linux-kernel - [tip:x86/urgent] x86/fpu: Set the xcomp

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Date:   Mon, 23 Jan 2017 01:43:00 -0800
From:   tip-bot for Kevin Hao <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, hpa@...or.com, fenghua.yu@...el.com,
        jpoimboe@...hat.com, haokexin@...il.com, mingo@...nel.org,
        luto@...nel.org, yu-cheng.yu@...el.com, riel@...hat.com,
        dave.hansen@...ux.intel.com, bp@...en8.de, brgerst@...il.com,
        dvlasenk@...hat.com, linux-kernel@...r.kernel.org, oleg@...hat.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        quentin.casasnovas@...cle.com
Subject: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a XSAVES
 area

Commit-ID:  4c833368f0bf748d4147bf301b1f95bc8eccb3c0
Gitweb:     http://git.kernel.org/tip/4c833368f0bf748d4147bf301b1f95bc8eccb3c0
Author:     Kevin Hao <haokexin@...il.com>
AuthorDate: Sun, 22 Jan 2017 16:50:23 +0800
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Mon, 23 Jan 2017 10:40:18 +0100

x86/fpu: Set the xcomp_bv when we fake up a XSAVES area

I got the following calltrace on a Apollo Lake SoC with 32-bit kernel:

  WARNING: CPU: 2 PID: 261 at arch/x86/include/asm/fpu/internal.h:363 fpu__restore+0x1f5/0x260
  [...]
  Hardware name: Intel Corp. Broxton P/NOTEBOOK, BIOS APLIRVPA.X64.0138.B35.1608091058 08/09/2016
  Call Trace:
   dump_stack()
   __warn()
   ? fpu__restore()
   warn_slowpath_null()
   fpu__restore()
   __fpu__restore_sig()
   fpu__restore_sig()
   restore_sigcontext.isra.9()
   sys_sigreturn()
   do_int80_syscall_32()
   entry_INT80_32()

The reason is that a #GP occurs when executing XRSTORS. The root cause
is that we forget to set the xcomp_bv when we fake up the XSAVES area
in the copyin_to_xsaves() function.

Signed-off-by: Kevin Hao <haokexin@...il.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@...cle.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@...el.com>
Link: http://lkml.kernel.org/r/1485075023-30161-1-git-send-email-haokexin@gmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/kernel/fpu/xstate.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 1d77704..e287b90 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1070,6 +1070,7 @@ int copyin_to_xsaves(const void *kbuf, const void __user *ubuf,
 	 * Add back in the features that came in from userspace:
 	 */
 	xsave->header.xfeatures |= xfeatures;
+	xsave->header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT | xsave->header.xfeatures;
 
 	return 0;
 }