powerpc/book3s64/kuap: Move UAMOR setup to key init function

UAMOR values are not application-specific. The kernel initializes
its value based on different reserved keys. Remove the thread-specific
UAMOR value and don't switch the UAMOR on context switch.

Move UAMOR initialization to key initialization code and remove
thread_struct.uamor because it is not used anymore.

Before commit: 4a4a5e5d2aad ("powerpc/pkeys: key allocation/deallocation must not change pkey registers")
we used to update uamor based on key allocation and free.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200709032946.881753-20-aneesh.kumar@linux.ibm.com

arch/powerpc/include/asm/book3s/64/pkeys.h

@@ -5,6 +5,8 @@
 
 #include <asm/book3s/64/hash-pkey.h>
 
+extern u64 __ro_after_init default_uamor;
+
 static inline u64 vmflag_to_pte_pkey_bits(u64 vm_flags)
 {
 	if (!mmu_has_feature(MMU_FTR_PKEY))

arch/powerpc/include/asm/processor.h

@@ -237,7 +237,6 @@ struct thread_struct {
 #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 */

arch/powerpc/kernel/ptrace/ptrace-view.c

@@ -488,14 +488,21 @@ static int pkey_active(struct task_struct *target, const struct user_regset *reg
 static int pkey_get(struct task_struct *target, const struct user_regset *regset,
 		    unsigned int pos, unsigned int count, void *kbuf, void __user *ubuf)
 {
+	int ret;
+
 	BUILD_BUG_ON(TSO(amr) + sizeof(unsigned long) != TSO(iamr));
-	BUILD_BUG_ON(TSO(iamr) + sizeof(unsigned long) != TSO(uamor));
 
 	if (!arch_pkeys_enabled())
 		return -ENODEV;
 
-	return user_regset_copyout(&pos, &count, &kbuf, &ubuf, &target->thread.amr,
-				   0, ELF_NPKEY * sizeof(unsigned long));
+	ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, &target->thread.amr,
+				  0, 2 * sizeof(unsigned long));
+	if (ret)
+		return ret;
+
+	ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, &default_uamor,
+				  2 * sizeof(unsigned long), 3 * sizeof(unsigned long));
+	return ret;
 }
 
 static int pkey_set(struct task_struct *target, const struct user_regset *regset,
@@ -517,9 +524,17 @@ static int pkey_set(struct task_struct *target, const struct user_regset *regset
 	if (ret)
 		return ret;
 
-	/* UAMOR determines which bits of the AMR can be set from userspace. */
-	target->thread.amr = (new_amr & target->thread.uamor) |
-			     (target->thread.amr & ~target->thread.uamor);
+	/*
+	 * UAMOR determines which bits of the AMR can be set from userspace.
+	 * UAMOR value 0b11 indicates that the AMR value can be modified
+	 * from userspace. If the kernel is using a specific key, we avoid
+	 * userspace modifying the AMR value for that key by masking them
+	 * via UAMOR 0b00.
+	 *
+	 * Pick the AMR values for the keys that kernel is using. This
+	 * will be indicated by the ~default_uamor bits.
+	 */
+	target->thread.amr = (new_amr & default_uamor) | (target->thread.amr & ~default_uamor);
 
 	return 0;
 }

arch/powerpc/kernel/smp.c

@@ -59,6 +59,7 @@
 #include <asm/asm-prototypes.h>
 #include <asm/cpu_has_feature.h>
 #include <asm/ftrace.h>
+#include <asm/kup.h>
 
 #ifdef DEBUG
 #include <asm/udbg.h>

arch/powerpc/mm/book3s64/hash_utils.c

@@ -1110,6 +1110,10 @@ void hash__early_init_mmu_secondary(void)
 	if (cpu_has_feature(CPU_FTR_ARCH_206)
 			&& cpu_has_feature(CPU_FTR_HVMODE))
 		tlbiel_all();
+
+#ifdef CONFIG_PPC_MEM_KEYS
+	mtspr(SPRN_UAMOR, default_uamor);
+#endif
 }
 #endif /* CONFIG_SMP */
 

arch/powerpc/mm/book3s64/pkeys.c

@@ -27,9 +27,7 @@ static u32 initial_allocation_mask __ro_after_init;
  */
 static u64 default_amr = ~0x0UL;
 static u64 default_iamr = 0x5555555555555555UL;
-
-/* Allow all keys to be modified by default */
-static u64 default_uamor = ~0x0UL;
+u64 default_uamor __ro_after_init;
 /*
  * Key used to implement PROT_EXEC mmap. Denies READ/WRITE
  * We pick key 2 because 0 is special key and 1 is reserved as per ISA.
@@ -122,10 +120,11 @@ void __init pkey_early_init_devtree(void)
 
 	/* scan the device tree for pkey feature */
 	pkeys_total = scan_pkey_feature();
-	if (!pkeys_total) {
-		/* No support for pkey. Mark it disabled */
-		return;
-	}
+	if (!pkeys_total)
+		goto out;
+
+	/* Allow all keys to be modified by default */
+	default_uamor = ~0x0UL;
 
 	cur_cpu_spec->mmu_features |= MMU_FTR_PKEY;
 
@@ -209,6 +208,12 @@ void __init pkey_early_init_devtree(void)
 	initial_allocation_mask |= reserved_allocation_mask;
 
 	pr_info("Enabling pkeys with max key count %d\n", num_pkey);
+out:
+	/*
+	 * Setup uamor on boot cpu
+	 */
+	mtspr(SPRN_UAMOR, default_uamor);
+
 	return;
 }
 
@@ -251,11 +256,6 @@ static inline u64 read_uamor(void)
 	return mfspr(SPRN_UAMOR);
 }
 
-static inline void write_uamor(u64 value)
-{
-	mtspr(SPRN_UAMOR, value);
-}
-
 static bool is_pkey_enabled(int pkey)
 {
 	u64 uamor = read_uamor();
@@ -326,7 +326,6 @@ void thread_pkey_regs_save(struct thread_struct *thread)
 	 */
 	thread->amr = read_amr();
 	thread->iamr = read_iamr();
-	thread->uamor = read_uamor();
 }
 
 void thread_pkey_regs_restore(struct thread_struct *new_thread,
@@ -339,8 +338,6 @@ void thread_pkey_regs_restore(struct thread_struct *new_thread,
 		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)
@@ -350,11 +347,9 @@ void thread_pkey_regs_init(struct thread_struct *thread)
 
 	thread->amr   = default_amr;
 	thread->iamr  = default_iamr;
-	thread->uamor = default_uamor;
 
 	write_amr(default_amr);
 	write_iamr(default_iamr);
-	write_uamor(default_uamor);
 }
 
 int execute_only_pkey(struct mm_struct *mm)

arch/powerpc/mm/book3s64/radix_pgtable.c

@@ -620,6 +620,10 @@ void setup_kuap(bool disabled)
 
 	/* Make sure userspace can't change the AMR */
 	mtspr(SPRN_UAMOR, 0);
+
+	/*
+	 * Set the default kernel AMR values on all cpus.
+	 */
 	mtspr(SPRN_AMR, AMR_KUAP_BLOCKED);
 	isync();
 }