Re: [masahiroy-kbuild:kbuild 5/7] kernel/kallsyms.c:181:56: warning: array subscript is outside array bounds

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Hi,

Am Dienstag, 23. April 2024, 08:57:16 CEST schrieb Ard Biesheuvel:
> On Tue, 23 Apr 2024 at 05:50, kernel test robot <lkp@intel.com> wrote:
> >
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git kbuild
> > head:   8246a1e9b922c0e797ec28d8a602de1384ff8140
> > commit: 0bdad28369fc5e93de39b5046228ed78e982fc71 [5/7] kallsyms: Avoid weak references for kallsyms symbols
> > config: i386-randconfig-001-20240423 (https://download.01.org/0day-ci/archive/20240423/202404231102.r0G0StUJ-lkp@intel.com/config)
> > compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240423/202404231102.r0G0StUJ-lkp@intel.com/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202404231102.r0G0StUJ-lkp@intel.com/
> >
> > Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
> >
> > All warnings (new ones prefixed by >>):
> >
> >    kernel/kallsyms.c: In function 'get_symbol_pos':
> > >> kernel/kallsyms.c:181:56: warning: array subscript is outside array bounds [-Warray-bounds]
> >       return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
> >
> 
> OK, so weak definitions result in compiler warnings. I don't know
> whether C requires weak definitions of array types are always the same
> size.

It's not just compiler warnings. UBSAN is also triggered by this commit.

> UBSAN: array-index-out-of-bounds in ../kernel/kallsyms.c:181:56
> index 64143 is out of range for type 'int [1]'
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.9.0-rc5-next-20240423+ #2422 cee92685fac34b7fb981de78571f7250231badab

[1] might also be affected by this as CONFIG_UBSAN_BOUNDS=y is set.

Best regards,
Alexander

[1] https://lore.kernel.org/linux-kbuild/691143b5-4636-4911-9c93-437b95f46157@amd.com/T/#m3e5e9112bac8a56b8a7dfa6a19cbc03dcb43a480

> We could work around this by
> a) emitting the weak definitions into a separate object file, although
> this may still violate C, and does not hide the issue from LTO
> b) go back to using PROVIDE() in the linker scripts
> 
> @Masahiro: any preference?
> 
> 


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