powerpc: split validate_sp into two functions

Most callers just want to validate an arbitrary kernel stack pointer,
some need a particular size. Make the size case the exceptional one
with an extra function.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221127124942.1665522-15-npiggin@gmail.com

arch/powerpc/include/asm/processor.h

@@ -374,9 +374,18 @@ static inline unsigned long __pack_fe01(unsigned int fpmode)
 
 #endif
 
-/* Check that a certain kernel stack pointer is valid in task_struct p */
-int validate_sp(unsigned long sp, struct task_struct *p,
-                       unsigned long nbytes);
+/*
+ * Check that a certain kernel stack pointer is a valid (minimum sized)
+ * stack frame in task_struct p.
+ */
+int validate_sp(unsigned long sp, struct task_struct *p);
+
+/*
+ * validate the stack frame of a particular minimum size, used for when we are
+ * looking at a certain object in the stack beyond the minimum.
+ */
+int validate_sp_size(unsigned long sp, struct task_struct *p,
+		     unsigned long nbytes);
 
 /*
  * Prefetch macros.

arch/powerpc/kernel/process.c

@@ -2157,9 +2157,12 @@ static inline int valid_emergency_stack(unsigned long sp, struct task_struct *p,
 	return 0;
 }
 
-
-int validate_sp(unsigned long sp, struct task_struct *p,
-		       unsigned long nbytes)
+/*
+ * validate the stack frame of a particular minimum size, used for when we are
+ * looking at a certain object in the stack beyond the minimum.
+ */
+int validate_sp_size(unsigned long sp, struct task_struct *p,
+		     unsigned long nbytes)
 {
 	unsigned long stack_page = (unsigned long)task_stack_page(p);
 
@@ -2175,21 +2178,23 @@ int validate_sp(unsigned long sp, struct task_struct *p,
 	return valid_emergency_stack(sp, p, nbytes);
 }
 
-EXPORT_SYMBOL(validate_sp);
+int validate_sp(unsigned long sp, struct task_struct *p)
+{
+	return validate_sp_size(sp, p, STACK_FRAME_OVERHEAD);
+}
 
 static unsigned long ___get_wchan(struct task_struct *p)
 {
 	unsigned long ip, sp;
 	int count = 0;
 
 	sp = p->thread.ksp;
-	if (!validate_sp(sp, p, STACK_FRAME_OVERHEAD))
+	if (!validate_sp(sp, p))
 		return 0;
 
 	do {
 		sp = READ_ONCE_NOCHECK(*(unsigned long *)sp);
-		if (!validate_sp(sp, p, STACK_FRAME_OVERHEAD) ||
-		    task_is_running(p))
+		if (!validate_sp(sp, p) || task_is_running(p))
 			return 0;
 		if (count > 0) {
 			ip = READ_ONCE_NOCHECK(((unsigned long *)sp)[STACK_FRAME_LR_SAVE]);
@@ -2243,7 +2248,7 @@ void __no_sanitize_address show_stack(struct task_struct *tsk,
 	lr = 0;
 	printk("%sCall Trace:\n", loglvl);
 	do {
-		if (!validate_sp(sp, tsk, STACK_FRAME_OVERHEAD))
+		if (!validate_sp(sp, tsk))
 			break;
 
 		stack = (unsigned long *) sp;
@@ -2270,7 +2275,7 @@ void __no_sanitize_address show_stack(struct task_struct *tsk,
 		 * could hold a pt_regs, if that does not fit then it can't
 		 * have regs.
 		 */
-		if (validate_sp(sp, tsk, STACK_SWITCH_FRAME_SIZE)
+		if (validate_sp_size(sp, tsk, STACK_SWITCH_FRAME_SIZE)
 		    && stack[STACK_INT_FRAME_MARKER_LONGS] == STACK_FRAME_REGS_MARKER) {
 			struct pt_regs *regs = (struct pt_regs *)
 				(sp + STACK_INT_FRAME_REGS);

arch/powerpc/kernel/stacktrace.c

@@ -43,7 +43,7 @@ void __no_sanitize_address arch_stack_walk(stack_trace_consume_fn consume_entry,
 		unsigned long *stack = (unsigned long *) sp;
 		unsigned long newsp, ip;
 
-		if (!validate_sp(sp, task, STACK_FRAME_OVERHEAD))
+		if (!validate_sp(sp, task))
 			return;
 
 		newsp = stack[0];

arch/powerpc/perf/callchain.c

@@ -27,7 +27,7 @@ static int valid_next_sp(unsigned long sp, unsigned long prev_sp)
 {
 	if (sp & 0xf)
 		return 0;		/* must be 16-byte aligned */
-	if (!validate_sp(sp, current, STACK_FRAME_OVERHEAD))
+	if (!validate_sp(sp, current))
 		return 0;
 	if (sp >= prev_sp + STACK_FRAME_MIN_SIZE)
 		return 1;
@@ -53,15 +53,15 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
 	sp = regs->gpr[1];
 	perf_callchain_store(entry, perf_instruction_pointer(regs));
 
-	if (!validate_sp(sp, current, STACK_FRAME_OVERHEAD))
+	if (!validate_sp(sp, current))
 		return;
 
 	for (;;) {
 		fp = (unsigned long *) sp;
 		next_sp = fp[0];
 
 		if (next_sp == sp + STACK_INT_FRAME_SIZE &&
-		    validate_sp(sp, current, STACK_INT_FRAME_SIZE) &&
+		    validate_sp_size(sp, current, STACK_INT_FRAME_SIZE) &&
 		    fp[STACK_INT_FRAME_MARKER_LONGS] == STACK_FRAME_REGS_MARKER) {
 			/*
 			 * This looks like an interrupt frame for an