Subject: [PATCH] powerpc/pkeys: copy pkey-tracking-information at fork()

From: Ram Pai <[email-masked]>
Date: Mon, 3 Dec 2018 12:43:22 -0800

At fork(), the pkey tracking information is not copied over
to the mm_struct of the child. This can cause the child to erroneously
allocate keys that were already allocated. Any allocated execute-only
key is lost aswell.

Add code; called by dup_mmap(), to copy the pkey state from
parent to child explicitly.

This problem was originally found by Dave Hansen on x86, which turns
out to be a problem on powerpc aswell.

Testing:
	Passes the new selftest added by Dave Hansen. I have temporarily
	captured that selftest at
	https://github.com/rampai/memorykeys/ -b memkey.v15-rc6

Signed-off-by: Ram Pai <[email-masked]>
---
 arch/powerpc/include/asm/mmu_context.h |   15 +++++++++------
 arch/powerpc/mm/pkeys.c                |    7 +++++++
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 0381394..cb16146 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -217,12 +217,6 @@ static inline void enter_lazy_tlb(struct mm_struct *mm,
 #endif
 }
 
-static inline int arch_dup_mmap(struct mm_struct *oldmm,
-				struct mm_struct *mm)
-{
-	return 0;
-}
-
 #ifndef CONFIG_PPC_BOOK3S_64
 static inline void arch_exit_mmap(struct mm_struct *mm)
 {
@@ -247,6 +241,7 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
 #ifdef CONFIG_PPC_MEM_KEYS
 bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write,
 			       bool execute, bool foreign);
+void arch_dup_pkeys(struct mm_struct *oldmm, struct mm_struct *mm);
 #else /* CONFIG_PPC_MEM_KEYS */
 static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 		bool write, bool execute, bool foreign)
@@ -259,6 +254,7 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 #define thread_pkey_regs_save(thread)
 #define thread_pkey_regs_restore(new_thread, old_thread)
 #define thread_pkey_regs_init(thread)
+#define arch_dup_pkeys(oldmm, mm)
 
 static inline u64 pte_to_hpte_pkey_bits(u64 pteflags)
 {
@@ -267,5 +263,12 @@ static inline u64 pte_to_hpte_pkey_bits(u64 pteflags)
 
 #endif /* CONFIG_PPC_MEM_KEYS */
 
+static inline int arch_dup_mmap(struct mm_struct *oldmm,
+				struct mm_struct *mm)
+{
+	arch_dup_pkeys(oldmm, mm);
+	return 0;
+}
+
 #endif /* __KERNEL__ */
 #endif /* __ASM_POWERPC_MMU_CONTEXT_H */
diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index b271b28..5d65c47 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -414,3 +414,10 @@ bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write,
 
 	return pkey_access_permitted(vma_pkey(vma), write, execute);
 }
+
+void arch_dup_pkeys(struct mm_struct *oldmm, struct mm_struct *mm)
+{
+	/* Duplicate the oldmm pkey state in mm: */
+	mm_pkey_allocation_map(mm) = mm_pkey_allocation_map(oldmm);
+	mm->context.execute_only_pkey = oldmm->context.execute_only_pkey;
+}
-- 
1.7.1