linux-kernel - [PATCH 3/4] x86/fpu/xstate: Fix fpstate

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Date:	Mon, 11 Jul 2016 09:18:56 -0700
From:	"Fenghua Yu" <fenghua.yu@...el.com>
To:	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <h.peter.anvin@...el.com>,
	"Dave Hansen" <dave.hansen@...el.com>,
	"Ravi V Shankar" <ravi.v.shankar@...el.com>
Cc:	Yu-cheng Yu <yu-cheng.yu@...el.com>,
	"Fenghua Yu" <fenghua.yu@...el.com>, "x86" <x86@...nel.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>
Subject: [PATCH 3/4] x86/fpu/xstate: Fix fpstate_init() for XRSTORS

From: Yu-cheng Yu <yu-cheng.yu@...el.com>

In XSAVES mode if fpstate_init() is used to initialize a
task's extended state area, xsave.header.xcomp_bv[63] must
be set. Otherwise, when the task is scheduled, a warning is
triggered from copy_kernel_to_xregs().

One such test case is: setting an invalid extended state
through PTRACE. When xstateregs_set() rejects the syscall
and re-initializes the task's extended state area. This triggers
the warning mentioned above.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
Reviewed-by: Dave Hansen <dave.hansen@...el.com>
---
 arch/x86/include/asm/fpu/types.h | 6 ++++++
 arch/x86/kernel/fpu/core.c       | 8 ++++++++
 2 files changed, 14 insertions(+)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 12dd648..48df486 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -232,6 +232,12 @@ struct xstate_header {
 } __attribute__((packed));
 
 /*
+ * xstate_header.xcomp_bv[63] indicates that the extended_state_area
+ * is in compacted format.
+ */
+#define XCOMP_BV_COMPACTED_FORMAT ((u64)1 << 63)
+
+/*
  * This is our most modern FPU state format, as saved by the XSAVE
  * and restored by the XRSTOR instructions.
  *
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index c759bd0..3fc03a0 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -8,6 +8,7 @@
 #include <asm/fpu/internal.h>
 #include <asm/fpu/regset.h>
 #include <asm/fpu/signal.h>
+#include <asm/fpu/types.h>
 #include <asm/traps.h>
 
 #include <linux/hardirq.h>
@@ -229,6 +230,13 @@ void fpstate_init(union fpregs_state *state)
 
 	memset(state, 0, fpu_kernel_xstate_size);
 
+	/*
+	 * XRSTORS requires that this bit is set in xcomp_bv, or
+	 * 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;
+
 	if (static_cpu_has(X86_FEATURE_FXSR))
 		fpstate_init_fxstate(&state->fxsave);
 	else
-- 
2.5.0