powerpc: Add a probe_kernel_read_inst() function

Introduce a probe_kernel_read_inst() function to use in cases where
probe_kernel_read() is used for getting an instruction. This will be
more useful for prefixed instructions.
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Reviewed-by: Alistair Popple <alistair@popple.id.au>
[mpe: Don't write to *inst on error]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200506034050.24806-15-jniethe5@gmail.com

arch/powerpc/include/asm/inst.h

@@ -40,4 +40,7 @@ static inline bool ppc_inst_equal(struct ppc_inst x, struct ppc_inst y)
 int probe_user_read_inst(struct ppc_inst *inst,
 			 struct ppc_inst __user *nip);
 
+int probe_kernel_read_inst(struct ppc_inst *inst,
+			   struct ppc_inst *src);
+
 #endif /* _ASM_POWERPC_INST_H */

arch/powerpc/kernel/trace/ftrace.c

@@ -68,7 +68,7 @@ ftrace_modify_code(unsigned long ip, struct ppc_inst old, struct ppc_inst new)
 	 */
 
 	/* read the text we want to modify */
-	if (probe_kernel_read(&replaced, (void *)ip, MCOUNT_INSN_SIZE))
+	if (probe_kernel_read_inst(&replaced, (void *)ip))
 		return -EFAULT;
 
 	/* Make sure it is what we expect it to be */
@@ -130,7 +130,7 @@ __ftrace_make_nop(struct module *mod,
 	struct ppc_inst op, pop;
 
 	/* read where this goes */
-	if (probe_kernel_read(&op, (void *)ip, sizeof(int))) {
+	if (probe_kernel_read_inst(&op, (void *)ip)) {
 		pr_err("Fetching opcode failed.\n");
 		return -EFAULT;
 	}
@@ -164,7 +164,7 @@ __ftrace_make_nop(struct module *mod,
 	/* When using -mkernel_profile there is no load to jump over */
 	pop = ppc_inst(PPC_INST_NOP);
 
-	if (probe_kernel_read(&op, (void *)(ip - 4), 4)) {
+	if (probe_kernel_read_inst(&op, (void *)(ip - 4))) {
 		pr_err("Fetching instruction at %lx failed.\n", ip - 4);
 		return -EFAULT;
 	}
@@ -197,7 +197,7 @@ __ftrace_make_nop(struct module *mod,
 	 * Check what is in the next instruction. We can see ld r2,40(r1), but
 	 * on first pass after boot we will see mflr r0.
 	 */
-	if (probe_kernel_read(&op, (void *)(ip+4), MCOUNT_INSN_SIZE)) {
+	if (probe_kernel_read_inst(&op, (void *)(ip + 4))) {
 		pr_err("Fetching op failed.\n");
 		return -EFAULT;
 	}
@@ -349,7 +349,7 @@ static int setup_mcount_compiler_tramp(unsigned long tramp)
 			return -1;
 
 	/* New trampoline -- read where this goes */
-	if (probe_kernel_read(&op, (void *)tramp, sizeof(int))) {
+	if (probe_kernel_read_inst(&op, (void *)tramp)) {
 		pr_debug("Fetching opcode failed.\n");
 		return -1;
 	}
@@ -399,7 +399,7 @@ static int __ftrace_make_nop_kernel(struct dyn_ftrace *rec, unsigned long addr)
 	struct ppc_inst op;
 
 	/* Read where this goes */
-	if (probe_kernel_read(&op, (void *)ip, sizeof(int))) {
+	if (probe_kernel_read_inst(&op, (void *)ip)) {
 		pr_err("Fetching opcode failed.\n");
 		return -EFAULT;
 	}
@@ -526,7 +526,10 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	struct module *mod = rec->arch.mod;
 
 	/* read where this goes */
-	if (probe_kernel_read(op, ip, sizeof(op)))
+	if (probe_kernel_read_inst(op, ip))
+		return -EFAULT;
+
+	if (probe_kernel_read_inst(op + 1, ip + 4))
 		return -EFAULT;
 
 	if (!expected_nop_sequence(ip, op[0], op[1])) {
@@ -589,7 +592,7 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	unsigned long ip = rec->ip;
 
 	/* read where this goes */
-	if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE))
+	if (probe_kernel_read_inst(&op, (void *)ip))
 		return -EFAULT;
 
 	/* It should be pointing to a nop */
@@ -645,7 +648,7 @@ static int __ftrace_make_call_kernel(struct dyn_ftrace *rec, unsigned long addr)
 	}
 
 	/* Make sure we have a nop */
-	if (probe_kernel_read(&op, ip, sizeof(op))) {
+	if (probe_kernel_read_inst(&op, ip)) {
 		pr_err("Unable to read ftrace location %p\n", ip);
 		return -EFAULT;
 	}
@@ -723,7 +726,7 @@ __ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 	}
 
 	/* read where this goes */
-	if (probe_kernel_read(&op, (void *)ip, sizeof(int))) {
+	if (probe_kernel_read_inst(&op, (void *)ip)) {
 		pr_err("Fetching opcode failed.\n");
 		return -EFAULT;
 	}

arch/powerpc/lib/inst.c

@@ -18,3 +18,16 @@ int probe_user_read_inst(struct ppc_inst *inst,
 
 	return err;
 }
+
+int probe_kernel_read_inst(struct ppc_inst *inst,
+			   struct ppc_inst *src)
+{
+	unsigned int val;
+	int err;
+
+	err = probe_kernel_read(&val, src, sizeof(val));
+	if (!err)
+		*inst = ppc_inst(val);
+
+	return err;
+}