linux-kernel - Re: [PATCH v2 0/3] x86/fpu: prevent leaking FPU registers via invalid FPU state

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Date:   Tue, 19 Sep 2017 20:03:05 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Eric Biggers <ebiggers3@...il.com>, Ingo Molnar <mingo@...nel.org>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <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>,
        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: [PATCH v2 0/3] x86/fpu: prevent leaking FPU registers via invalid
 FPU state

On Tue, Sep 19, 2017 at 5:44 PM, Eric Biggers <ebiggers3@...il.com> wrote:
> From: Eric Biggers <ebiggers@...gle.com>
>
> This is a second attempt to fix the bug found by syzkaller where the
> ptrace syscall can be used to set invalid bits in a task's FPU state.
> I also found that an equivalent bug was reachable using the sigreturn
> syscall, so the first patch fixes the bug in both cases.
>
> The other two patches start validating the other parts of the
> xstate_header and make it so that invalid FPU states can no longer be
> abused to leak the FPU registers of other processes.
>
> Eric Biggers (3):
>   x86/fpu: don't let userspace set bogus xcomp_bv
>   x86/fpu: tighten validation of user-supplied xstate_header
>   x86/fpu: reinitialize FPU registers if restoring FPU state fails

This series looks sensible to me! Thanks for getting this fixed up.

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

-Kees

>
>  arch/x86/include/asm/fpu/internal.h | 29 ++++++++++++++++++++---------
>  arch/x86/include/asm/fpu/xstate.h   | 19 +++++++++++++++++++
>  arch/x86/kernel/fpu/core.c          | 16 ++++++++++++++++
>  arch/x86/kernel/fpu/regset.c        | 20 +++++++++-----------
>  arch/x86/kernel/fpu/signal.c        | 15 +++++++++++----
>  arch/x86/kernel/fpu/xstate.c        | 27 ++++++++++-----------------
>  6 files changed, 85 insertions(+), 41 deletions(-)
>
> --
> 2.14.1.690.gbb1197296e-goog
>



-- 
Kees Cook
Pixel Security