linux-hardening - Re: [linux-next:master 2819/11071] fs/ceph/addr.c:794:12: warning: stack frame size (2096) exceeds limit (2048) in 'ceph_writepages

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Date:   Wed, 21 Jun 2023 14:44:44 -0700
From:   Kees Cook <keescook@...omium.org>
To:     kernel test robot <lkp@...el.com>
Cc:     llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
        Linux Memory Management List <linux-mm@...ck.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [linux-next:master 2819/11071] fs/ceph/addr.c:794:12: warning:
 stack frame size (2096) exceeds limit (2048) in 'ceph_writepages_start'

On Wed, Jun 21, 2023 at 02:39:39PM -0700, Kees Cook wrote:
> On Wed, Jun 21, 2023 at 06:56:36AM +0800, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> > head:   9dbf40840551df336c95ce2a3adbdd25ed53c0ef
> > commit: df8fc4e934c12b906d08050d7779f292b9c5c6b5 [2819/11071] kbuild: Enable -fstrict-flex-arrays=3
> 
> This looks very much like:
> https://lore.kernel.org/all/202306100035.VTusNhm4-lkp@intel.com/
> 
> > config: riscv-randconfig-r004-20230620 (https://download.01.org/0day-ci/archive/20230621/202306210637.TpfYq9gM-lkp@intel.com/config)
> > compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
> > reproduce: (https://download.01.org/0day-ci/archive/20230621/202306210637.TpfYq9gM-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@...el.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202306210637.TpfYq9gM-lkp@intel.com/
> > 
> > All warnings (new ones prefixed by >>):
> > 
> > >> fs/ceph/addr.c:794:12: warning: stack frame size (2096) exceeds limit (2048) in 'ceph_writepages_start' [-Wframe-larger-than]
> >    static int ceph_writepages_start(struct address_space *mapping,
> >               ^
> >    1820/2096 (86.83%) spills, 276/2096 (13.17%) variables
> >    1 warning generated.
> 
> This appears to be a clang stack slot reuse issue. It continues to be
> investigated.

We're currently tracking it here, though we may need to split the bug
up:
https://github.com/ClangBuiltLinux/linux/issues/39

-- 
Kees Cook