ARM: Add an emulate flag to the kprobes/uprobes instruction decode functions

Add an emulate flag into the instruction interpreter, primarily for uprobes
support.

Signed-off-by: David A. Long <dave.long@linaro.org>
Acked-by: Jon Medhurst <tixy@linaro.org>

arch/arm/kernel/kprobes.c

@@ -89,7 +89,7 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 	p->opcode = insn;
 	p->ainsn.insn = tmp_insn;
 
-	switch ((*decode_insn)(insn, &p->ainsn, actions)) {
+	switch ((*decode_insn)(insn, &p->ainsn, true, actions)) {
 	case INSN_REJECTED:	/* not supported */
 		return -EINVAL;
 

arch/arm/kernel/kprobes.h

@@ -35,6 +35,7 @@ kprobe_decode_ldmstm(kprobe_opcode_t insn, struct arch_specific_insn *asi,
 
 typedef enum probes_insn (kprobe_decode_insn_t)(probes_opcode_t,
 						struct arch_specific_insn *,
+						bool,
 						const union decode_action *);
 
 #ifdef CONFIG_THUMB2_KERNEL

arch/arm/kernel/probes-arm.c

@@ -725,10 +725,10 @@ static void __kprobes arm_singlestep(probes_opcode_t insn,
  */
 enum probes_insn __kprobes
 arm_probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
-		       const union decode_action *actions)
+		       bool emulate, const union decode_action *actions)
 {
 	asi->insn_singlestep = arm_singlestep;
 	asi->insn_check_cc = probes_condition_checks[insn>>28];
 	return probes_decode_insn(insn, asi, probes_decode_arm_table, false,
-				  actions);
+				  emulate, actions);
 }

arch/arm/kernel/probes-arm.h

@@ -67,7 +67,7 @@ void __kprobes simulate_mov_ipsp(probes_opcode_t opcode,
 extern const union decode_item probes_decode_arm_table[];
 
 enum probes_insn arm_probes_decode_insn(probes_opcode_t,
-		struct arch_specific_insn *,
+		struct arch_specific_insn *, bool emulate,
 		const union decode_action *actions);
 
 #endif

arch/arm/kernel/probes-thumb.c

@@ -863,20 +863,20 @@ static void __kprobes thumb32_singlestep(probes_opcode_t opcode,
 
 enum probes_insn __kprobes
 thumb16_probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
-			   const union decode_action *actions)
+			   bool emulate, const union decode_action *actions)
 {
 	asi->insn_singlestep = thumb16_singlestep;
 	asi->insn_check_cc = thumb_check_cc;
 	return probes_decode_insn(insn, asi, probes_decode_thumb16_table, true,
-				  actions);
+				  emulate, actions);
 }
 
 enum probes_insn __kprobes
 thumb32_probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
-			   const union decode_action *actions)
+			   bool emulate, const union decode_action *actions)
 {
 	asi->insn_singlestep = thumb32_singlestep;
 	asi->insn_check_cc = thumb_check_cc;
 	return probes_decode_insn(insn, asi, probes_decode_thumb32_table, true,
-				  actions);
+				  emulate, actions);
 }

arch/arm/kernel/probes-thumb.h

@@ -89,9 +89,9 @@ extern const union decode_item probes_decode_thumb16_table[];
 
 enum probes_insn __kprobes
 thumb16_probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
-		const union decode_action *actions);
+		bool emulate, const union decode_action *actions);
 enum probes_insn __kprobes
 thumb32_probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
-		const union decode_action *actions);
+		bool emulate, const union decode_action *actions);
 
 #endif

arch/arm/kernel/probes.c

@@ -257,7 +257,7 @@ set_emulated_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
  * non-zero value, the corresponding nibble in pinsn is validated and modified
  * according to the type.
  */
-static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs)
+static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs, bool modify)
 {
 	probes_opcode_t insn = *pinsn;
 	probes_opcode_t mask = 0xf; /* Start at least significant nibble */
@@ -323,7 +323,9 @@ static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs)
 		insn |= new_bits & mask;
 	}
 
-	*pinsn = insn;
+	if (modify)
+		*pinsn = insn;
+
 	return true;
 
 reject:
@@ -385,13 +387,14 @@ static const int decode_struct_sizes[NUM_DECODE_TYPES] = {
 int __kprobes
 probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
 		   const union decode_item *table, bool thumb,
-		   const union decode_action *actions)
+		   bool emulate, const union decode_action *actions)
 {
 	const struct decode_header *h = (struct decode_header *)table;
 	const struct decode_header *next;
 	bool matched = false;
 
-	insn = prepare_emulated_insn(insn, asi, thumb);
+	if (emulate)
+		insn = prepare_emulated_insn(insn, asi, thumb);
 
 	for (;; h = next) {
 		enum decode_type type = h->type_regs.bits & DECODE_TYPE_MASK;
@@ -406,7 +409,7 @@ probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
 		if (!matched && (insn & h->mask.bits) != h->value.bits)
 			continue;
 
-		if (!decode_regs(&insn, regs))
+		if (!decode_regs(&insn, regs, emulate))
 			return INSN_REJECTED;
 
 		switch (type) {
@@ -430,6 +433,11 @@ probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
 
 		case DECODE_TYPE_EMULATE: {
 			struct decode_emulate *d = (struct decode_emulate *)h;
+
+			if (!emulate)
+				return actions[d->handler.action].decoder(insn,
+					asi, h);
+
 			asi->insn_handler = actions[d->handler.action].handler;
 			set_emulated_insn(insn, asi, thumb);
 			return INSN_GOOD;

arch/arm/kernel/probes.h

@@ -401,7 +401,7 @@ probes_insn_handler_t probes_emulate_none;
 
 int __kprobes
 probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
-		const union decode_item *table, bool thumb,
+		const union decode_item *table, bool thumb, bool emulate,
 		const union decode_action *actions);
 
 #endif