powerpc: Handle exceptions caused by pkey violation

Handle Data and  Instruction exceptions caused by memory
protection-key.

The CPU will detect the key fault if the HPTE is already
programmed with the key.

However if the HPTE is not  hashed, a key fault will not
be detected by the hardware. The software will detect
pkey violation in such a case.

Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/reg.h

@@ -312,7 +312,6 @@
 				 DSISR_BAD_EXT_CTRL)
 #define	  DSISR_BAD_FAULT_64S	(DSISR_BAD_FAULT_32S	| \
 				 DSISR_ATTR_CONFLICT	| \
-				 DSISR_KEYFAULT		| \
 				 DSISR_UNSUPP_MMU	| \
 				 DSISR_PRTABLE_FAULT	| \
 				 DSISR_ICSWX_NO_CT	| \

arch/powerpc/kernel/exceptions-64s.S

@@ -1527,7 +1527,7 @@ USE_TEXT_SECTION()
 	.balign	IFETCH_ALIGN_BYTES
 do_hash_page:
 #ifdef CONFIG_PPC_BOOK3S_64
-	lis	r0,(DSISR_BAD_FAULT_64S|DSISR_DABRMATCH)@h
+	lis	r0,(DSISR_BAD_FAULT_64S | DSISR_DABRMATCH | DSISR_KEYFAULT)@h
 	ori	r0,r0,DSISR_BAD_FAULT_64S@l
 	and.	r0,r4,r0		/* weird error? */
 	bne-	handle_page_fault	/* if not, try to insert a HPTE */

arch/powerpc/mm/fault.c

@@ -427,6 +427,11 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
 
+	if (error_code & DSISR_KEYFAULT) {
+		_exception(SIGSEGV, regs, SEGV_PKUERR, address);
+		return 0;
+	}
+
 	/*
 	 * We want to do this outside mmap_sem, because reading code around nip
 	 * can result in fault, which will cause a deadlock when called with
@@ -498,6 +503,23 @@ good_area:
 	 * the fault.
 	 */
 	fault = handle_mm_fault(vma, address, flags);
+
+#ifdef CONFIG_PPC_MEM_KEYS
+	/*
+	 * if the HPTE is not hashed, hardware will not detect
+	 * a key fault. Lets check if we failed because of a
+	 * software detected key fault.
+	 */
+	if (unlikely(fault & VM_FAULT_SIGSEGV) &&
+		!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
+			is_exec, 0)) {
+		int pkey = vma_pkey(vma);
+
+		if (likely(pkey))
+			return __bad_area(regs, address, SEGV_PKUERR);
+	}
+#endif /* CONFIG_PPC_MEM_KEYS */
+
 	major |= fault & VM_FAULT_MAJOR;
 
 	/*