10 years.
> > It isn't perfect and we have fixed the genksyms tool over the years, but so
> > far it mostly works fine.
> 
> Okay. It would be good to get all the distros in on this.
> 
> What I want to do is work out exactly what it is that modversions is
> giving you.
> 
> We know it's fairly nasty code to maintain and it does not detect ABI
> changes very well. But it's not such a burden that we can't maintain
> it if there are good reasons to keep it.

Hi Nick,

I won't disagree with you there. :-)

modversions is a pretty heavy handed approach that basically says if all the
symbols and types haven't changed for a given EXPORT_SYMBOL (recursively
checked), then there is a high degree of confidence the OOT driver will not
only load, but run correctly.

The question is how to provide a similar guarantee if a different way?

We have plenty of customers with 10 year old drivers, where the expertise
has long left the company.  The engineers still around, recompile and make
tweaks to get things working on the latest RHEL.  Verify it passes testing
and release it.  Then they hope to not touch it again for a few years until
the next RHEL comes along.

Scary, huh? :-)

Common examples, filesystems and storage drivers.


There is no way that I see to provide a 100% guarantee, but if we do enough
checks, we should be able to have a high degree of confidence the driver
won't blow up.

On the flip side, easy things in the kernel to do is:

- provide the memory allocation (instead of having the driver staticly
  allocate)
- provide functions to retrieve various internal data (instead of having the
  driver do direct referencing to deep internal elements)
- cut down on some static inlines (and use accessory functions instead),
  etc.

Those types of changes allow the OOT driver to be more ignorant of kernel
changes and struct modifications.


Look to Stanislav's responses for his ideas on new tooling.

Thanks for helping!

Cheers,
Don


> 
> > I am not sure what 'control vermagic' is, but it sounds like a string check,
> > which won't protect against the boatload of backports we do to structs,
> > enums, and functions.
> 
> Basically vermagic is the string all modules and the kernel get, which
> must match in order to load modules. If you have modversions disabled,
> then vermagic includes the kernel version. If modversions is enabled,
> then vermagic does not include the kernel version but the CRCs have to
> also match.
> 
> Controlling it explicitly is just a couple of lines where a distro can
> control it (so they can update their kernel version without breaking).
> It's not meant to solve everything, just the first one.
>  
> > Currently we are exploring various ways to get smarter here.  The genksyms
> > tool has its limitations and handling kabi hacks in RHEL is getting
> > tiresome.
> > 
> > I think GregKH pointed to one such tool, libabigail?  We are working on
> > others too.
> > 
> > 
> > Circling back to enabling MODVERSIONS in Fedora, that was to start the
> > process of syncing Fedora with RHEL stuff in preparation for smarter tools.
> > 
> > 
> > If you take away MODVERSIONS, that would put a damper in our work, but
> > easily carried privately (much like MODSIGNING for 8 years until it went
> > upstream :-) ).
> 
> I don't think that's necessary. A feature requirement for a distro is just
> as valid as any other user of upstream. I don't want to hinder any distro,
> I'm just still not quite seeing the big picture of exactly what functionality
> you need from the kernel.
> 
> Thanks,
> Nick

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#1534231 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Thu, Dec 01, 2016 at 07:26:09AM -0800, Christoph Hellwig wrote:
> On Thu, Dec 01, 2016 at 10:20:39AM -0500, Don Zickus wrote:
> > 
> > - provide the memory allocation (instead of having the driver staticly
> >   allocate)
> > - provide functions to retrieve various internal data (instead of having the
> >   driver do direct referencing to deep internal elements)
> > - cut down on some static inlines (and use accessory functions instead),
> >   etc.
> > 
> > Those types of changes allow the OOT driver to be more ignorant of kernel
> > changes and struct modifications.
> 
> All that is counter to what we really want to have:  a well integrated
> kernel that moves forward together so that we can see and improve the
> whole situation.  No need to make things worse just to help leeches.
> Get your damn drivers upstream ASAP and let's stop this discussion..

I understand and won't disagree with you. :-)

Unfortunately, there are various drivers that will never go upstream

- paid storage drivers that provide bells and whistles on top of inbox
  driver
- old drivers/fs that application has been relying on for a long time but
  company doesn't have resources to migrate to current technology.

We have been trying over the years to do what we can to move customers in
the right direction.  It is just a slow process, sadly.

Cheers,
Don

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#1534272 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Thu, Dec 01, 2016 at 10:40:59AM -0500, Don Zickus wrote:
> Unfortunately, there are various drivers that will never go upstream
> 
> - paid storage drivers that provide bells and whistles on top of inbox
>   driver

That's because the developer doesn't want them upstream, that's their
fault, nothing we can do about them.

> - old drivers/fs that application has been relying on for a long time but
>   company doesn't have resources to migrate to current technology.

That's what drivers/staging/ is for, I'll take anything that builds (and
sometimes stuff that doesn't build) as long as people are actually using
it.  So send the stuff that is in this category on to me and that will
reduce your burden a _lot_.

thanks,

greg k-h

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#1534387 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Thu, Dec 01, 2016 at 05:06:11PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Dec 01, 2016 at 10:40:59AM -0500, Don Zickus wrote:
> > Unfortunately, there are various drivers that will never go upstream
> > 
> > - paid storage drivers that provide bells and whistles on top of inbox
> >   driver
> 
> That's because the developer doesn't want them upstream, that's their
> fault, nothing we can do about them.
> 
> > - old drivers/fs that application has been relying on for a long time but
> >   company doesn't have resources to migrate to current technology.
> 
> That's what drivers/staging/ is for, I'll take anything that builds (and
> sometimes stuff that doesn't build) as long as people are actually using
> it.  So send the stuff that is in this category on to me and that will
> reduce your burden a _lot_.

Hi Greg,

I will forward this offer to the right folks and see who we can get to bite.
:-)  Thanks!

Cheers,
Don

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#1534235 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Thu, Dec 01, 2016 at 10:20:39AM -0500, Don Zickus wrote:
> 
> - provide the memory allocation (instead of having the driver staticly
>   allocate)
> - provide functions to retrieve various internal data (instead of having the
>   driver do direct referencing to deep internal elements)
> - cut down on some static inlines (and use accessory functions instead),
>   etc.
> 
> Those types of changes allow the OOT driver to be more ignorant of kernel
> changes and struct modifications.

All that is counter to what we really want to have:  a well integrated
kernel that moves forward together so that we can see and improve the
whole situation.  No need to make things worse just to help leeches.
Get your damn drivers upstream ASAP and let's stop this discussion..

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#1539058 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Thu, 1 Dec 2016 10:20:39 -0500
Don Zickus <dzickus@redhat.com> wrote:

> On Thu, Dec 01, 2016 at 03:32:15PM +1100, Nicholas Piggin wrote:
> > > Anyway, MODVERSIONS is our way of protecting our kabi for the last 10 years.
> > > It isn't perfect and we have fixed the genksyms tool over the years, but so
> > > far it mostly works fine.  
> > 
> > Okay. It would be good to get all the distros in on this.
> > 
> > What I want to do is work out exactly what it is that modversions is
> > giving you.
> > 
> > We know it's fairly nasty code to maintain and it does not detect ABI
> > changes very well. But it's not such a burden that we can't maintain
> > it if there are good reasons to keep it.  
> 
> Hi Nick,
> 
> I won't disagree with you there. :-)

Sorry for the late reply, I was moving house and got side tracked.

> modversions is a pretty heavy handed approach that basically says if all the
> symbols and types haven't changed for a given EXPORT_SYMBOL (recursively
> checked), then there is a high degree of confidence the OOT driver will not
> only load, but run correctly.

It's heavy handed in that it is quite complex in the kernel build system,
but it is also light handed in that it does not do a very good job.

I would say the degree of confidence is not very high. People have told
me modversions follows pointers to objects in its calculation, but I have
not seen that to be the case. Even if you did have that, it can not replace
a code review for semantics of data and code.

> The question is how to provide a similar guarantee if a different way?

As a tool to aid distro reviewers, modversions has some value, but the
debug info parsing tools that have been mentioned in this thread seem
superior (not that I've tested them).

> 
> We have plenty of customers with 10 year old drivers, where the expertise
> has long left the company.  The engineers still around, recompile and make
> tweaks to get things working on the latest RHEL.  Verify it passes testing
> and release it.  Then they hope to not touch it again for a few years until
> the next RHEL comes along.
> 
> Scary, huh? :-)

Oh yeah my aim here is not to make distro or out of tree module vendors
life harder, actually the opposite. If it turns out modversions really is
the best approach, I'm not in a position to complain about its complexity
because we have Suse and Redhat people maintaining the build and module
systems :) I just want to see if we can do things better.

Thanks,
Nick

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#1539175 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

>> The question is how to provide a similar guarantee if a different way?
> As a tool to aid distro reviewers, modversions has some value, but the
> debug info parsing tools that have been mentioned in this thread seem
> superior (not that I've tested them).

On the other hand the big advantage of modversions is that it also 
verifies the checksum during runtime (module loading). In other words, I 
believe that any other solution should still generate some form of 
checksum/watermark which can be easily checked for compatibility on 
module load.
It should not be hard to add to the DWARF based tools though. We'd just 
parse DWARF data instead of the C code.

Regards,
-Stanislav

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#1539188 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Fri, 9 Dec 2016 08:55:51 +0100
Stanislav Kozina <skozina@redhat.com> wrote:

> >> The question is how to provide a similar guarantee if a different way?  
> > As a tool to aid distro reviewers, modversions has some value, but the
> > debug info parsing tools that have been mentioned in this thread seem
> > superior (not that I've tested them).  
> 
> On the other hand the big advantage of modversions is that it also 
> verifies the checksum during runtime (module loading). In other words, I 
> believe that any other solution should still generate some form of 
> checksum/watermark which can be easily checked for compatibility on 
> module load.
> It should not be hard to add to the DWARF based tools though. We'd just 
> parse DWARF data instead of the C code.

A runtime check is still done, with per-module vermagic which distros
can change when they bump the ABI version. Is it really necessary to
have more than that (i.e., per-symbol versioning)?

Thanks,
Nick

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#1539423 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

>>>> The question is how to provide a similar guarantee if a different way?
>>> As a tool to aid distro reviewers, modversions has some value, but the
>>> debug info parsing tools that have been mentioned in this thread seem
>>> superior (not that I've tested them).
>> On the other hand the big advantage of modversions is that it also
>> verifies the checksum during runtime (module loading). In other words, I
>> believe that any other solution should still generate some form of
>> checksum/watermark which can be easily checked for compatibility on
>> module load.
>> It should not be hard to add to the DWARF based tools though. We'd just
>> parse DWARF data instead of the C code.
> A runtime check is still done, with per-module vermagic which distros
> can change when they bump the ABI version. Is it really necessary to
> have more than that (i.e., per-symbol versioning)?

 From my point of view, it is. We need to allow changing ABI for some 
modules while maintaining it for others.
In fact I think that there should be version not only for every exported 
symbol (in the EXPORT_SYMBOL() sense), but also for every public type 
(in the sense of eg. structure defined in the public header file).

Thanks,
-Stanislav

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#1539477 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Fri, 9 Dec 2016 15:36:04 +0100
Stanislav Kozina <skozina@redhat.com> wrote:

> >>>> The question is how to provide a similar guarantee if a different way?  
> >>> As a tool to aid distro reviewers, modversions has some value, but the
> >>> debug info parsing tools that have been mentioned in this thread seem
> >>> superior (not that I've tested them).  
> >> On the other hand the big advantage of modversions is that it also
> >> verifies the checksum during runtime (module loading). In other words, I
> >> believe that any other solution should still generate some form of
> >> checksum/watermark which can be easily checked for compatibility on
> >> module load.
> >> It should not be hard to add to the DWARF based tools though. We'd just
> >> parse DWARF data instead of the C code.  
> > A runtime check is still done, with per-module vermagic which distros
> > can change when they bump the ABI version. Is it really necessary to
> > have more than that (i.e., per-symbol versioning)?  
> 
>  From my point of view, it is. We need to allow changing ABI for some 
> modules while maintaining it for others.
> In fact I think that there should be version not only for every exported 
> symbol (in the EXPORT_SYMBOL() sense), but also for every public type 
> (in the sense of eg. structure defined in the public header file).

Well the distro can just append _v2, _v3 to the name of the function
or type if it has to break compat for some reason. Would that be enough?

Thanks,
Nick

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#1539531 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Sat, Dec 10, 2016 at 01:56:53AM +1000, Nicholas Piggin wrote:
> On Fri, 9 Dec 2016 15:36:04 +0100
> Stanislav Kozina <skozina@redhat.com> wrote:
> 
> > >>>> The question is how to provide a similar guarantee if a different way?  
> > >>> As a tool to aid distro reviewers, modversions has some value, but the
> > >>> debug info parsing tools that have been mentioned in this thread seem
> > >>> superior (not that I've tested them).  
> > >> On the other hand the big advantage of modversions is that it also
> > >> verifies the checksum during runtime (module loading). In other words, I
> > >> believe that any other solution should still generate some form of
> > >> checksum/watermark which can be easily checked for compatibility on
> > >> module load.
> > >> It should not be hard to add to the DWARF based tools though. We'd just
> > >> parse DWARF data instead of the C code.  
> > > A runtime check is still done, with per-module vermagic which distros
> > > can change when they bump the ABI version. Is it really necessary to
> > > have more than that (i.e., per-symbol versioning)?  
> > 
> >  From my point of view, it is. We need to allow changing ABI for some 
> > modules while maintaining it for others.
> > In fact I think that there should be version not only for every exported 
> > symbol (in the EXPORT_SYMBOL() sense), but also for every public type 
> > (in the sense of eg. structure defined in the public header file).
> 
> Well the distro can just append _v2, _v3 to the name of the function
> or type if it has to break compat for some reason. Would that be enough?

There are other ways that distros can work around when upstream "breaks"
the ABI, sometimes they can rename functions, and others they can
"preload" structures with padding in anticipation for when/if fields get
added to them.  But that's all up to the distros, no need for us to
worry about that at all :)

thanks,

greg k-h

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#1539535 — Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

On Fri, Dec 09, 2016 at 01:50:41PM +1000, Nicholas Piggin wrote:
> > 
> > We have plenty of customers with 10 year old drivers, where the expertise
> > has long left the company.  The engineers still around, recompile and make
> > tweaks to get things working on the latest RHEL.  Verify it passes testing
> > and release it.  Then they hope to not touch it again for a few years until
> > the next RHEL comes along.
> > 
> > Scary, huh? :-)
> 
> Oh yeah my aim here is not to make distro or out of tree module vendors
> life harder, actually the opposite. If it turns out modversions really is
> the best approach, I'm not in a position to complain about its complexity
> because we have Suse and Redhat people maintaining the build and module
> systems :) I just want to see if we can do things better.

Hi Nick,

I think we are in pretty good agreement here.  We can do better than
modversions.  On the flip side, I would hate to see modversions ripped out
until we have an alternate path forward as it does get us by for now. :-)

Cheers,
Don

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