x86/fpu: Rework restore_regs_from_fpstate()

xfeatures_mask_fpstate() is no longer valid when dynamically enabled
features come into play.

Rework restore_regs_from_fpstate() so it takes a constant mask which will
then be applied against the maximum feature set so that the restore
operation brings all features which are not in the xsave buffer xfeature
bitmap into init state.

This ensures that if the previous task used a dynamically enabled feature
that the task which restores has all unused components properly initialized.

Cleanup the last user of xfeatures_mask_fpstate() as well and remove it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.461348278@linutronix.de

3 files changed, 16 insertions, 9 deletions

diff --git a/arch/x86/kernel/fpu/context.h b/arch/x86/kernel/fpu/context.h
index f8f510519688..a06ebf315d83 100644
--- a/arch/x86/kernel/fpu/context.h
+++ b/arch/x86/kernel/fpu/context.h
@@ -61,8 +61,6 @@ static inline void fpregs_restore_userregs(void)
 		return;
 
 	if (!fpregs_state_valid(fpu, cpu)) {
-		u64 mask;
-
 		/*
 		 * This restores _all_ xstate which has not been
 		 * established yet.
@@ -72,9 +70,7 @@ static inline void fpregs_restore_userregs(void)
 		 * flush_thread(). So it is excluded because it might be
 		 * not up to date in current->thread.fpu.xsave state.
 		 */
-		mask = xfeatures_mask_restore_user() |
-			xfeatures_mask_supervisor();
-		restore_fpregs_from_fpstate(fpu->fpstate, mask);
+		restore_fpregs_from_fpstate(fpu->fpstate, XFEATURE_MASK_FPSTATE);
 
 		fpregs_activate(fpu);
 		fpu->last_cpu = cpu;
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 5acc077cb9f1..0fb9defaba47 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -150,6 +150,17 @@ void restore_fpregs_from_fpstate(struct fpstate *fpstate, u64 mask)
 	}
 
 	if (use_xsave()) {
+		/*
+		 * Restoring state always needs to modify all features
+		 * which are in @mask even if the current task cannot use
+		 * extended features.
+		 *
+		 * So fpstate->xfeatures cannot be used here, because then
+		 * a feature for which the task has no permission but was
+		 * used by the previous task would not go into init state.
+		 */
+		mask = fpu_kernel_cfg.max_features & mask;
+
 		os_xrstor(&fpstate->regs.xsave, mask);
 	} else {
 		if (use_fxsr())
@@ -161,7 +172,7 @@ void restore_fpregs_from_fpstate(struct fpstate *fpstate, u64 mask)
 
 void fpu_reset_from_exception_fixup(void)
 {
-	restore_fpregs_from_fpstate(&init_fpstate, xfeatures_mask_fpstate());
+	restore_fpregs_from_fpstate(&init_fpstate, XFEATURE_MASK_FPSTATE);
 }
 
 #if IS_ENABLED(CONFIG_KVM)
@@ -179,7 +190,7 @@ void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask)
 	}
 
 	if (rstor) {
-		restore_mask &= xfeatures_mask_fpstate();
+		restore_mask &= XFEATURE_MASK_FPSTATE;
 		restore_fpregs_from_fpstate(rstor->fpstate, restore_mask);
 	}
 
@@ -518,7 +529,7 @@ void fpu__clear_user_states(struct fpu *fpu)
 	}
 
 	/* Reset user states in registers. */
-	restore_fpregs_from_init_fpstate(xfeatures_mask_restore_user());
+	restore_fpregs_from_init_fpstate(XFEATURE_MASK_USER_RESTORE);
 
 	/*
 	 * Now all FPU registers have their desired values.  Inform the FPU
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 9f92abd230db..cbba3812a160 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -344,7 +344,7 @@ static void __init print_xstate_offset_size(void)
  */
 static __init void os_xrstor_booting(struct xregs_state *xstate)
 {
-	u64 mask = xfeatures_mask_fpstate();
+	u64 mask = fpu_kernel_cfg.max_features & XFEATURE_MASK_FPSTATE;
 	u32 lmask = mask;
 	u32 hmask = mask >> 32;
 	int err;