x86/fpu: Use pkru_write_default() in copy_init_fpstate_to_fpregs()

There is no point in using copy_init_pkru_to_fpregs() which in turn calls
write_pkru(). write_pkru() tries to fiddle with the task's xstate buffer
for nothing because the XRSTOR[S](init_fpstate) just cleared the xfeature
flag in the xstate header which makes get_xsave_addr() fail.

It's a useless exercise anyway because the reinitialization activates the
FPU so before the task's xstate buffer can be used again a XRSTOR[S] must
happen which in turn dumps the PKRU value.

Get rid of the now unused copy_init_pkru_to_fpregs().
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121455.732508792@linutronix.de

arch/x86/include/asm/pkeys.h

@@ -124,7 +124,6 @@ extern int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 		unsigned long init_val);
 extern int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 		unsigned long init_val);
-extern void copy_init_pkru_to_fpregs(void);
 
 static inline int vma_pkey(struct vm_area_struct *vma)
 {

arch/x86/kernel/fpu/core.c

@@ -311,8 +311,7 @@ static inline void restore_fpregs_from_init_fpstate(u64 features_mask)
 	else
 		frstor(&init_fpstate.fsave);
 
-	if (cpu_feature_enabled(X86_FEATURE_OSPKE))
-		copy_init_pkru_to_fpregs();
+	pkru_write_default();
 }
 
 /*

arch/x86/mm/pkeys.c

@@ -10,7 +10,6 @@
 
 #include <asm/cpufeature.h>             /* boot_cpu_has, ...            */
 #include <asm/mmu_context.h>            /* vma_pkey()                   */
-#include <asm/pkru.h>			/* read/write_pkru()		*/
 
 int __execute_only_pkey(struct mm_struct *mm)
 {
@@ -125,22 +124,6 @@ u32 init_pkru_value = PKRU_AD_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) |
 		      PKRU_AD_KEY(10) | PKRU_AD_KEY(11) | PKRU_AD_KEY(12) |
 		      PKRU_AD_KEY(13) | PKRU_AD_KEY(14) | PKRU_AD_KEY(15);
 
-/*
- * Called from the FPU code when creating a fresh set of FPU
- * registers.  This is called from a very specific context where
- * we know the FPU registers are safe for use and we can use PKRU
- * directly.
- */
-void copy_init_pkru_to_fpregs(void)
-{
-	u32 init_pkru_value_snapshot = READ_ONCE(init_pkru_value);
-	/*
-	 * Override the PKRU state that came from 'init_fpstate'
-	 * with the baseline from the process.
-	 */
-	write_pkru(init_pkru_value_snapshot);
-}
-
 static ssize_t init_pkru_read_file(struct file *file, char __user *user_buf,
 			     size_t count, loff_t *ppos)
 {

include/linux/pkeys.h

@@ -44,10 +44,6 @@ static inline bool arch_pkeys_enabled(void)
 	return false;
 }
 
-static inline void copy_init_pkru_to_fpregs(void)
-{
-}
-
 #endif /* ! CONFIG_ARCH_HAS_PKEYS */
 
 #endif /* _LINUX_PKEYS_H */