Subject: [PATCH v5 22/23] powerpc/book3s64/hash/kup: Don't hardcode kup key

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 27 Aug 2020 09:39:30 +0530

Make KUAP/KUEP key a variable and also check whether the platform
limit the max key such that we can't use the key for KUAP/KEUP.

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 .../powerpc/include/asm/book3s/64/hash-pkey.h | 22 +-------
 arch/powerpc/include/asm/book3s/64/pkeys.h    |  1 +
 arch/powerpc/mm/book3s64/pkeys.c              | 53 ++++++++++++++++---
 3 files changed, 49 insertions(+), 27 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/hash-pkey.h b/arch/powerpc/include/asm/book3s/64/hash-pkey.h
index 9f44e208f036..ff9907c72ee3 100644
--- a/arch/powerpc/include/asm/book3s/64/hash-pkey.h
+++ b/arch/powerpc/include/asm/book3s/64/hash-pkey.h
@@ -2,9 +2,7 @@
 #ifndef _ASM_POWERPC_BOOK3S_64_HASH_PKEY_H
 #define _ASM_POWERPC_BOOK3S_64_HASH_PKEY_H
 
-/*  We use key 3 for KERNEL */
-#define HASH_DEFAULT_KERNEL_KEY (HPTE_R_KEY_BIT0 | HPTE_R_KEY_BIT1)
-
+u64 pte_to_hpte_pkey_bits(u64 pteflags, unsigned long flags);
 static inline u64 hash__vmflag_to_pte_pkey_bits(u64 vm_flags)
 {
 	return (((vm_flags & VM_PKEY_BIT0) ? H_PTE_PKEY_BIT0 : 0x0UL) |
@@ -14,24 +12,6 @@ static inline u64 hash__vmflag_to_pte_pkey_bits(u64 vm_flags)
 		((vm_flags & VM_PKEY_BIT4) ? H_PTE_PKEY_BIT4 : 0x0UL));
 }
 
-static inline u64 pte_to_hpte_pkey_bits(u64 pteflags, unsigned long flags)
-{
-	unsigned long pte_pkey;
-
-	pte_pkey = (((pteflags & H_PTE_PKEY_BIT4) ? HPTE_R_KEY_BIT4 : 0x0UL) |
-		    ((pteflags & H_PTE_PKEY_BIT3) ? HPTE_R_KEY_BIT3 : 0x0UL) |
-		    ((pteflags & H_PTE_PKEY_BIT2) ? HPTE_R_KEY_BIT2 : 0x0UL) |
-		    ((pteflags & H_PTE_PKEY_BIT1) ? HPTE_R_KEY_BIT1 : 0x0UL) |
-		    ((pteflags & H_PTE_PKEY_BIT0) ? HPTE_R_KEY_BIT0 : 0x0UL));
-
-	if (mmu_has_feature(MMU_FTR_KUAP) || mmu_has_feature(MMU_FTR_KUEP)) {
-		if ((pte_pkey == 0) && (flags & HPTE_USE_KERNEL_KEY))
-			return HASH_DEFAULT_KERNEL_KEY;
-	}
-
-	return pte_pkey;
-}
-
 static inline u16 hash__pte_to_pkey_bits(u64 pteflags)
 {
 	return (((pteflags & H_PTE_PKEY_BIT4) ? 0x10 : 0x0UL) |
diff --git a/arch/powerpc/include/asm/book3s/64/pkeys.h b/arch/powerpc/include/asm/book3s/64/pkeys.h
index 3b8640498f5b..a2b6c4a7275f 100644
--- a/arch/powerpc/include/asm/book3s/64/pkeys.h
+++ b/arch/powerpc/include/asm/book3s/64/pkeys.h
@@ -8,6 +8,7 @@
 extern u64 __ro_after_init default_uamor;
 extern u64 __ro_after_init default_amr;
 extern u64 __ro_after_init default_iamr;
+extern int kup_key;
 
 static inline u64 vmflag_to_pte_pkey_bits(u64 vm_flags)
 {
diff --git a/arch/powerpc/mm/book3s64/pkeys.c b/arch/powerpc/mm/book3s64/pkeys.c
index b862d5cd78ff..cb1d7d39e801 100644
--- a/arch/powerpc/mm/book3s64/pkeys.c
+++ b/arch/powerpc/mm/book3s64/pkeys.c
@@ -37,7 +37,10 @@ u64 default_uamor __ro_after_init;
  */
 static int execute_only_key = 2;
 static bool pkey_execute_disable_supported;
-
+/*
+ * key used to implement KUAP/KUEP with hash translation.
+ */
+int kup_key = 3;
 
 #define AMR_BITS_PER_PKEY 2
 #define AMR_RD_BIT 0x1UL
@@ -185,6 +188,25 @@ void __init pkey_early_init_devtree(void)
 		default_uamor &= ~(0x3ul << pkeyshift(execute_only_key));
 	}
 
+	if (unlikely(num_pkey <= kup_key)) {
+		/*
+		 * Insufficient number of keys to support
+		 * KUAP/KUEP feature.
+		 */
+		kup_key = -1;
+	} else {
+		/*  handle key which is used by kernel for KAUP */
+		reserved_allocation_mask |= (0x1 << kup_key);
+		/*
+		 * Mark access for kup_key in default amr so that
+		 * we continue to operate with that AMR in
+		 * copy_to/from_user().
+		 */
+		default_amr   &= ~(0x3ul << pkeyshift(kup_key));
+		default_iamr  &= ~(0x1ul << pkeyshift(kup_key));
+		default_uamor &= ~(0x3ul << pkeyshift(kup_key));
+	}
+
 	/*
 	 * Allow access for only key 0. And prevent any other modification.
 	 */
@@ -205,9 +227,6 @@ void __init pkey_early_init_devtree(void)
 	reserved_allocation_mask |= (0x1 << 1);
 	default_uamor &= ~(0x3ul << pkeyshift(1));
 
-	/*  handle key 3 which is used by kernel for KAUP */
-	reserved_allocation_mask |= (0x1 << 3);
-	default_uamor &= ~(0x3ul << pkeyshift(3));
 
 	/*
 	 * Prevent the usage of OS reserved keys. Update UAMOR
@@ -236,7 +255,7 @@ void __init pkey_early_init_devtree(void)
 #ifdef CONFIG_PPC_KUEP
 void __init setup_kuep(bool disabled)
 {
-	if (disabled)
+	if (disabled || kup_key == -1)
 		return;
 	/*
 	 * On hash if PKEY feature is not enabled, disable KUAP too.
@@ -262,7 +281,7 @@ void __init setup_kuep(bool disabled)
 #ifdef CONFIG_PPC_KUAP
 void __init setup_kuap(bool disabled)
 {
-	if (disabled)
+	if (disabled || kup_key == -1)
 		return;
 	/*
 	 * On hash if PKEY feature is not enabled, disable KUAP too.
@@ -458,4 +477,26 @@ void arch_dup_pkeys(struct mm_struct *oldmm, struct mm_struct *mm)
 	mm->context.execute_only_pkey = oldmm->context.execute_only_pkey;
 }
 
+u64 pte_to_hpte_pkey_bits(u64 pteflags, unsigned long flags)
+{
+	unsigned long pte_pkey;
+
+	pte_pkey = (((pteflags & H_PTE_PKEY_BIT4) ? HPTE_R_KEY_BIT4 : 0x0UL) |
+		    ((pteflags & H_PTE_PKEY_BIT3) ? HPTE_R_KEY_BIT3 : 0x0UL) |
+		    ((pteflags & H_PTE_PKEY_BIT2) ? HPTE_R_KEY_BIT2 : 0x0UL) |
+		    ((pteflags & H_PTE_PKEY_BIT1) ? HPTE_R_KEY_BIT1 : 0x0UL) |
+		    ((pteflags & H_PTE_PKEY_BIT0) ? HPTE_R_KEY_BIT0 : 0x0UL));
+
+	if (mmu_has_feature(MMU_FTR_KUAP) || mmu_has_feature(MMU_FTR_KUEP)) {
+		if ((pte_pkey == 0) &&
+		    (flags & HPTE_USE_KERNEL_KEY) && (kup_key != -1)) {
+			u64 vm_flag = pkey_to_vmflag_bits(kup_key);
+			u64 pte_flag = hash__vmflag_to_pte_pkey_bits(vm_flag);
+			return pte_to_hpte_pkey_bits(pte_flag, 0);
+		}
+	}
+
+	return pte_pkey;
+}
+
 #endif /* CONFIG_PPC_MEM_KEYS */
-- 
2.26.2