linux-kernel - Re: [PATCH 05/20] signal/mips: Update (_save|_restore)_fp

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Message-ID: <202110210906.AA70D50BA@keescook>
Date:   Thu, 21 Oct 2021 09:06:50 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Maciej Rozycki <macro@...am.me.uk>, linux-mips@...r.kernel.org
Subject: Re: [PATCH 05/20] signal/mips: Update (_save|_restore)_fp_context to
 fail with -EFAULT

On Wed, Oct 20, 2021 at 12:43:51PM -0500, Eric W. Biederman wrote:
> When an instruction to save or restore a register from the stack fails
> in _save_fp_context or _restore_fp_context return with -EFAULT.  This
> change was made to r2300_fpu.S[1] but it looks like it got lost with
> the introduction of EX2[2].  This is also what the other implementation
> of _save_fp_context and _restore_fp_context in r4k_fpu.S does, and
> what is needed for the callers to be able to handle the error.
> 
> Furthermore calling do_exit(SIGSEGV) from bad_stack is wrong because
> it does not terminate the entire process it just terminates a single
> thread.
> 
> As the changed code was the only caller of arch/mips/kernel/syscall.c:bad_stack
> remove the problematic and now unused helper function.
> 
> Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Cc: Maciej Rozycki <macro@...am.me.uk>
> Cc: linux-mips@...r.kernel.org
> [1] 35938a00ba86 ("MIPS: Fix ISA I FP sigcontext access violation handling")
> [2] f92722dc4545 ("MIPS: Correct MIPS I FP sigcontext layout")
> Fixes: f92722dc4545 ("MIPS: Correct MIPS I FP sigcontext layout")
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook