linux-kernel - [patch 38/41] x86/fpu: Mask PKRU from kernel XRSTOR[S] operations

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Message-Id: <20210611163115.112228696@linutronix.de>
Date:   Fri, 11 Jun 2021 18:16:01 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: [patch 38/41] x86/fpu: Mask PKRU from kernel XRSTOR[S] operations

As the PKRU state is managed seperately 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>
---
V4: New patch
---
 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(-)

--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -281,7 +281,7 @@ static inline void xsave_to_kernel_booti
  */
 static inline void xrstor_from_kernel_booting(struct xregs_state *xstate)
 {
-	u64 mask = -1;
+	u64 mask = xfeatures_mask_fpstate();
 	u32 lmask = mask;
 	u32 hmask = mask >> 32;
 	int err;
@@ -408,7 +408,7 @@ extern void __restore_fpregs_from_fpstat
 
 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);
--- 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
 	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))
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -60,6 +60,7 @@ static short xsave_cpuid_features[] __in
  * 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};
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -65,7 +65,7 @@ EXPORT_SYMBOL_GPL(ex_handler_fault);
 	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);