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

Greg Kroah-Hartman
2019-04-15T19:15:46Z

From: Will Deacon <will.deacon@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: <stable@vger.kernel.org>
Fixes: 1149aad10b1e ("arm64: Add dump_backtrace() in show_regs")
Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@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
@@ -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;
}