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@xxxxxxxxx>
Signed-off-by: Ram Pai <linuxram@xxxxxxxxxx>
---
arch/powerpc/include/asm/book3s/64/mmu.h | 1 +
arch/powerpc/include/asm/pkeys.h | 8 ++++-
arch/powerpc/mm/pkeys.c | 56 ++++++++++++++++++++++++++++++
3 files changed, 64 insertions(+), 1 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
index df17fbc..44dbc91 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h
@@ -116,6 +116,7 @@ struct patb_entry {
* 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 0b2d9f0..20d1f0e 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h
@@ -128,9 +128,13 @@ 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,
@@ -154,6 +158,8 @@ static inline 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;
}
extern void thread_pkey_regs_save(struct thread_struct *thread);
diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index 469f370..5da94fe 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -247,3 +247,59 @@ 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;
+}
--
1.7.1
