[tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a XSAVES area

tip-bot for Kevin Hao
2017-01-23T08:29:16Z

Commit-ID: 5fa356458b5c918bdf8307b070a3d74bc015d910
Gitweb: http://git.kernel.org/tip/5fa356458b5c918bdf8307b070a3d74bc015d910
Author: Kevin Hao <haokexin@gmail.com>
AuthorDate: Sun, 22 Jan 2017 16:50:23 +0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 23 Jan 2017 09:03:03 +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@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>
---
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;
}