[patch V2 48/52] x86/fpu: Mask PKRU from kernel XRSTOR[S] operations

Thomas Gleixner
2021-06-14T16:40:42Z

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@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(-)

--- 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);