[tip:x86/urgent] x86/fpu/xstate: Fix xcomp_bv in XSAVES header

From: tip-bot for Yu-cheng Yu
Date: Tue Jan 24 2017 - 03:47:11 EST

Commit-ID: dffba9a31c7769be3231c420d4b364c92ba3f1ac
Gitweb: http://git.kernel.org/tip/dffba9a31c7769be3231c420d4b364c92ba3f1ac
Author: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
AuthorDate: Mon, 23 Jan 2017 14:54:44 -0800
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
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 <haokexin@xxxxxxxxx>
Reported-by: Joakim Tjernlund <Joakim.Tjernlund@xxxxxxxxxxxx>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: haokexin@xxxxxxxxx
Link: http://lkml.kernel.org/r/1485212084-4418-1-git-send-email-yu-cheng.yu@xxxxxxxxx
[ Combined it with 4c833368f0bf. ]
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
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;