linux-kernel - [tip: x86/fpu] x86/fpu: Mask PKRU from kernel XRSTOR[S] operations

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Date:   Wed, 23 Jun 2021 22:08:59 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...e.de>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/fpu] x86/fpu: Mask PKRU from kernel XRSTOR[S] operations

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     30a304a138738d71a09c730ca8044e9662de0dbf
Gitweb:        https://git.kernel.org/tip/30a304a138738d71a09c730ca8044e9662de0dbf
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Wed, 23 Jun 2021 14:02:20 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Wed, 23 Jun 2021 19:47:35 +02:00

x86/fpu: Mask PKRU from kernel XRSTOR[S] operations

As the PKRU state is managed separately restoring it from the xstate
buffer would be counterproductive as it might either restore a stale
value or reinit the PKRU state to 0.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Borislav Petkov <bp@...e.de>
Link: https://lkml.kernel.org/r/20210623121456.606745195@linutronix.de
---
 arch/x86/include/asm/fpu/internal.h |  4 ++--
 arch/x86/include/asm/fpu/xstate.h   | 10 ++++++++++
 arch/x86/kernel/fpu/xstate.c        |  1 +
 arch/x86/mm/extable.c               |  2 +-
 4 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 5217743..2a484f5 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -259,7 +259,7 @@ static inline void fxsave(struct fxregs_state *fx)
  */
 static inline void os_xrstor_booting(struct xregs_state *xstate)
 {
-	u64 mask = -1;
+	u64 mask = xfeatures_mask_fpstate();
 	u32 lmask = mask;
 	u32 hmask = mask >> 32;
 	int err;
@@ -388,7 +388,7 @@ extern void __restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask)
 
 static inline void restore_fpregs_from_fpstate(union fpregs_state *fpstate)
 {
-	__restore_fpregs_from_fpstate(fpstate, -1);
+	__restore_fpregs_from_fpstate(fpstate, xfeatures_mask_fpstate());
 }
 
 extern int copy_fpstate_to_sigframe(void __user *buf, void __user *fp, int size);
diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index 4ff4a00..109dfcc 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -111,6 +111,16 @@ static inline u64 xfeatures_mask_restore_user(void)
 	return xfeatures_mask_all & XFEATURE_MASK_USER_RESTORE;
 }
 
+/*
+ * Like xfeatures_mask_restore_user() but additionally restors the
+ * supported supervisor states.
+ */
+static inline u64 xfeatures_mask_fpstate(void)
+{
+	return xfeatures_mask_all & \
+		(XFEATURE_MASK_USER_RESTORE | XFEATURE_MASK_SUPERVISOR_SUPPORTED);
+}
+
 static inline u64 xfeatures_mask_independent(void)
 {
 	if (!boot_cpu_has(X86_FEATURE_ARCH_LBR))
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 9fd124a..21a10a6 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -60,6 +60,7 @@ static short xsave_cpuid_features[] __initdata = {
  * XSAVE buffer, both supervisor and user xstates.
  */
 u64 xfeatures_mask_all __ro_after_init;
+EXPORT_SYMBOL_GPL(xfeatures_mask_all);
 
 static unsigned int xstate_offsets[XFEATURE_MAX] __ro_after_init =
 	{ [ 0 ... XFEATURE_MAX - 1] = -1};
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 2c5cccd..e1664e9 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -65,7 +65,7 @@ __visible bool ex_handler_fprestore(const struct exception_table_entry *fixup,
 	WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.",
 		  (void *)instruction_pointer(regs));
 
-	__restore_fpregs_from_fpstate(&init_fpstate, -1);
+	__restore_fpregs_from_fpstate(&init_fpstate, xfeatures_mask_fpstate());
 	return true;
 }
 EXPORT_SYMBOL_GPL(ex_handler_fprestore);