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Date: Thu, 21 Sep 2017 16:21:47 -0400
From: Rik van Riel <>
To: Eric Biggers <>,
Cc:,, Andy
 Lutomirski <>, Dave Hansen <>,
 Dmitry Vyukov <>, Fenghua Yu <>, Ingo
 Molnar <>, Kevin Hao <>, Oleg Nesterov
 <>, Wanpeng Li <>, Yu-cheng Yu
 <>, Michael Halcrow <>, Eric
 Biggers <>
Subject: Re: [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 <>
> 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 <>
> Acked-by: Dave Hansen <>
> Cc: Andy Lutomirski <>
> Cc: Dmitry Vyukov <>
> Cc: Fenghua Yu <>
> Cc: Ingo Molnar <>
> Cc: Kevin Hao <>
> Cc: Oleg Nesterov <>
> Cc: Wanpeng Li <>
> Cc: Yu-cheng Yu <>
> Signed-off-by: Eric Biggers <>
Reviewed-by: Rik van Riel <>

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