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Subject[PATCH 4.9 066/109] x86/fpu: Set the xcomp_bv when we fake up a XSAVES area
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kevin Hao <haokexin@gmail.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@gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/1485075023-30161-1-git-send-email-haokexin@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/fpu/xstate.c | 1 +
1 file changed, 1 insertion(+)

--- 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, c
* 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;
}

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