Subject: [PATCH 13/25] powerpc: implementation for arch_override_mprotect_pkey()

From: Ram Pai <[email-masked]>
Date: Fri, 8 Sep 2017 15:45:01 -0700

arch independent code calls arch_override_mprotect_pkey()
to return a pkey that best matches the requested protection.

This patch provides the implementation.

Signed-off-by: Ram Pai <[email-masked]>
---
 arch/powerpc/include/asm/mmu_context.h |    5 +++
 arch/powerpc/include/asm/pkeys.h       |   17 ++++++++++-
 arch/powerpc/mm/pkeys.c                |   47 ++++++++++++++++++++++++++++++++
 3 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index c705a5d..8e5a87e 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -145,6 +145,11 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 #ifndef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
 #define pkey_initialize()
 #define pkey_mm_init(mm)
+
+static inline int vma_pkey(struct vm_area_struct *vma)
+{
+	return 0;
+}
 #endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
 
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index f13e913..d2fffef 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h
@@ -41,6 +41,16 @@ static inline u64 pkey_to_vmflag_bits(u16 pkey)
 		((pkey & 0x10UL) ? VM_PKEY_BIT4 : 0x0UL));
 }
 
+#define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | \
+				VM_PKEY_BIT3 | VM_PKEY_BIT4)
+
+static inline int vma_pkey(struct vm_area_struct *vma)
+{
+	if (!pkey_inited)
+		return 0;
+	return (vma->vm_flags & ARCH_VM_PKEY_FLAGS) >> VM_PKEY_SHIFT;
+}
+
 #define arch_max_pkey()  pkeys_total
 #define AMR_RD_BIT 0x1UL
 #define AMR_WR_BIT 0x2UL
@@ -142,11 +152,14 @@ static inline int execute_only_pkey(struct mm_struct *mm)
 	return __execute_only_pkey(mm);
 }
 
-
+extern int __arch_override_mprotect_pkey(struct vm_area_struct *vma,
+		int prot, int pkey);
 static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,
 		int prot, int pkey)
 {
-	return 0;
+	if (!pkey_inited)
+		return 0;
+	return __arch_override_mprotect_pkey(vma, prot, pkey);
 }
 
 extern int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index 8a24983..fb1a76a 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -245,3 +245,50 @@ int __execute_only_pkey(struct mm_struct *mm)
 		mm->context.execute_only_pkey = execute_only_pkey;
 	return execute_only_pkey;
 }
+
+static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
+{
+	/* Do this check first since the vm_flags should be hot */
+	if ((vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) != VM_EXEC)
+		return false;
+
+	return (vma_pkey(vma) == vma->vm_mm->context.execute_only_pkey);
+}
+
+/*
+ * This should only be called for *plain* mprotect calls.
+ */
+int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
+		int pkey)
+{
+	/*
+	 * Is this an mprotect_pkey() call?  If so, never
+	 * override the value that came from the user.
+	 */
+	if (pkey != -1)
+		return pkey;
+
+	/*
+	 * If the currently associated pkey is execute-only,
+	 * but the requested protection requires read or write,
+	 * move it back to the default pkey.
+	 */
+	if (vma_is_pkey_exec_only(vma) &&
+	    (prot & (PROT_READ|PROT_WRITE)))
+		return 0;
+
+	/*
+	 * the requested protection is execute-only. Hence
+	 * lets use a execute-only pkey.
+	 */
+	if (prot == PROT_EXEC) {
+		pkey = execute_only_pkey(vma->vm_mm);
+		if (pkey > 0)
+			return pkey;
+	}
+
+	/*
+	 * nothing to override.
+	 */
+	return vma_pkey(vma);
+}
-- 
1.7.1