powerpc/pkeys: Fix handling of pkey state across fork()

Protection key tracking information is not copied over to the
mm_struct of the child during fork(). 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.

Fixes: cf43d3b26452 ("powerpc: Enable pkey subsystem")
Cc: stable@vger.kernel.org # v4.16+
Reviewed-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index c05efd2e87369c11ae1f20033d386129f373f1b9..e687ed31d85ad465cb18b1a344265460168a3357 100644 (file)
--- 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;
-}
-
 #ifdef CONFIG_PPC_BOOK3E_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 04b60a8f6e6915d1ca29ea035700092a22f1df12..5878077637379fde5edb573fa3dad00f9eb043dc 100644 (file)
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -415,3 +415,13 @@ 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)
+{
+       if (static_branch_likely(&pkey_disabled))
+               return;
+
+       /* 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;
+}