Re: [tip:x86/urgent] x86/fpu/xstate: Fix xcomp_bv in XSAVES header

[Yu-cheng Yu <yu-cheng.yu@intel.com>]

On Tue, Jan 24, 2017 at 12:46:17AM -0800, tip-bot for Yu-cheng Yu wrote:
> Commit-ID:  dffba9a31c7769be3231c420d4b364c92ba3f1ac
> Gitweb:     http://git.kernel.org/tip/dffba9a31c7769be3231c420d4b364c92ba3f1ac
> Author:     Yu-cheng Yu <yu-cheng.yu@intel.com>
> AuthorDate: Mon, 23 Jan 2017 14:54:44 -0800
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Tue, 24 Jan 2017 09:04:48 +0100
> 
> x86/fpu/xstate: Fix xcomp_bv in XSAVES header
> 
> The compacted-format XSAVES area is determined at boot time and
> never changed after.  The field xsave.header.xcomp_bv indicates
> which components are in the fixed XSAVES format.
> 
> In fpstate_init() we did not set xcomp_bv to reflect the XSAVES
> format since at the time there is no valid data.
> 
> However, after we do copy_init_fpstate_to_fpregs() in fpu__clear(),
> as in commit:
> 
>   b22cbe404a9c x86/fpu: Fix invalid FPU ptrace state after execve()
> 
> and when __fpu_restore_sig() does fpu__restore() for a COMPAT-mode
> app, a #GP occurs.  This can be easily triggered by doing valgrind on
> a COMPAT-mode "Hello World," as reported by Joakim Tjernlund and
> others:
> 
> 	https://bugzilla.kernel.org/show_bug.cgi?id=190061
> 
> Fix it by setting xcomp_bv correctly.
> 

Please consider pulling this into the stable tree because my previous
patch in commit: 

  b22cbe404a9c x86/fpu: Fix invalid FPU ptrace state after execve()

exposes the same issue in the stable tree.

Thanks,
Yu-cheng