linux-kernel - [PATCH AUTOSEL for 4.9 33/54] x86/fpu: Set the xcomp

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Message-ID: <20171122222344.19782-33-alexander.levin@verizon.com>
Date:   Wed, 22 Nov 2017 22:23:59 +0000
From:   alexander.levin@...izon.com
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Kevin Hao <haokexin@...il.com>, Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "Fenghua Yu" <fenghua.yu@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Oleg Nesterov" <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Quentin Casasnovas" <quentin.casasnovas@...cle.com>,
        Rik van Riel <riel@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Ingo Molnar <mingo@...nel.org>, alexander.levin@...izon.com
Subject: [PATCH AUTOSEL for 4.9 33/54] x86/fpu: Set the xcomp_bv when we fake
 up a XSAVES area

From: Kevin Hao <haokexin@...il.com>

[ Upstream commit 4c833368f0bf748d4147bf301b1f95bc8eccb3c0 ]

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>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
---
 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 095ef7ddd6ae..abfbb61b18b8 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1077,6 +1077,7 @@ 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;
 }
-- 
2.11.0