Subject: [RFC PATCH 18/25] powerpc/book3s64/pkeys: Don't update SPRN_AMR when in kernel mode.

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 27 Apr 2020 13:34:59 +0530

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

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 arch/powerpc/include/asm/book3s/64/kup.h | 27 +++++++++
 arch/powerpc/include/asm/pkeys.h         |  2 -
 arch/powerpc/include/asm/processor.h     |  5 --
 arch/powerpc/kernel/process.c            |  4 --
 arch/powerpc/kernel/traps.c              |  6 --
 arch/powerpc/mm/book3s64/pkeys.c         | 73 ++++--------------------
 6 files changed, 39 insertions(+), 78 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/kup.h b/arch/powerpc/include/asm/book3s/64/kup.h
index 717c2c4d3681..6a706e6fef59 100644
--- a/arch/powerpc/include/asm/book3s/64/kup.h
+++ b/arch/powerpc/include/asm/book3s/64/kup.h
@@ -158,6 +158,33 @@
 #include <asm/mmu.h>
 #include <asm/ptrace.h>
 
+extern u64 default_uamor;
+extern u64 default_amr;
+extern u64 default_iamr;
+
+/*
+ * 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->kuap;
+	return AMR_KUAP_BLOCKED;
+}
+
+static inline u64 current_thread_iamr(void)
+{
+	if (current->thread.regs)
+		return current->thread.regs->kuep;
+	return AMR_KUEP_BLOCKED;
+}
+
+static inline u64 read_uamor(void)
+{
+	return default_uamor;
+}
+
 static inline void kuap_restore_amr(struct pt_regs *regs, bool to_user)
 {
 	if (!mmu_has_feature(MMU_FTR_PKEY) && to_user)
diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index cd1a03044814..b1d448c53209 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h
@@ -12,8 +12,6 @@
 #include <asm/firmware.h>
 
 extern int max_pkey;
-extern u64 default_uamor;
-extern u64 default_amr;
 extern u32 reserved_allocation_mask; /* bits set for reserved keys */
 
 #define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | \
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index eedcbfb9a6ff..3cef707b27c7 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -234,11 +234,6 @@ 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;
-	unsigned long	uamor;
-#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 9660bab1d99d..17f65a2738bc 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -585,7 +585,6 @@ 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)
@@ -1097,8 +1096,6 @@ 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,
@@ -1139,7 +1136,6 @@ 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 3fca22276bb1..a47fb49b7af8 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -348,12 +348,6 @@ 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 42ca7aa09d5b..2484d8502499 100644
--- a/arch/powerpc/mm/book3s64/pkeys.c
+++ b/arch/powerpc/mm/book3s64/pkeys.c
@@ -21,7 +21,7 @@ int  max_pkey;			/* Maximum key value supported */
 u32  reserved_allocation_mask;
 static u32  initial_allocation_mask;   /* Bits set for the initially allocated keys */
 u64 default_amr;
-static u64 default_iamr;
+u64 default_iamr;
 /* Allow all keys to be modified by default */
 u64 default_uamor = ~0x0UL;
 /*
@@ -264,40 +264,17 @@ void pkey_mm_init(struct mm_struct *mm)
 	mm->context.execute_only_pkey = execute_only_key;
 }
 
-static inline u64 read_amr(void)
+static inline void update_current_thread_amr(u64 value)
 {
-	return mfspr(SPRN_AMR);
+	current->thread.regs->kuap = value;
 }
 
-static inline void write_amr(u64 value)
-{
-	mtspr(SPRN_AMR, value);
-}
-
-static inline u64 read_iamr(void)
-{
-	if (static_branch_unlikely(&execute_pkey_disabled))
-		return 0x0UL;
-
-	return mfspr(SPRN_IAMR);
-}
-
-static inline void write_iamr(u64 value)
+static inline void update_current_thread_iamr(u64 value)
 {
 	if (static_branch_unlikely(&execute_pkey_disabled))
 		return;
 
-	mtspr(SPRN_IAMR, value);
-}
-
-static inline u64 read_uamor(void)
-{
-	return mfspr(SPRN_UAMOR);
-}
-
-static inline void write_uamor(u64 value)
-{
-	mtspr(SPRN_UAMOR, value);
+	current->thread.regs->kuep = value;
 }
 
 static bool is_pkey_enabled(int pkey)
@@ -314,20 +291,21 @@ static bool is_pkey_enabled(int pkey)
 	return !!(uamor_pkey_bits);
 }
 
+/*  FIXME!! what happens to other threads AMR value? */
 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);
 }
 
 /*
@@ -360,33 +338,6 @@ 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();
-	thread->uamor = read_uamor();
-}
-
-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);
-	if (old_thread->uamor != new_thread->uamor)
-		write_uamor(new_thread->uamor);
-}
-
 int execute_only_pkey(struct mm_struct *mm)
 {
 	if (static_branch_likely(&execute_pkey_disabled))
@@ -440,10 +391,10 @@ static bool pkey_access_permitted(int pkey, bool write, bool execute)
 		return true;
 
 	pkey_shift = pkeyshift(pkey);
-	if (execute && !(read_iamr() & (IAMR_EX_BIT << pkey_shift)))
+	if (execute && !(current_thread_iamr() & (IAMR_EX_BIT << pkey_shift)))
 		return true;
 
-	amr = read_amr(); /* Delay reading amr until absolutely needed */
+	amr = current_thread_amr();
 	return ((!write && !(amr & (AMR_RD_BIT << pkey_shift))) ||
 		(write &&  !(amr & (AMR_WR_BIT << pkey_shift))));
 }
-- 
2.25.3