linux-kernel - Re: [PATCH 4/5] Makefile: Enable -Warray-bounds

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Date:   Wed, 2 Feb 2022 19:03:39 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kbuild@...r.kernel.org,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        clang-built-linux@...glegroups.com, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 4/5] Makefile: Enable -Warray-bounds

On Wed, Feb 02, 2022 at 03:33:11PM -0800, Guenter Roeck wrote:
> On 2/2/22 12:56, Kees Cook wrote:
> > On Wed, Feb 02, 2022 at 08:09:03AM -0800, Guenter Roeck wrote:
> > > xtensa:allmodconfig:
> > > --------------
> > > Error log:
> > > In file included from include/linux/uaccess.h:11,
> > >                   from include/linux/sched/task.h:11,
> > >                   from arch/xtensa/kernel/process.c:21:
> > > arch/xtensa/kernel/process.c: In function 'copy_thread':
> > > arch/xtensa/kernel/process.c:262:52: error: array subscript 53 is above array bounds of 'long unsigned int[16]'
> > 
> > I assume this is a weird cast. I will also check this one out.
> > 
> 
>                                 int callinc = (regs->areg[0] >> 30) & 3;
>                                 int caller_ars = XCHAL_NUM_AREGS - callinc * 4;
>                                 put_user(regs->areg[caller_ars+1],
>                                          ^^^^^^^^^^^^^^^^^^^^^^^^
>                                          (unsigned __user*)(usp - 12));
> 
> I think the problem is that XCHAL_NUM_AREGS can be up to 64,
> but the size of struct pt_regs->areg[] is fixed to 16.

Yeah, that's what I found too. The comment about pt_regs::areg seems to
hint that things treat pt_regs differently. I've asked on the xtensa list:
https://lore.kernel.org/linux-hardening/202202021501.DA6594BFC@keescook/

-- 
Kees Cook