Re: [PATCH v2 6/7] percpu: Add __alloc_size attributes for better bounds checking

Kees Cook
2021-08-20T05:27:30Z

On Thu, Aug 19, 2021 at 10:11:15PM -0700, Andrew Morton wrote:
> On Wed, 18 Aug 2021 14:40:20 -0700 Kees Cook <keescook@chromium.org> wrote:
>
> > As already done in GrapheneOS, add the __alloc_size attribute for
> > appropriate percpu allocator interfaces, to provide additional hinting
> > for better bounds checking, assisting CONFIG_FORTIFY_SOURCE and other
> > compiler optimizations.
> >
>
> Caught one, I assume:
>
> In file included from ./include/linux/string.h:262,
> from ./include/linux/bitmap.h:11,
> from ./include/linux/cpumask.h:12,
> from ./arch/x86/include/asm/cpumask.h:5,
> from ./arch/x86/include/asm/msr.h:11,
> from ./arch/x86/include/asm/processor.h:22,
> from ./arch/x86/include/asm/cpufeature.h:5,
> from ./arch/x86/include/asm/thread_info.h:53,
> from ./include/linux/thread_info.h:60,
> from ./arch/x86/include/asm/preempt.h:7,
> from ./include/linux/preempt.h:78,
> from ./include/linux/spinlock.h:55,
> from ./include/linux/mmzone.h:8,
> from ./include/linux/gfp.h:6,
> from ./include/linux/slab.h:15,
> from drivers/misc/lkdtm/heap.c:7:
> In function 'memset',
> inlined from 'lkdtm_VMALLOC_LINEAR_OVERFLOW' at drivers/misc/lkdtm/heap.c:27:2:
> ./include/linux/fortify-string.h:172:3: error: call to '__write_overflow' declared with attribute error: detected write beyond size of object passed as 1st parameter
> 172 | __write_overflow();
> | ^~~~~~~~~~~~~~~~~~
> make[3]: *** [drivers/misc/lkdtm/heap.o] Error 1
> make[2]: *** [drivers/misc/lkdtm] Error 2
> make[1]: *** [drivers/misc] Error 2
> make: *** [drivers] Error 2
>
> I want to get a kernel release out, so I'll hide
> mm-vmalloc-add-__alloc_size-attributes-for-better-bounds-checking.patch
> for now.

In the cover letter[1], I listed the needed fixes that were sent
separately from this series. Quoting here:

> To build without warnings, this series needs a couple small fixes for
> allmodconfig, which I sent separately:
> https://lore.kernel.org/lkml/20210818174855.2307828-5-keescook@chromium.org/
> https://lore.kernel.org/lkml/20210818044252.1533634-1-keescook@chromium.org/
> https://lore.kernel.org/lkml/20210818043912.1466447-1-keescook@chromium.org/

What you hit is the first one, which is already in Greg's tree:
https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git/commit/?h=char-misc-next&id=e6d468d32cd084edd030a8bae76440b17b854b5c

The other two have also been taken:
https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git/commit/?h=staging-next&id=cbe34165cc1b7d1110b268ba8b9f30843c941639
https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git/commit/?id=a31e5a4158d03595ca4258b94397d4097be0ebe4

-Kees

[1] https://lore.kernel.org/lkml/20210818214021.2476230-1-keescook@chromium.org/

--
Kees Cook