powerpc: introduce execute-only pkey

This patch provides the implementation of execute-only pkey.
The architecture-independent layer expects the arch-dependent
layer, to support the ability to create and enable a special
key which has execute-only permission.

Acked-by: Balbir Singh <bsingharora@gmail.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/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
index 37ef23c..0abeb0e 100644 (file)
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h
@@ -116,6 +116,7 @@ typedef struct {
         * bit unset -> key available for allocation
         */
        u32 pkey_allocation_map;
+       s16 execute_only_pkey; /* key holding execute-only protection */
 #endif
 } mm_context_t;
 

diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index 41c303a..b8d2a8e 100644 (file)
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h
@@ -117,9 +117,13 @@ static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
  * Try to dedicate one of the protection keys to be used as an
  * execute-only protection key.
  */
+extern int __execute_only_pkey(struct mm_struct *mm);
 static inline int execute_only_pkey(struct mm_struct *mm)
 {
-       return 0;
+       if (static_branch_likely(&pkey_disabled))
+               return -1;
+
+       return __execute_only_pkey(mm);
 }
 
 static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,

diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index 91ec6c4..6fece6e 100644 (file)
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -92,6 +92,8 @@ void pkey_mm_init(struct mm_struct *mm)
        if (static_branch_likely(&pkey_disabled))
                return;
        mm_pkey_allocation_map(mm) = initial_allocation_mask;
+       /* -1 means unallocated or invalid */
+       mm->context.execute_only_pkey = -1;
 }
 
 static inline u64 read_amr(void)
@@ -256,3 +258,59 @@ void thread_pkey_regs_init(struct thread_struct *thread)
        write_iamr(read_iamr() & pkey_iamr_mask);
        write_uamor(read_uamor() & pkey_amr_uamor_mask);
 }
+
+static inline bool pkey_allows_readwrite(int pkey)
+{
+       int pkey_shift = pkeyshift(pkey);
+
+       if (!is_pkey_enabled(pkey))
+               return true;
+
+       return !(read_amr() & ((AMR_RD_BIT|AMR_WR_BIT) << pkey_shift));
+}
+
+int __execute_only_pkey(struct mm_struct *mm)
+{
+       bool need_to_set_mm_pkey = false;
+       int execute_only_pkey = mm->context.execute_only_pkey;
+       int ret;
+
+       /* Do we need to assign a pkey for mm's execute-only maps? */
+       if (execute_only_pkey == -1) {
+               /* Go allocate one to use, which might fail */
+               execute_only_pkey = mm_pkey_alloc(mm);
+               if (execute_only_pkey < 0)
+                       return -1;
+               need_to_set_mm_pkey = true;
+       }
+
+       /*
+        * We do not want to go through the relatively costly dance to set AMR
+        * if we do not need to. Check it first and assume that if the
+        * execute-only pkey is readwrite-disabled than we do not have to set it
+        * ourselves.
+        */
+       if (!need_to_set_mm_pkey && !pkey_allows_readwrite(execute_only_pkey))
+               return execute_only_pkey;
+
+       /*
+        * Set up AMR so that it denies access for everything other than
+        * execution.
+        */
+       ret = __arch_set_user_pkey_access(current, execute_only_pkey,
+                                         PKEY_DISABLE_ACCESS |
+                                         PKEY_DISABLE_WRITE);
+       /*
+        * If the AMR-set operation failed somehow, just return 0 and
+        * effectively disable execute-only support.
+        */
+       if (ret) {
+               mm_pkey_free(mm, execute_only_pkey);
+               return -1;
+       }
+
+       /* We got one, store it and use it from here on out */
+       if (need_to_set_mm_pkey)
+               mm->context.execute_only_pkey = execute_only_pkey;
+       return execute_only_pkey;
+}