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

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  [PATCH] x86/fpu/xstate: Fix xcomp_bv in XSAVES header Yu-cheng Yu <yu-cheng.yu@intel.com> - 2017-01-24 00:10 +0100
    Re: [PATCH] x86/fpu/xstate: Fix xcomp_bv in XSAVES header Ingo Molnar <mingo@kernel.org> - 2017-01-24 09:20 +0100
    [tip:x86/urgent] x86/fpu/xstate: Fix xcomp_bv in XSAVES header tip-bot for Yu-cheng Yu <tipbot@zytor.com> - 2017-01-24 09:50 +0100

#1565358 — [PATCH] 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: b22cbe404a9cc3c7949e380fa1861e31934c8978, 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
others:

	https://bugzilla.kernel.org/show_bug.cgi?id=190061

Fix it by setting xcomp_bv correctly.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reported-by: Joakim Tjernlund <Joakim.Tjernlund@infinera.com>
---
 arch/x86/kernel/fpu/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index c289e2f..e540dc1 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>
@@ -235,7 +236,8 @@ 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))
 		fpstate_init_fxstate(&state->fxsave);
-- 
1.9.1

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#1565641

* Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:

> 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: b22cbe404a9cc3c7949e380fa1861e31934c8978, 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
> others:
> 
> 	https://bugzilla.kernel.org/show_bug.cgi?id=190061
> 
> Fix it by setting xcomp_bv correctly.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Reported-by: Joakim Tjernlund <Joakim.Tjernlund@infinera.com>
> ---
>  arch/x86/kernel/fpu/core.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> index c289e2f..e540dc1 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>
> @@ -235,7 +236,8 @@ 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;

Ok, I have applied this - but it would be cleaner to go one step further and add a 
fpstate_init_xstate() method that does this in xstate.c and hides the details from 
arch/x86/kernel/fpu/core.c.

Similar to how the FX-state initialization is done today:

>  	if (static_cpu_has(X86_FEATURE_FXSR))
>  		fpstate_init_fxstate(&state->fxsave);

Thanks,

	Ingo

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#1565710 — [tip:x86/urgent] x86/fpu/xstate: Fix xcomp_bv in XSAVES header

Commit-ID:  dffba9a31c7769be3231c420d4b364c92ba3f1ac
Gitweb:     http://git.kernel.org/tip/dffba9a31c7769be3231c420d4b364c92ba3f1ac
Author:     Yu-cheng Yu <yu-cheng.yu@intel.com>
AuthorDate: Mon, 23 Jan 2017 14:54:44 -0800
Committer:  Ingo Molnar <mingo@kernel.org>
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
others:

	https://bugzilla.kernel.org/show_bug.cgi?id=190061

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
operation.

Reported-by: Kevin Hao <haokexin@gmail.com>
Reported-by: Joakim Tjernlund <Joakim.Tjernlund@infinera.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: haokexin@gmail.com
Link: http://lkml.kernel.org/r/1485212084-4418-1-git-send-email-yu-cheng.yu@intel.com
[ Combined it with 4c833368f0bf. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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))
 		fpstate_init_fxstate(&state->fxsave);
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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