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

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

[kernel test robot]

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];
                                           ~~~~~~~~~~~~~~~~^~~~~


vim +181 kernel/kallsyms.c

^1da177e4c3f41 Linus Torvalds 2005-04-16  173  
30f3bb09778de6 Zhen Lei       2022-11-15  174  unsigned long kallsyms_sym_address(int idx)
2213e9a66bb87d Ard Biesheuvel 2016-03-15  175  {
2213e9a66bb87d Ard Biesheuvel 2016-03-15  176  	if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
2213e9a66bb87d Ard Biesheuvel 2016-03-15  177  		return kallsyms_addresses[idx];
2213e9a66bb87d Ard Biesheuvel 2016-03-15  178  
2213e9a66bb87d Ard Biesheuvel 2016-03-15  179  	/* values are unsigned offsets if --absolute-percpu is not in effect */
2213e9a66bb87d Ard Biesheuvel 2016-03-15  180  	if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
2213e9a66bb87d Ard Biesheuvel 2016-03-15 @181  		return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
2213e9a66bb87d Ard Biesheuvel 2016-03-15  182  
2213e9a66bb87d Ard Biesheuvel 2016-03-15  183  	/* ...otherwise, positive offsets are absolute values */
2213e9a66bb87d Ard Biesheuvel 2016-03-15  184  	if (kallsyms_offsets[idx] >= 0)
2213e9a66bb87d Ard Biesheuvel 2016-03-15  185  		return kallsyms_offsets[idx];
2213e9a66bb87d Ard Biesheuvel 2016-03-15  186  
2213e9a66bb87d Ard Biesheuvel 2016-03-15  187  	/* ...and negative offsets are relative to kallsyms_relative_base - 1 */
2213e9a66bb87d Ard Biesheuvel 2016-03-15  188  	return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
2213e9a66bb87d Ard Biesheuvel 2016-03-15  189  }
2213e9a66bb87d Ard Biesheuvel 2016-03-15  190  

:::::: The code at line 181 was first introduced by commit
:::::: 2213e9a66bb87d8344a1256b4ef568220d9587fb kallsyms: add support for relative offsets in kallsyms address table

:::::: TO: Ard Biesheuvel <ard.biesheuvel@linaro.org>
:::::: CC: Linus Torvalds <torvalds@linux-foundation.org>

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

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

[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.

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?

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

[Masahiro Yamada]

On Tue, Apr 23, 2024 at 3:57 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> 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.
>
> 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?


Then, I am fine with b (i.e. v4) for now.

Maybe, I may want to kill PROVIDE() when I have time.




-- 
Best Regards
Masahiro Yamada

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

[Alexander Stein]

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?
> 
> 


-- 
TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
Amtsgericht München, HRB 105018
Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
http://www.tq-group.com/