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[PATCH v4 0/2] provide check for ro_after_init memory sections

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  [PATCH v4 0/2] provide check for ro_after_init memory sections Eddie Kovsky <ewk@edkovsky.org> - 2017-03-26 23:20 +0200
    [PATCH v4 2/2] extable: verify address is read-only Eddie Kovsky <ewk@edkovsky.org> - 2017-03-26 23:20 +0200
      Re: [PATCH v4 2/2] extable: verify address is read-only kbuild test robot <lkp@intel.com> - 2017-03-27 10:50 +0200
        Re: [PATCH v4 2/2] extable: verify address is read-only Kees Cook <keescook@chromium.org> - 2017-03-27 21:00 +0200
          Re: [PATCH v4 2/2] extable: verify address is read-only Eddie Kovsky <ewk@edkovsky.org> - 2017-03-29 05:30 +0200
            Re: [PATCH v4 2/2] extable: verify address is read-only Jessica Yu <jeyu@redhat.com> - 2017-03-30 05:40 +0200
              Re: [PATCH v4 2/2] extable: verify address is read-only Kees Cook <keescook@chromium.org> - 2017-03-30 18:30 +0200
                Re: [PATCH v4 2/2] extable: verify address is read-only Eddie Kovsky <ewk@edkovsky.org> - 2017-03-31 05:10 +0200
              Re: [PATCH v4 2/2] extable: verify address is read-only Kees Cook <keescook@chromium.org> - 2017-04-04 00:20 +0200

#1609402 — [PATCH v4 0/2] provide check for ro_after_init memory sections

Provide a mechanism for other functions to verify that their arguments
are read-only.

This implements the first half of a suggestion made by Kees Cook for
the Kernel Self Protection Project:

    - provide mechanism to check for ro_after_init memory areas, and
      reject structures not marked ro_after_init in vmbus_register()

      http://www.openwall.com/lists/kernel-hardening/2017/02/04/1

The idea is to prevent structures (including modules) that are not
read-only from being passed to functions. It builds upon the functions
in kernel/extable.c that test if an address is in the text section.

I have dropped the third patch that uses these features to check the
arguments to vmbus_register() because the maintainers have not been
receptive to using it. My goal right now is to get the API right.

I have test compiled this series on next-20170324 for x86.

Eddie Kovsky (2):
  module: verify address is read-only
  extable: verify address is read-only

 include/linux/kernel.h |  2 ++
 include/linux/module.h | 12 ++++++++++++
 kernel/extable.c       | 29 +++++++++++++++++++++++++++
 kernel/module.c        | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 96 insertions(+)

-- 
2.12.1

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#1609404 — [PATCH v4 2/2] extable: verify address is read-only

Provide a mechanism to check if the address of a variable is
const or ro_after_init. It mimics the existing functions that test if an
address is inside the kernel's text section.

The idea is to prevent structures that are not read-only from being
passed to functions. Other functions inside the kernel could then use
this capability to verify that their arguments are read-only.

This implements the first half of a suggestion made by Kees Cook for
the Kernel Self Protection Project:

	- provide mechanism to check for ro_after_init memory areas, and
	reject structures not marked ro_after_init in vmbus_register()

Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Eddie Kovsky <ewk@edkovsky.org>
---
Changes in v4:
 - Rename function core_kernel_ro_data() to core_kernel_rodata().
Changes in v3:
 - Fix missing declaration of is_module_rodata_address()
---
 include/linux/kernel.h |  2 ++
 kernel/extable.c       | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 4c26dc3a8295..5748784ca209 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -444,6 +444,8 @@ extern int core_kernel_data(unsigned long addr);
 extern int __kernel_text_address(unsigned long addr);
 extern int kernel_text_address(unsigned long addr);
 extern int func_ptr_is_kernel_text(void *ptr);
+extern int core_kernel_rodata(unsigned long addr);
+extern int kernel_ro_address(unsigned long addr);
 
 unsigned long int_sqrt(unsigned long);
 
diff --git a/kernel/extable.c b/kernel/extable.c
index 2676d7f8baf6..22562cfc6ac3 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -154,3 +154,32 @@ int func_ptr_is_kernel_text(void *ptr)
 		return 1;
 	return is_module_text_address(addr);
 }
+
+/**
+ * core_kernel_rodata - Verify address points to read-only section
+ * @addr: address to test
+ *
+ */
+int core_kernel_rodata(unsigned long addr)
+{
+	if (addr >= (unsigned long)__start_rodata &&
+	    addr < (unsigned long)__end_rodata)
+		return 1;
+
+	if (addr >= (unsigned long)__start_data_ro_after_init &&
+	    addr < (unsigned long)__end_data_ro_after_init)
+		return 1;
+
+	return 0;
+}
+
+/* Verify that address is const or ro_after_init. */
+int kernel_ro_address(unsigned long addr)
+{
+	if (core_kernel_rodata(addr))
+		return 1;
+	if (is_module_rodata_address(addr))
+		return 1;
+
+	return 0;
+}
-- 
2.12.1

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#1609580 — Re: [PATCH v4 2/2] extable: verify address is read-only

[Multipart message — attachments visible in raw view] — view raw

Hi Eddie,

[auto build test ERROR on next-20170323]
[cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc4]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Eddie-Kovsky/module-verify-address-is-read-only/20170327-142922
config: blackfin-BF561-EZKIT-SMP_defconfig (attached as .config)
compiler: bfin-uclinux-gcc (GCC) 6.2.0
reproduce:
        wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=blackfin 

All errors (new ones prefixed by >>):

   kernel/built-in.o: In function `core_kernel_rodata':
>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'

vim +169 kernel/extable.c

   163	int core_kernel_rodata(unsigned long addr)
   164	{
   165		if (addr >= (unsigned long)__start_rodata &&
   166		    addr < (unsigned long)__end_rodata)
   167			return 1;
   168	
 > 169		if (addr >= (unsigned long)__start_data_ro_after_init &&
   170		    addr < (unsigned long)__end_data_ro_after_init)
   171			return 1;
   172	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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#1610075 — Re: [PATCH v4 2/2] extable: verify address is read-only

On Mon, Mar 27, 2017 at 1:43 AM, kbuild test robot <lkp@intel.com> wrote:
> Hi Eddie,
>
> [auto build test ERROR on next-20170323]
> [cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc4]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>
> url:    https://github.com/0day-ci/linux/commits/Eddie-Kovsky/module-verify-address-is-read-only/20170327-142922
> config: blackfin-BF561-EZKIT-SMP_defconfig (attached as .config)
> compiler: bfin-uclinux-gcc (GCC) 6.2.0
> reproduce:
>         wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=blackfin
>
> All errors (new ones prefixed by >>):
>
>    kernel/built-in.o: In function `core_kernel_rodata':
>>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'

Hm, I'm confused about this. blackfin includes
include/asm-generic-vmlinux.lds.h and uses the RO_DATA macro (which
resolves to RO_DATA_SECTION to RO_AFTER_INIT_DATA which defines
__[start|end]_data_ro_after_init.

Also, it seems that commit d7c19b066dcf4bd19c4385e8065558d4e74f9e73
("mm: kmemleak: scan .data.ro_after_init") added a potentially
redundant section name (s390 already calls this
__[start|end]_ro_after_init). I'd like to get this cleaned up, since
having multiple names for the same thing is confusing:

diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S
index 000e6e91f6a0..3667d20e997f 100644
--- a/arch/s390/kernel/vmlinux.lds.S
+++ b/arch/s390/kernel/vmlinux.lds.S
@@ -62,9 +62,11 @@ SECTIONS

        . = ALIGN(PAGE_SIZE);
        __start_ro_after_init = .;
+       __start_data_ro_after_init = .;
        .data..ro_after_init : {
                 *(.data..ro_after_init)
        }
+       __end_data_ro_after_init = .;
        EXCEPTION_TABLE(16)
        . = ALIGN(PAGE_SIZE);
        __end_ro_after_init = .;

And it seems that this hunk is wrong (__end_ro_after_init includes
s390's exception table, etc). I think we should remove the
..._data_... name and use s390's name.

I'll send an adjustment patch, but we'll still need to deal with blackfin.

-Kees

>
> vim +169 kernel/extable.c
>
>    163  int core_kernel_rodata(unsigned long addr)
>    164  {
>    165          if (addr >= (unsigned long)__start_rodata &&
>    166              addr < (unsigned long)__end_rodata)
>    167                  return 1;
>    168
>  > 169          if (addr >= (unsigned long)__start_data_ro_after_init &&
>    170              addr < (unsigned long)__end_data_ro_after_init)
>    171                  return 1;
>    172
>
> ---
> 0-DAY kernel test infrastructure                Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation



-- 
Kees Cook
Pixel Security

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#1611536 — Re: [PATCH v4 2/2] extable: verify address is read-only

On 03/27/17, Kees Cook wrote:
> On Mon, Mar 27, 2017 at 1:43 AM, kbuild test robot <lkp@intel.com> wrote:
> > Hi Eddie,
> >
> > [auto build test ERROR on next-20170323]
> > [cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc4]
> > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> >
> > url:    https://github.com/0day-ci/linux/commits/Eddie-Kovsky/module-verify-address-is-read-only/20170327-142922
> > config: blackfin-BF561-EZKIT-SMP_defconfig (attached as .config)
> > compiler: bfin-uclinux-gcc (GCC) 6.2.0
> > reproduce:
> >         wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         # save the attached .config to linux build tree
> >         make.cross ARCH=blackfin
> >
> > All errors (new ones prefixed by >>):
> >
> >    kernel/built-in.o: In function `core_kernel_rodata':
> >>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
> >>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
> >>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
> >>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
> >>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
> >>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
> >>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
> >>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
> 
> Hm, I'm confused about this. blackfin includes
> include/asm-generic-vmlinux.lds.h and uses the RO_DATA macro (which
> resolves to RO_DATA_SECTION to RO_AFTER_INIT_DATA which defines
> __[start|end]_data_ro_after_init.
> 
> Also, it seems that commit d7c19b066dcf4bd19c4385e8065558d4e74f9e73
> ("mm: kmemleak: scan .data.ro_after_init") added a potentially
> redundant section name (s390 already calls this
> __[start|end]_ro_after_init). I'd like to get this cleaned up, since
> having multiple names for the same thing is confusing:
> 
> diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S
> index 000e6e91f6a0..3667d20e997f 100644
> --- a/arch/s390/kernel/vmlinux.lds.S
> +++ b/arch/s390/kernel/vmlinux.lds.S
> @@ -62,9 +62,11 @@ SECTIONS
> 
>         . = ALIGN(PAGE_SIZE);
>         __start_ro_after_init = .;
> +       __start_data_ro_after_init = .;
>         .data..ro_after_init : {
>                  *(.data..ro_after_init)
>         }
> +       __end_data_ro_after_init = .;
>         EXCEPTION_TABLE(16)
>         . = ALIGN(PAGE_SIZE);
>         __end_ro_after_init = .;
> 
> And it seems that this hunk is wrong (__end_ro_after_init includes
> s390's exception table, etc). I think we should remove the
> ..._data_... name and use s390's name.
> 
> I'll send an adjustment patch, but we'll still need to deal with blackfin.
> 
> -Kees
> 

Kees

I applied your patch (mm: fix section name for .data..ro_after_init) and
changed the new function in extable.c to use __[start|end]_ro_after_init
instead. The new version still builds without errors on x86, which isn't
surprising.

I've cross compiled this for blackfin and I'm able to reproduce the
build error. I'm still not sure why. As you pointed out, blackfin does
appear to use 'include/asm-generic/vmlinux.lds.h'. 

Eddie

> >
> > vim +169 kernel/extable.c
> >
> >    163  int core_kernel_rodata(unsigned long addr)
> >    164  {
> >    165          if (addr >= (unsigned long)__start_rodata &&
> >    166              addr < (unsigned long)__end_rodata)
> >    167                  return 1;
> >    168
> >  > 169          if (addr >= (unsigned long)__start_data_ro_after_init &&
> >    170              addr < (unsigned long)__end_data_ro_after_init)
> >    171                  return 1;
> >    172
> >
> > ---
> > 0-DAY kernel test infrastructure                Open Source Technology Center
> > https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
> 
> 
> 
> -- 
> Kees Cook
> Pixel Security

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#1612533 — Re: [PATCH v4 2/2] extable: verify address is read-only

+++ Eddie Kovsky [28/03/17 21:28 -0600]:
>On 03/27/17, Kees Cook wrote:
>> On Mon, Mar 27, 2017 at 1:43 AM, kbuild test robot <lkp@intel.com> wrote:
>> > Hi Eddie,
>> >
>> > [auto build test ERROR on next-20170323]
>> > [cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8 v4.9-rc7 v4.9-rc6 v4.11-rc4]
>> > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>> >
>> > url:    https://github.com/0day-ci/linux/commits/Eddie-Kovsky/module-verify-address-is-read-only/20170327-142922
>> > config: blackfin-BF561-EZKIT-SMP_defconfig (attached as .config)
>> > compiler: bfin-uclinux-gcc (GCC) 6.2.0
>> > reproduce:
>> >         wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>> >         chmod +x ~/bin/make.cross
>> >         # save the attached .config to linux build tree
>> >         make.cross ARCH=blackfin
>> >
>> > All errors (new ones prefixed by >>):
>> >
>> >    kernel/built-in.o: In function `core_kernel_rodata':
>> >>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> >>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> >>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>> >>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>> >>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> >>> kernel/extable.c:169: undefined reference to `__start_data_ro_after_init'
>> >>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>> >>> kernel/extable.c:169: undefined reference to `__end_data_ro_after_init'
>>
>> Hm, I'm confused about this. blackfin includes
>> include/asm-generic-vmlinux.lds.h and uses the RO_DATA macro (which
>> resolves to RO_DATA_SECTION to RO_AFTER_INIT_DATA which defines
>> __[start|end]_data_ro_after_init.
>>
>> Also, it seems that commit d7c19b066dcf4bd19c4385e8065558d4e74f9e73
>> ("mm: kmemleak: scan .data.ro_after_init") added a potentially
>> redundant section name (s390 already calls this
>> __[start|end]_ro_after_init). I'd like to get this cleaned up, since
>> having multiple names for the same thing is confusing:
>>
>> diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S
>> index 000e6e91f6a0..3667d20e997f 100644
>> --- a/arch/s390/kernel/vmlinux.lds.S
>> +++ b/arch/s390/kernel/vmlinux.lds.S
>> @@ -62,9 +62,11 @@ SECTIONS
>>
>>         . = ALIGN(PAGE_SIZE);
>>         __start_ro_after_init = .;
>> +       __start_data_ro_after_init = .;
>>         .data..ro_after_init : {
>>                  *(.data..ro_after_init)
>>         }
>> +       __end_data_ro_after_init = .;
>>         EXCEPTION_TABLE(16)
>>         . = ALIGN(PAGE_SIZE);
>>         __end_ro_after_init = .;
>>
>> And it seems that this hunk is wrong (__end_ro_after_init includes
>> s390's exception table, etc). I think we should remove the
>> ..._data_... name and use s390's name.
>>
>> I'll send an adjustment patch, but we'll still need to deal with blackfin.
>>
>> -Kees
>>
>
>Kees
>
>I applied your patch (mm: fix section name for .data..ro_after_init) and
>changed the new function in extable.c to use __[start|end]_ro_after_init
>instead. The new version still builds without errors on x86, which isn't
>surprising.
>
>I've cross compiled this for blackfin and I'm able to reproduce the
>build error. I'm still not sure why. As you pointed out, blackfin does
>appear to use 'include/asm-generic/vmlinux.lds.h'.

This appears to be because blackfin is one of the 2 arches that
prepends an underscore '_' to all symbols defined in C. I noticed that
__{start,end}_data_ro_after_init in vmlinux.lds.h are not wrapped with
VMLINUX_SYMBOL() which adds the necessary prefix for arches that have
HAVE_UNDERSCORE_SYMBOL_PREFIX, hence the undefined reference.

The below patch fixed the build error for me, if it works for you then
I can send a formal patch.

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 4e09b28..7b262f7 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -260,9 +260,9 @@
  */
 #ifndef RO_AFTER_INIT_DATA
 #define RO_AFTER_INIT_DATA						\
-	__start_data_ro_after_init = .;					\
+	VMLINUX_SYMBOL(__start_data_ro_after_init) = .;			\
 	*(.data..ro_after_init)						\
-	__end_data_ro_after_init = .;
+	VMLINUX_SYMBOL(__end_data_ro_after_init) = .;
 #endif
 
 /*

Jessica

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#1613272 — Re: [PATCH v4 2/2] extable: verify address is read-only

On Wed, Mar 29, 2017 at 8:27 PM, Jessica Yu <jeyu@redhat.com> wrote:
> +++ Eddie Kovsky [28/03/17 21:28 -0600]:
>
>> On 03/27/17, Kees Cook wrote:
>>>
>>> On Mon, Mar 27, 2017 at 1:43 AM, kbuild test robot <lkp@intel.com> wrote:
>>> > Hi Eddie,
>>> >
>>> > [auto build test ERROR on next-20170323]
>>> > [cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8
>>> > v4.9-rc7 v4.9-rc6 v4.11-rc4]
>>> > [if your patch is applied to the wrong git tree, please drop us a note
>>> > to help improve the system]
>>> >
>>> > url:
>>> > https://github.com/0day-ci/linux/commits/Eddie-Kovsky/module-verify-address-is-read-only/20170327-142922
>>> > config: blackfin-BF561-EZKIT-SMP_defconfig (attached as .config)
>>> > compiler: bfin-uclinux-gcc (GCC) 6.2.0
>>> > reproduce:
>>> >         wget
>>> > https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O
>>> > ~/bin/make.cross
>>> >         chmod +x ~/bin/make.cross
>>> >         # save the attached .config to linux build tree
>>> >         make.cross ARCH=blackfin
>>> >
>>> > All errors (new ones prefixed by >>):
>>> >
>>> >    kernel/built-in.o: In function `core_kernel_rodata':
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__start_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__start_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__end_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__end_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__start_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__start_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__end_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__end_data_ro_after_init'
>>>
>>> Hm, I'm confused about this. blackfin includes
>>> include/asm-generic-vmlinux.lds.h and uses the RO_DATA macro (which
>>> resolves to RO_DATA_SECTION to RO_AFTER_INIT_DATA which defines
>>> __[start|end]_data_ro_after_init.
>>>
>>> Also, it seems that commit d7c19b066dcf4bd19c4385e8065558d4e74f9e73
>>> ("mm: kmemleak: scan .data.ro_after_init") added a potentially
>>> redundant section name (s390 already calls this
>>> __[start|end]_ro_after_init). I'd like to get this cleaned up, since
>>> having multiple names for the same thing is confusing:
>>>
>>> diff --git a/arch/s390/kernel/vmlinux.lds.S
>>> b/arch/s390/kernel/vmlinux.lds.S
>>> index 000e6e91f6a0..3667d20e997f 100644
>>> --- a/arch/s390/kernel/vmlinux.lds.S
>>> +++ b/arch/s390/kernel/vmlinux.lds.S
>>> @@ -62,9 +62,11 @@ SECTIONS
>>>
>>>         . = ALIGN(PAGE_SIZE);
>>>         __start_ro_after_init = .;
>>> +       __start_data_ro_after_init = .;
>>>         .data..ro_after_init : {
>>>                  *(.data..ro_after_init)
>>>         }
>>> +       __end_data_ro_after_init = .;
>>>         EXCEPTION_TABLE(16)
>>>         . = ALIGN(PAGE_SIZE);
>>>         __end_ro_after_init = .;
>>>
>>> And it seems that this hunk is wrong (__end_ro_after_init includes
>>> s390's exception table, etc). I think we should remove the
>>> ..._data_... name and use s390's name.
>>>
>>> I'll send an adjustment patch, but we'll still need to deal with
>>> blackfin.
>>>
>>> -Kees
>>>
>>
>> Kees
>>
>> I applied your patch (mm: fix section name for .data..ro_after_init) and
>> changed the new function in extable.c to use __[start|end]_ro_after_init
>> instead. The new version still builds without errors on x86, which isn't
>> surprising.
>>
>> I've cross compiled this for blackfin and I'm able to reproduce the
>> build error. I'm still not sure why. As you pointed out, blackfin does
>> appear to use 'include/asm-generic/vmlinux.lds.h'.
>
>
> This appears to be because blackfin is one of the 2 arches that
> prepends an underscore '_' to all symbols defined in C. I noticed that
> __{start,end}_data_ro_after_init in vmlinux.lds.h are not wrapped with
> VMLINUX_SYMBOL() which adds the necessary prefix for arches that have
> HAVE_UNDERSCORE_SYMBOL_PREFIX, hence the undefined reference.

Argh. Thank you for catching this! Yeah, that would have taken me
forever to find.

> The below patch fixed the build error for me, if it works for you then
> I can send a formal patch.
>
> diff --git a/include/asm-generic/vmlinux.lds.h
> b/include/asm-generic/vmlinux.lds.h
> index 4e09b28..7b262f7 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -260,9 +260,9 @@
>  */
> #ifndef RO_AFTER_INIT_DATA
> #define RO_AFTER_INIT_DATA                                              \
> -       __start_data_ro_after_init = .;                                 \
> +       VMLINUX_SYMBOL(__start_data_ro_after_init) = .;                 \
>         *(.data..ro_after_init)                                         \
> -       __end_data_ro_after_init = .;
> +       VMLINUX_SYMBOL(__end_data_ro_after_init) = .;
> #endif

I don't have a blackfin cross-compiler set up, but I'm sure that'll
fix it. If you can, please base it on -next, since I rename
__[start|end]_data_ro_after_init to __[start|end]_ro_after_init (to
match the existing s390 symbols of the same purpose):

https://lkml.org/lkml/2017/3/27/685

akpm is carrying that patch, so this follow-up should likely go to him too.

Thanks!

-Kees

-- 
Kees Cook
Pixel Security

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#1613588 — Re: [PATCH v4 2/2] extable: verify address is read-only

On 03/30/17, Kees Cook wrote:
> On Wed, Mar 29, 2017 at 8:27 PM, Jessica Yu <jeyu@redhat.com> wrote:
> > +++ Eddie Kovsky [28/03/17 21:28 -0600]:
> >
> >> On 03/27/17, Kees Cook wrote:
> >>>
> >>> On Mon, Mar 27, 2017 at 1:43 AM, kbuild test robot <lkp@intel.com> wrote:
> >>> > Hi Eddie,
> >>> >
> >>> > [auto build test ERROR on next-20170323]
> >>> > [cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8
> >>> > v4.9-rc7 v4.9-rc6 v4.11-rc4]
> >>> > [if your patch is applied to the wrong git tree, please drop us a note
> >>> > to help improve the system]
> >>> >
> >>> > url:
> >>> > https://github.com/0day-ci/linux/commits/Eddie-Kovsky/module-verify-address-is-read-only/20170327-142922
> >>> > config: blackfin-BF561-EZKIT-SMP_defconfig (attached as .config)
> >>> > compiler: bfin-uclinux-gcc (GCC) 6.2.0
> >>> > reproduce:
> >>> >         wget
> >>> > https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O
> >>> > ~/bin/make.cross
> >>> >         chmod +x ~/bin/make.cross
> >>> >         # save the attached .config to linux build tree
> >>> >         make.cross ARCH=blackfin
> >>> >
> >>> > All errors (new ones prefixed by >>):
> >>> >
> >>> >    kernel/built-in.o: In function `core_kernel_rodata':
> >>> >>> kernel/extable.c:169: undefined reference to
> >>> >>> `__start_data_ro_after_init'
> >>> >>> kernel/extable.c:169: undefined reference to
> >>> >>> `__start_data_ro_after_init'
> >>> >>> kernel/extable.c:169: undefined reference to
> >>> >>> `__end_data_ro_after_init'
> >>> >>> kernel/extable.c:169: undefined reference to
> >>> >>> `__end_data_ro_after_init'
> >>> >>> kernel/extable.c:169: undefined reference to
> >>> >>> `__start_data_ro_after_init'
> >>> >>> kernel/extable.c:169: undefined reference to
> >>> >>> `__start_data_ro_after_init'
> >>> >>> kernel/extable.c:169: undefined reference to
> >>> >>> `__end_data_ro_after_init'
> >>> >>> kernel/extable.c:169: undefined reference to
> >>> >>> `__end_data_ro_after_init'
> >>>
> >>> Hm, I'm confused about this. blackfin includes
> >>> include/asm-generic-vmlinux.lds.h and uses the RO_DATA macro (which
> >>> resolves to RO_DATA_SECTION to RO_AFTER_INIT_DATA which defines
> >>> __[start|end]_data_ro_after_init.
> >>>
> >>> Also, it seems that commit d7c19b066dcf4bd19c4385e8065558d4e74f9e73
> >>> ("mm: kmemleak: scan .data.ro_after_init") added a potentially
> >>> redundant section name (s390 already calls this
> >>> __[start|end]_ro_after_init). I'd like to get this cleaned up, since
> >>> having multiple names for the same thing is confusing:
> >>>
> >>> diff --git a/arch/s390/kernel/vmlinux.lds.S
> >>> b/arch/s390/kernel/vmlinux.lds.S
> >>> index 000e6e91f6a0..3667d20e997f 100644
> >>> --- a/arch/s390/kernel/vmlinux.lds.S
> >>> +++ b/arch/s390/kernel/vmlinux.lds.S
> >>> @@ -62,9 +62,11 @@ SECTIONS
> >>>
> >>>         . = ALIGN(PAGE_SIZE);
> >>>         __start_ro_after_init = .;
> >>> +       __start_data_ro_after_init = .;
> >>>         .data..ro_after_init : {
> >>>                  *(.data..ro_after_init)
> >>>         }
> >>> +       __end_data_ro_after_init = .;
> >>>         EXCEPTION_TABLE(16)
> >>>         . = ALIGN(PAGE_SIZE);
> >>>         __end_ro_after_init = .;
> >>>
> >>> And it seems that this hunk is wrong (__end_ro_after_init includes
> >>> s390's exception table, etc). I think we should remove the
> >>> ..._data_... name and use s390's name.
> >>>
> >>> I'll send an adjustment patch, but we'll still need to deal with
> >>> blackfin.
> >>>
> >>> -Kees
> >>>
> >>
> >> Kees
> >>
> >> I applied your patch (mm: fix section name for .data..ro_after_init) and
> >> changed the new function in extable.c to use __[start|end]_ro_after_init
> >> instead. The new version still builds without errors on x86, which isn't
> >> surprising.
> >>
> >> I've cross compiled this for blackfin and I'm able to reproduce the
> >> build error. I'm still not sure why. As you pointed out, blackfin does
> >> appear to use 'include/asm-generic/vmlinux.lds.h'.
> >
> >
> > This appears to be because blackfin is one of the 2 arches that
> > prepends an underscore '_' to all symbols defined in C. I noticed that
> > __{start,end}_data_ro_after_init in vmlinux.lds.h are not wrapped with
> > VMLINUX_SYMBOL() which adds the necessary prefix for arches that have
> > HAVE_UNDERSCORE_SYMBOL_PREFIX, hence the undefined reference.
> 
> Argh. Thank you for catching this! Yeah, that would have taken me
> forever to find.
> 
> > The below patch fixed the build error for me, if it works for you then
> > I can send a formal patch.
> >
> > diff --git a/include/asm-generic/vmlinux.lds.h
> > b/include/asm-generic/vmlinux.lds.h
> > index 4e09b28..7b262f7 100644
> > --- a/include/asm-generic/vmlinux.lds.h
> > +++ b/include/asm-generic/vmlinux.lds.h
> > @@ -260,9 +260,9 @@
> >  */
> > #ifndef RO_AFTER_INIT_DATA
> > #define RO_AFTER_INIT_DATA                                              \
> > -       __start_data_ro_after_init = .;                                 \
> > +       VMLINUX_SYMBOL(__start_data_ro_after_init) = .;                 \
> >         *(.data..ro_after_init)                                         \
> > -       __end_data_ro_after_init = .;
> > +       VMLINUX_SYMBOL(__end_data_ro_after_init) = .;
> > #endif
> 
> I don't have a blackfin cross-compiler set up, but I'm sure that'll
> fix it. If you can, please base it on -next, since I rename
> __[start|end]_data_ro_after_init to __[start|end]_ro_after_init (to
> match the existing s390 symbols of the same purpose):
> 
> https://lkml.org/lkml/2017/3/27/685
> 
I applied Jessica's patch and tested this again with a blackfin cross-compiler.
It fixes the error building extable.c.


> akpm is carrying that patch, so this follow-up should likely go to him too.
> 
> Thanks!
> 
> -Kees
> 
> -- 
> Kees Cook
> Pixel Security

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#1615592 — Re: [PATCH v4 2/2] extable: verify address is read-only

On Wed, Mar 29, 2017 at 8:27 PM, Jessica Yu <jeyu@redhat.com> wrote:
> +++ Eddie Kovsky [28/03/17 21:28 -0600]:
>
>> On 03/27/17, Kees Cook wrote:
>>>
>>> On Mon, Mar 27, 2017 at 1:43 AM, kbuild test robot <lkp@intel.com> wrote:
>>> > Hi Eddie,
>>> >
>>> > [auto build test ERROR on next-20170323]
>>> > [cannot apply to linus/master linux/master jeyu/modules-next v4.9-rc8
>>> > v4.9-rc7 v4.9-rc6 v4.11-rc4]
>>> > [if your patch is applied to the wrong git tree, please drop us a note
>>> > to help improve the system]
>>> >
>>> > url:
>>> > https://github.com/0day-ci/linux/commits/Eddie-Kovsky/module-verify-address-is-read-only/20170327-142922
>>> > config: blackfin-BF561-EZKIT-SMP_defconfig (attached as .config)
>>> > compiler: bfin-uclinux-gcc (GCC) 6.2.0
>>> > reproduce:
>>> >         wget
>>> > https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O
>>> > ~/bin/make.cross
>>> >         chmod +x ~/bin/make.cross
>>> >         # save the attached .config to linux build tree
>>> >         make.cross ARCH=blackfin
>>> >
>>> > All errors (new ones prefixed by >>):
>>> >
>>> >    kernel/built-in.o: In function `core_kernel_rodata':
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__start_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__start_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__end_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__end_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__start_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__start_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__end_data_ro_after_init'
>>> >>> kernel/extable.c:169: undefined reference to
>>> >>> `__end_data_ro_after_init'
>>>
>>> Hm, I'm confused about this. blackfin includes
>>> include/asm-generic-vmlinux.lds.h and uses the RO_DATA macro (which
>>> resolves to RO_DATA_SECTION to RO_AFTER_INIT_DATA which defines
>>> __[start|end]_data_ro_after_init.
>>>
>>> Also, it seems that commit d7c19b066dcf4bd19c4385e8065558d4e74f9e73
>>> ("mm: kmemleak: scan .data.ro_after_init") added a potentially
>>> redundant section name (s390 already calls this
>>> __[start|end]_ro_after_init). I'd like to get this cleaned up, since
>>> having multiple names for the same thing is confusing:
>>>
>>> diff --git a/arch/s390/kernel/vmlinux.lds.S
>>> b/arch/s390/kernel/vmlinux.lds.S
>>> index 000e6e91f6a0..3667d20e997f 100644
>>> --- a/arch/s390/kernel/vmlinux.lds.S
>>> +++ b/arch/s390/kernel/vmlinux.lds.S
>>> @@ -62,9 +62,11 @@ SECTIONS
>>>
>>>         . = ALIGN(PAGE_SIZE);
>>>         __start_ro_after_init = .;
>>> +       __start_data_ro_after_init = .;
>>>         .data..ro_after_init : {
>>>                  *(.data..ro_after_init)
>>>         }
>>> +       __end_data_ro_after_init = .;
>>>         EXCEPTION_TABLE(16)
>>>         . = ALIGN(PAGE_SIZE);
>>>         __end_ro_after_init = .;
>>>
>>> And it seems that this hunk is wrong (__end_ro_after_init includes
>>> s390's exception table, etc). I think we should remove the
>>> ..._data_... name and use s390's name.
>>>
>>> I'll send an adjustment patch, but we'll still need to deal with
>>> blackfin.
>>>
>>> -Kees
>>>
>>
>> Kees
>>
>> I applied your patch (mm: fix section name for .data..ro_after_init) and
>> changed the new function in extable.c to use __[start|end]_ro_after_init
>> instead. The new version still builds without errors on x86, which isn't
>> surprising.
>>
>> I've cross compiled this for blackfin and I'm able to reproduce the
>> build error. I'm still not sure why. As you pointed out, blackfin does
>> appear to use 'include/asm-generic/vmlinux.lds.h'.
>
>
> This appears to be because blackfin is one of the 2 arches that
> prepends an underscore '_' to all symbols defined in C. I noticed that
> __{start,end}_data_ro_after_init in vmlinux.lds.h are not wrapped with
> VMLINUX_SYMBOL() which adds the necessary prefix for arches that have
> HAVE_UNDERSCORE_SYMBOL_PREFIX, hence the undefined reference.
>
> The below patch fixed the build error for me, if it works for you then
> I can send a formal patch.
>
> diff --git a/include/asm-generic/vmlinux.lds.h
> b/include/asm-generic/vmlinux.lds.h
> index 4e09b28..7b262f7 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -260,9 +260,9 @@
>  */
> #ifndef RO_AFTER_INIT_DATA
> #define RO_AFTER_INIT_DATA                                              \
> -       __start_data_ro_after_init = .;                                 \
> +       VMLINUX_SYMBOL(__start_data_ro_after_init) = .;                 \
>         *(.data..ro_after_init)                                         \
> -       __end_data_ro_after_init = .;
> +       VMLINUX_SYMBOL(__end_data_ro_after_init) = .;
> #endif
>
> /*
>
> Jessica

Do you have a moment to send this? I'd like to get it in for v4.11 (my
renaming has landed, so you'll have to rebase). If not, I can do it.
:)

-Kees

-- 
Kees Cook
Pixel Security

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