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Date:   Tue, 24 Jan 2017 00:46:17 -0800
From:   tip-bot for Yu-cheng Yu <>
Subject: [tip:x86/urgent] x86/fpu/xstate: Fix xcomp_bv in XSAVES header

Commit-ID:  dffba9a31c7769be3231c420d4b364c92ba3f1ac
Author:     Yu-cheng Yu <>
AuthorDate: Mon, 23 Jan 2017 14:54:44 -0800
Committer:  Ingo Molnar <>
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

Fix it by setting xcomp_bv correctly.

This patch also moves the xcomp_bv initialization to the proper
place, which was in copyin_to_xsaves() as of:

  4c833368f0bf x86/fpu: Set the xcomp_bv when we fake up a XSAVES area

which fixed the bug too, but it's more efficient and cleaner to
initialize things once per boot, not for every signal handling

Reported-by: Kevin Hao <>
Reported-by: Joakim Tjernlund <>
Signed-off-by: Yu-cheng Yu <>
Cc: Andy Lutomirski <>
Cc: Borislav Petkov <>
Cc: Dave Hansen <>
Cc: Fenghua Yu <>
Cc: Linus Torvalds <>
Cc: Peter Zijlstra <>
Cc: Ravi V. Shankar <>
Cc: Thomas Gleixner <>
[ Combined it with 4c833368f0bf. ]
Signed-off-by: Ingo Molnar <>
 arch/x86/kernel/fpu/core.c   | 4 +++-
 arch/x86/kernel/fpu/xstate.c | 1 -
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index e4e97a5..de72344 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -9,6 +9,7 @@
 #include <asm/fpu/regset.h>
 #include <asm/fpu/signal.h>
 #include <asm/fpu/types.h>
+#include <asm/fpu/xstate.h>
 #include <asm/traps.h>
 #include <linux/hardirq.h>
@@ -183,7 +184,8 @@ void fpstate_init(union fpregs_state *state)
 	 * it will #GP. Make sure it is replaced after the memset().
 	if (static_cpu_has(X86_FEATURE_XSAVES))
-		state->xsave.header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT;
+		state->xsave.header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT |
+					       xfeatures_mask;
 	if (static_cpu_has(X86_FEATURE_FXSR))
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index e287b90..1d77704 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1070,7 +1070,6 @@ 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;

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