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Groups > linux.kernel > #1470413
| From | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc |
| Date | 2016-08-25 23:00 +0200 |
| Message-ID | <sa9UK-619-13@gated-at.bofh.it> (permalink) |
| References | <s9mqZ-6hm-5@gated-at.bofh.it> <s9pyx-8gG-1@gated-at.bofh.it> <s9xmp-50I-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Tue, Aug 23, 2016 at 10:37:43PM -0400, Kees Cook wrote:
> On Tue, Aug 23, 2016 at 3:28 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > This is a revert of:
> >
> > 2fb0815c9ee6 ("gcc4: disable __compiletime_object_size for GCC 4.6+")
> >
> > The goal of that commit was to silence the "provably correct" gcc
> > warnings. But it went too far: it also disabled the runtime warnings.
> >
> > Now that the pretty much useless gcc warnings have been properly
> > disposed of with the previous patch, re-enable this checking on modern
> > versions of gcc so we can get the runtime warnings again.
>
> As far as I know, this will still be broken since it's
> __builtin_object_size() that is buggy. Maybe I'm misunderstanding
> which piece is busted, though?
What specifically is buggy with __builtin_object_size()? Looking at the
generated code for a few of the "provably correct" warning sites, the
values generated by __builtin_object_size() are correct.
I think the problem is really related to the compile-time warning
function attribute used by __copy_to_user_overflow(). The warning is
printed when gcc *can* determine the object size but it *can't*
determine the copy size. The warning just means that, even though the
object has a const size, gcc isn't able to prove that the overflow won't
happen.
As an example, here's one of the warnings:
In file included from /home/jpoimboe/git/linux/include/linux/uaccess.h:5:0,
from /home/jpoimboe/git/linux/arch/x86/include/asm/stacktrace.h:9,
from /home/jpoimboe/git/linux/arch/x86/include/asm/perf_event.h:246,
from /home/jpoimboe/git/linux/include/linux/perf_event.h:24,
from /home/jpoimboe/git/linux/kernel/sys.c:16:
In function ‘copy_to_user.part.10’,
inlined from ‘copy_to_user’,
inlined from ‘override_release.part.11’ at /home/jpoimboe/git/linux/kernel/sys.c:1136:9:
/home/jpoimboe/git/linux/arch/x86/include/asm/uaccess.h:723:46: warning: call to ‘__copy_to_user_overflow’ declared with attribute warning: copy_to_user() buffer size is not provably correct
#define __copy_to_user_overflow(size, count) __copy_to_user_overflow()
^~~~~~~~~~~~~~~~~~~~~~~~~
/home/jpoimboe/git/linux/arch/x86/include/asm/uaccess.h:791:3: note: in expansion of macro ‘__copy_to_user_overflow’
__copy_to_user_overflow(sz, n);
^~~~~~~~~~~~~~~~~~~~~~~
This is from override_release()'s use of copy_to_user(). The object
code shows that __builtin_object_size() correctly reports 65 bytes for
the 'buf' object size. But the copy size ('copy + 1') isn't known at
compile-time. Thus the (bogus) warning.
Maybe I'm missing something but I don't even see a gcc bug. To me it
looks like a mismatch in expectations between the code and the compiler.
--
Josh
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[PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-18 15:10 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Kees Cook <keescook@chromium.org> - 2016-08-19 20:30 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-20 00:00 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-22 22:40 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-23 01:40 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Kees Cook <keescook@chromium.org> - 2016-08-23 03:00 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-23 06:30 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-23 00:20 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Kees Cook <keescook@chromium.org> - 2016-08-23 03:30 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-23 18:40 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-24 01:20 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-23 18:10 +0200
[PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-23 21:30 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Kees Cook <keescook@chromium.org> - 2016-08-24 05:50 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-25 23:00 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Kees Cook <keescook@chromium.org> - 2016-08-26 04:30 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-26 06:00 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Kees Cook <keescook@chromium.org> - 2016-08-26 15:50 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-26 16:00 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-26 23:10 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-26 23:10 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-27 02:40 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-29 16:50 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-29 17:40 +0200
[PATCH v2] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-29 19:10 +0200
Re: [PATCH v2] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-29 20:10 +0200
[PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-30 15:10 +0200
Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-30 19:10 +0200
Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Kees Cook <keescook@chromium.org> - 2016-08-30 20:20 +0200
Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-30 21:10 +0200
Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Kees Cook <keescook@chromium.org> - 2016-08-30 21:30 +0200
Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Al Viro <viro@ZenIV.linux.org.uk> - 2016-08-30 22:20 +0200
Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Kees Cook <keescook@chromium.org> - 2016-08-31 00:30 +0200
Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Mark Rutland <mark.rutland@arm.com> - 2016-08-31 11:50 +0200
Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-30 20:20 +0200
Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Al Viro <viro@ZenIV.linux.org.uk> - 2016-08-30 20:20 +0200
Re: [PATCH 2/2] mm/usercopy: enable usercopy size checking for modern versions of gcc Kees Cook <keescook@chromium.org> - 2016-08-30 20:40 +0200
[PATCH 1/2] mm/usercopy: get rid of "provably correct" warnings Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-23 21:30 +0200
Re: [PATCH 1/2] mm/usercopy: get rid of "provably correct" warnings Kees Cook <keescook@chromium.org> - 2016-08-24 04:40 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Andy Lutomirski <luto@kernel.org> - 2016-08-23 22:50 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-23 23:10 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-23 23:20 +0200
Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder Kees Cook <keescook@chromium.org> - 2016-08-24 03:50 +0200
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