powerpc: store and restore the pkey state across context switches

Store and restore the AMR, IAMR and UAMOR register state of the task
before scheduling out and after scheduling in, respectively.
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/mmu_context.h

@@ -195,6 +195,9 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 
 #ifndef CONFIG_PPC_MEM_KEYS
 #define pkey_mm_init(mm)
+#define thread_pkey_regs_save(thread)
+#define thread_pkey_regs_restore(new_thread, old_thread)
+#define thread_pkey_regs_init(thread)
 #endif /* CONFIG_PPC_MEM_KEYS */
 
 #endif /* __KERNEL__ */

arch/powerpc/include/asm/pkeys.h

@@ -139,4 +139,8 @@ static inline int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 }
 
 extern void pkey_mm_init(struct mm_struct *mm);
+extern void thread_pkey_regs_save(struct thread_struct *thread);
+extern void thread_pkey_regs_restore(struct thread_struct *new_thread,
+				     struct thread_struct *old_thread);
+extern void thread_pkey_regs_init(struct thread_struct *thread);
 #endif /*_ASM_POWERPC_KEYS_H */

arch/powerpc/include/asm/processor.h

@@ -309,6 +309,11 @@ struct thread_struct {
 	struct thread_vr_state ckvr_state; /* Checkpointed VR state */
 	unsigned long	ckvrsave; /* Checkpointed VRSAVE */
 #endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
+#ifdef CONFIG_PPC_MEM_KEYS
+	unsigned long	amr;
+	unsigned long	iamr;
+	unsigned long	uamor;
+#endif
 #ifdef CONFIG_KVM_BOOK3S_32_HANDLER
 	void*		kvm_shadow_vcpu; /* KVM internal data */
 #endif /* CONFIG_KVM_BOOK3S_32_HANDLER */

arch/powerpc/kernel/process.c

@@ -42,6 +42,7 @@
 #include <linux/hw_breakpoint.h>
 #include <linux/uaccess.h>
 #include <linux/elf-randomize.h>
+#include <linux/pkeys.h>
 
 #include <asm/pgtable.h>
 #include <asm/io.h>
@@ -1103,6 +1104,8 @@ static inline void save_sprs(struct thread_struct *t)
 		t->tar = mfspr(SPRN_TAR);
 	}
 #endif
+
+	thread_pkey_regs_save(t);
 }
 
 static inline void restore_sprs(struct thread_struct *old_thread,
@@ -1142,6 +1145,8 @@ static inline void restore_sprs(struct thread_struct *old_thread,
 	    old_thread->tidr != new_thread->tidr)
 		mtspr(SPRN_TIDR, new_thread->tidr);
 #endif
+
+	thread_pkey_regs_restore(new_thread, old_thread);
 }
 
 #ifdef CONFIG_PPC_BOOK3S_64
@@ -1867,6 +1872,8 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp)
 	current->thread.tm_tfiar = 0;
 	current->thread.load_tm = 0;
 #endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
+
+	thread_pkey_regs_init(&current->thread);
 }
 EXPORT_SYMBOL(start_thread);
 

arch/powerpc/mm/pkeys.c

@@ -12,6 +12,8 @@ DEFINE_STATIC_KEY_TRUE(pkey_disabled);
 bool pkey_execute_disable_supported;
 int  pkeys_total;		/* Total pkeys as per device tree */
 u32  initial_allocation_mask;	/* Bits set for reserved keys */
+u64  pkey_amr_uamor_mask;	/* Bits in AMR/UMOR not to be touched */
+u64  pkey_iamr_mask;		/* Bits in AMR not to be touched */
 
 #define AMR_BITS_PER_PKEY 2
 #define AMR_RD_BIT 0x1UL
@@ -70,8 +72,16 @@ int pkey_initialize(void)
 	 * programming note.
 	 */
 	initial_allocation_mask = ~0x0;
-	for (i = 2; i < (pkeys_total - os_reserved); i++)
+
+	/* register mask is in BE format */
+	pkey_amr_uamor_mask = ~0x0ul;
+	pkey_iamr_mask = ~0x0ul;
+
+	for (i = 2; i < (pkeys_total - os_reserved); i++) {
 		initial_allocation_mask &= ~(0x1 << i);
+		pkey_amr_uamor_mask &= ~(0x3ul << pkeyshift(i));
+		pkey_iamr_mask &= ~(0x1ul << pkeyshift(i));
+	}
 	return 0;
 }
 
@@ -206,3 +216,43 @@ int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 	init_amr(pkey, new_amr_bits);
 	return 0;
 }
+
+void thread_pkey_regs_save(struct thread_struct *thread)
+{
+	if (static_branch_likely(&pkey_disabled))
+		return;
+
+	/*
+	 * TODO: Skip saving registers if @thread hasn't used any keys yet.
+	 */
+	thread->amr = read_amr();
+	thread->iamr = read_iamr();
+	thread->uamor = read_uamor();
+}
+
+void thread_pkey_regs_restore(struct thread_struct *new_thread,
+			      struct thread_struct *old_thread)
+{
+	if (static_branch_likely(&pkey_disabled))
+		return;
+
+	/*
+	 * TODO: Just set UAMOR to zero if @new_thread hasn't used any keys yet.
+	 */
+	if (old_thread->amr != new_thread->amr)
+		write_amr(new_thread->amr);
+	if (old_thread->iamr != new_thread->iamr)
+		write_iamr(new_thread->iamr);
+	if (old_thread->uamor != new_thread->uamor)
+		write_uamor(new_thread->uamor);
+}
+
+void thread_pkey_regs_init(struct thread_struct *thread)
+{
+	if (static_branch_likely(&pkey_disabled))
+		return;
+
+	write_amr(read_amr() & pkey_amr_uamor_mask);
+	write_iamr(read_iamr() & pkey_iamr_mask);
+	write_uamor(read_uamor() & pkey_amr_uamor_mask);
+}