[PATCH 4.14 59/69] arm64: backtrace: Dont bother trying to unwind the userspace stack

[Greg Kroah-Hartman]

From: Will Deacon <will.dea...@arm.com>

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: <sta...@vger.kernel.org>
Fixes: 1149aad10b1e ("arm64: Add dump_backtrace() in show_regs")
Reported-by: Kefeng Wang <wangkefeng.w...@huawei.com>
Signed-off-by: Will Deacon <will.dea...@arm.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 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
@@ -145,10 +145,16 @@ 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;
 
@@ -169,7 +175,6 @@ void dump_backtrace(struct pt_regs *regs
        frame.graph = tsk->curr_ret_stack;
 #endif
 
-       skip = !!regs;
        printk("Call trace:\n");
        while (1) {
                unsigned long stack;
@@ -232,15 +237,13 @@ 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;
 }