Re: [PATCH 11/25] powerpc: introduce execute-only pkey

On Thu, Oct 19, 2017 at 10:02:13AM +1100, Balbir Singh wrote:

On Wed, 18 Oct 2017 13:57:39 -0700
Ram Pai [off-list ref] wrote:

quoted

On Wed, Oct 18, 2017 at 03:15:22PM +1100, Balbir Singh wrote:

quoted

On Fri,  8 Sep 2017 15:44:59 -0700
Ram Pai [off-list ref] wrote:
  

quoted

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.

Signed-off-by: Ram Pai <redacted>
---
 arch/powerpc/include/asm/book3s/64/mmu.h |    1 +
 arch/powerpc/include/asm/pkeys.h         |    9 ++++-
 arch/powerpc/mm/pkeys.c                  |   57 ++++++++++++++++++++++++++++++
 3 files changed, 66 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
index 55950f4..ee18ba0 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h

@@ -115,6 +115,7 @@ 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 78c5362..0cf115f 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h

@@ -115,11 +115,16 @@ 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 (!pkey_inited || !pkey_execute_disable_support)
+		return -1;
+
+	return __execute_only_pkey(mm);
 }
 
+
 static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,
 		int prot, int pkey)
 {

@@ -141,6 +146,8 @@ static inline void pkey_mm_init(struct mm_struct *mm)
 	if (!pkey_inited)
 		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 7cd1be4..8a24983 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c

@@ -188,3 +188,60 @@ void thread_pkey_regs_init(struct thread_struct *thread)
 	write_iamr(0x0ul);
 	write_uamor(0x0ul);
 }
+
+static inline bool pkey_allows_readwrite(int pkey)
+{
+	int pkey_shift = pkeyshift(pkey);
+
+	if (!(read_uamor() & (0x3UL << pkey_shift)))
+		return true;  

If uamor for key 0 is 0x10 for example or 0x01 it's a bug.
The above check might miss it.  

The specs says both the bits corresponding to a key are set or
reset, cannot be anything else.

I agree, thats why I said it's a bug if the values are such.
Do we care to validate that both bits are the same?

I will put in a assert. Will that work?

RP

Balbir Singh.

-- 
Ram Pai