Subject: [PATCH v6 14/22] powerpc/book3s64/pkeys: Don't update SPRN_AMR when in kernel mode.

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 25 Nov 2020 10:46:26 +0530

Now that kernel correctly store/restore userspace AMR/IAMR values, avoid
manipulating AMR and IAMR from the kernel on behalf of userspace.

Reviewed-by: Sandipan Das <[email-masked]>
Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 arch/powerpc/include/asm/book3s/64/kup.h | 21 +++++++++
 arch/powerpc/include/asm/processor.h     |  4 --
 arch/powerpc/kernel/process.c            |  4 --
 arch/powerpc/kernel/traps.c              |  6 ---
 arch/powerpc/mm/book3s64/pkeys.c         | 57 +++++-------------------
 5 files changed, 31 insertions(+), 61 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/kup.h b/arch/powerpc/include/asm/book3s/64/kup.h
index 4dbb2d53fd8f..47270596215b 100644
--- a/arch/powerpc/include/asm/book3s/64/kup.h
+++ b/arch/powerpc/include/asm/book3s/64/kup.h
@@ -175,6 +175,27 @@ DECLARE_STATIC_KEY_FALSE(uaccess_flush_key);
 #include <asm/mmu.h>
 #include <asm/ptrace.h>
 
+/*
+ * For kernel thread that doesn't have thread.regs return
+ * default AMR/IAMR values.
+ */
+static inline u64 current_thread_amr(void)
+{
+	if (current->thread.regs)
+		return current->thread.regs->amr;
+	return AMR_KUAP_BLOCKED;
+}
+
+static inline u64 current_thread_iamr(void)
+{
+	if (current->thread.regs)
+		return current->thread.regs->iamr;
+	return AMR_KUEP_BLOCKED;
+}
+#endif /* CONFIG_PPC_PKEY */
+
+#ifdef CONFIG_PPC_KUAP
+
 static inline void kuap_restore_user_amr(struct pt_regs *regs)
 {
 	if (!mmu_has_feature(MMU_FTR_PKEY))
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index c61c859b51a8..c3df3a420c92 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -230,10 +230,6 @@ 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;
-#endif
 #ifdef CONFIG_KVM_BOOK3S_32_HANDLER
 	void*		kvm_shadow_vcpu; /* KVM internal data */
 #endif /* CONFIG_KVM_BOOK3S_32_HANDLER */
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 98f7e9ec766f..5ffdac46a187 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -589,7 +589,6 @@ static void save_all(struct task_struct *tsk)
 		__giveup_spe(tsk);
 
 	msr_check_and_clear(msr_all_available);
-	thread_pkey_regs_save(&tsk->thread);
 }
 
 void flush_all_to_thread(struct task_struct *tsk)
@@ -1160,8 +1159,6 @@ 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,
@@ -1202,7 +1199,6 @@ static inline void restore_sprs(struct thread_struct *old_thread,
 		mtspr(SPRN_TIDR, new_thread->tidr);
 #endif
 
-	thread_pkey_regs_restore(new_thread, old_thread);
 }
 
 struct task_struct *__switch_to(struct task_struct *prev,
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 5006dcbe1d9f..419028d53fd6 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -347,12 +347,6 @@ static bool exception_common(int signr, struct pt_regs *regs, int code,
 
 	current->thread.trap_nr = code;
 
-	/*
-	 * Save all the pkey registers AMR/IAMR/UAMOR. Eg: Core dumps need
-	 * to capture the content, if the task gets killed.
-	 */
-	thread_pkey_regs_save(&current->thread);
-
 	return true;
 }
 
diff --git a/arch/powerpc/mm/book3s64/pkeys.c b/arch/powerpc/mm/book3s64/pkeys.c
index f47d11f2743d..f747d66cc87d 100644
--- a/arch/powerpc/mm/book3s64/pkeys.c
+++ b/arch/powerpc/mm/book3s64/pkeys.c
@@ -273,30 +273,17 @@ void __init setup_kuap(bool disabled)
 }
 #endif
 
-static inline u64 read_amr(void)
+static inline void update_current_thread_amr(u64 value)
 {
-	return mfspr(SPRN_AMR);
+	current->thread.regs->amr = value;
 }
 
-static inline void write_amr(u64 value)
-{
-	mtspr(SPRN_AMR, value);
-}
-
-static inline u64 read_iamr(void)
-{
-	if (!likely(pkey_execute_disable_supported))
-		return 0x0UL;
-
-	return mfspr(SPRN_IAMR);
-}
-
-static inline void write_iamr(u64 value)
+static inline void update_current_thread_iamr(u64 value)
 {
 	if (!likely(pkey_execute_disable_supported))
 		return;
 
-	mtspr(SPRN_IAMR, value);
+	current->thread.regs->iamr = value;
 }
 
 #ifdef CONFIG_PPC_MEM_KEYS
@@ -311,17 +298,17 @@ void pkey_mm_init(struct mm_struct *mm)
 static inline void init_amr(int pkey, u8 init_bits)
 {
 	u64 new_amr_bits = (((u64)init_bits & 0x3UL) << pkeyshift(pkey));
-	u64 old_amr = read_amr() & ~((u64)(0x3ul) << pkeyshift(pkey));
+	u64 old_amr = current_thread_amr() & ~((u64)(0x3ul) << pkeyshift(pkey));
 
-	write_amr(old_amr | new_amr_bits);
+	update_current_thread_amr(old_amr | new_amr_bits);
 }
 
 static inline void init_iamr(int pkey, u8 init_bits)
 {
 	u64 new_iamr_bits = (((u64)init_bits & 0x1UL) << pkeyshift(pkey));
-	u64 old_iamr = read_iamr() & ~((u64)(0x1ul) << pkeyshift(pkey));
+	u64 old_iamr = current_thread_iamr() & ~((u64)(0x1ul) << pkeyshift(pkey));
 
-	write_iamr(old_iamr | new_iamr_bits);
+	update_current_thread_iamr(old_iamr | new_iamr_bits);
 }
 
 /*
@@ -364,30 +351,6 @@ int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 	return 0;
 }
 
-void thread_pkey_regs_save(struct thread_struct *thread)
-{
-	if (!mmu_has_feature(MMU_FTR_PKEY))
-		return;
-
-	/*
-	 * TODO: Skip saving registers if @thread hasn't used any keys yet.
-	 */
-	thread->amr = read_amr();
-	thread->iamr = read_iamr();
-}
-
-void thread_pkey_regs_restore(struct thread_struct *new_thread,
-			      struct thread_struct *old_thread)
-{
-	if (!mmu_has_feature(MMU_FTR_PKEY))
-		return;
-
-	if (old_thread->amr != new_thread->amr)
-		write_amr(new_thread->amr);
-	if (old_thread->iamr != new_thread->iamr)
-		write_iamr(new_thread->iamr);
-}
-
 int execute_only_pkey(struct mm_struct *mm)
 {
 	return mm->context.execute_only_pkey;
@@ -436,9 +399,9 @@ static bool pkey_access_permitted(int pkey, bool write, bool execute)
 
 	pkey_shift = pkeyshift(pkey);
 	if (execute)
-		return !(read_iamr() & (IAMR_EX_BIT << pkey_shift));
+		return !(current_thread_iamr() & (IAMR_EX_BIT << pkey_shift));
 
-	amr = read_amr();
+	amr = current_thread_amr();
 	if (write)
 		return !(amr & (AMR_WR_BIT << pkey_shift));
 
-- 
2.28.0