[PATCH 18/18] powerpc/fault: Use analyse_instr() to check for store with updates to sp

[Jordan Niethe]

A user-mode access to an address a long way below the stack pointer is
only valid if the instruction is one that would update the stack pointer
to the address accessed. This is checked by directly looking at the
instructions op-code. As a result is does not take into account prefixed
instructions. Instead of looking at the instruction our self, use
analyse_instr() determine if this a store instruction that will update
the stack pointer.

Something to note is that there currently are not any store with update
prefixed instructions. Actually there is no plan for prefixed
update-form loads and stores. So this patch is probably not needed but
it might be preferable to use analyse_instr() rather than open coding
the test anyway.

Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
---
 arch/powerpc/mm/fault.c | 39 +++++++++++----------------------------
 1 file changed, 11 insertions(+), 28 deletions(-)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index b5047f9b5dec..cb78b3ca1800 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -41,37 +41,17 @@
 #include <asm/siginfo.h>
 #include <asm/debug.h>
 #include <asm/kup.h>
+#include <asm/sstep.h>
 
 /*
  * Check whether the instruction inst is a store using
  * an update addressing form which will update r1.
  */
-static bool store_updates_sp(unsigned int inst)
+static bool store_updates_sp(struct instruction_op *op)
 {
-	/* check for 1 in the rA field */
-	if (((inst >> 16) & 0x1f) != 1)
-		return false;
-	/* check major opcode */
-	switch (inst >> 26) {
-	case OP_STWU:
-	case OP_STBU:
-	case OP_STHU:
-	case OP_STFSU:
-	case OP_STFDU:
-		return true;
-	case OP_STD:	/* std or stdu */
-		return (inst & 3) == 1;
-	case OP_31:
-		/* check minor opcode */
-		switch ((inst >> 1) & 0x3ff) {
-		case OP_31_XOP_STDUX:
-		case OP_31_XOP_STWUX:
-		case OP_31_XOP_STBUX:
-		case OP_31_XOP_STHUX:
-		case OP_31_XOP_STFSUX:
-		case OP_31_XOP_STFDUX:
+	if (GETTYPE(op->type) == STORE) {
+		if ((op->type & UPDATE) && (op->update_reg == 1))
 			return true;
-		}
 	}
 	return false;
 }
@@ -278,14 +258,17 @@ static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
 
 		if ((flags & FAULT_FLAG_WRITE) && (flags & FAULT_FLAG_USER) &&
 		    access_ok(nip, sizeof(*nip))) {
-			unsigned int inst;
+			unsigned int inst, sufx;
+			struct instruction_op op;
 			int res;
 
 			pagefault_disable();
-			res = __get_user_inatomic(inst, nip);
+			res = __get_user_instr_inatomic(inst, sufx, nip);
 			pagefault_enable();
-			if (!res)
-				return !store_updates_sp(inst);
+			if (!res) {
+				analyse_instr(&op, uregs, inst, sufx);
+				return !store_updates_sp(&op);
+			}
 			*must_retry = true;
 		}
 		return true;
-- 
2.20.1