[PATCH 5.0 094/117] arm64: backtrace: Dont bother trying to unwind the userspace stack

[Greg Kroah-Hartman]

From: Will Deacon <will.deacon@xxxxxxx>

commit 1e6f5440a6814d28c32d347f338bfef68bc3e69d upstream.

Calling dump_backtrace() with a pt_regs argument corresponding to
userspace doesn't make any sense and our unwinder will simply print
"Call trace:" before unwinding the stack looking for user frames.

Rather than go through this song and dance, just return early if we're
passed a user register state.

Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: 1149aad10b1e ("arm64: Add dump_backtrace() in show_regs")
Reported-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/arm64/kernel/traps.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -102,10 +102,16 @@ static void dump_instr(const char *lvl,
 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 {
 	struct stackframe frame;
-	int skip;
+	int skip = 0;
 
 	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 
+	if (regs) {
+		if (user_mode(regs))
+			return;
+		skip = 1;
+	}
+
 	if (!tsk)
 		tsk = current;
 
@@ -126,7 +132,6 @@ void dump_backtrace(struct pt_regs *regs
 	frame.graph = 0;
 #endif
 
-	skip = !!regs;
 	printk("Call trace:\n");
 	do {
 		/* skip until specified stack frame */
@@ -176,15 +181,13 @@ static int __die(const char *str, int er
 		return ret;
 
 	print_modules();
-	__show_regs(regs);
 	pr_emerg("Process %.*s (pid: %d, stack limit = 0x%p)\n",
 		 TASK_COMM_LEN, tsk->comm, task_pid_nr(tsk),
 		 end_of_stack(tsk));
+	show_regs(regs);
 
-	if (!user_mode(regs)) {
-		dump_backtrace(regs, tsk);
+	if (!user_mode(regs))
 		dump_instr(KERN_EMERG, regs);
-	}
 
 	return ret;
 }