linux-kernel - Re: [kernel-hardening] [PATCH v3 2/3] x86/fpu: tighten validation of user-supplied xstate

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Message-ID: <1506025307.5486.24.camel@redhat.com>
Date:   Thu, 21 Sep 2017 16:21:47 -0400
From:   Rik van Riel <riel@...hat.com>
To:     Eric Biggers <ebiggers3@...il.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Ingo Molnar <mingo@...nel.org>, Kevin Hao <haokexin@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Michael Halcrow <mhalcrow@...gle.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [kernel-hardening] [PATCH v3 2/3] x86/fpu: tighten validation
 of user-supplied xstate_header

On Thu, 2017-09-21 at 11:52 -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> Move validation of user-supplied xstate_headers into a helper
> function
> and call it from both the ptrace and sigreturn syscall paths.  The
> new
> function also considers it to be an error if *any* reserved bits are
> set, whereas before we were just clearing most of them.
> 
> This should reduce the chance of bugs that fail to correctly validate
> user-supplied XSAVE areas.  It also will expose any broken userspace
> programs that set the other reserved bits; this is desirable because
> such programs will lose compatibility with future CPUs and kernels if
> those bits are ever used for anything.  (There shouldn't be any such
> programs, and in fact in the case where the compacted format is in
> use
> we were already validating xfeatures.  But you never know...)
> 
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Fenghua Yu <fenghua.yu@...el.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Kevin Hao <haokexin@...il.com>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Wanpeng Li <wanpeng.li@...mail.com>
> Cc: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> 
Reviewed-by: Rik van Riel <riel@...hat.com>

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