Put the boundary check before it accesses user space to prevent unnecessary
access which might crash the machine.
Especially, ftrace preemptirq/irq_disable event with user stack trace
option can trigger SEGV in pid 1 which leads to panic.
Reproducer:
CONFIG_PREEMPTIRQ_TRACEPOINTS=y
# echo 1 > events/preemptirq/enable
# echo userstacktrace > trace_options
Output:
Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
CPU: 1 PID: 1 Comm: systemd Not tainted 5.2.0-rc7+ #10
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
Call Trace:
dump_stack+0x67/0x90
panic+0x100/0x2c6
do_exit.cold+0x4e/0x101
do_group_exit+0x3a/0xa0
get_signal+0x14a/0x8e0
do_signal+0x36/0x650
exit_to_usermode_loop+0x92/0xb0
prepare_exit_to_usermode+0x6f/0xb0
retint_user+0x8/0x18
RIP: 0033:0x55be7ad1c89f
Code: Bad RIP value.
RSP: 002b:00007ffe329a4b00 EFLAGS: 00010202
RAX: 0000000000000768 RBX: 00007ffe329a4ba0 RCX: 00007ff0063aa469
RDX: 00007ff0066761de RSI: 00007ffe329a4b20 RDI: 0000000000000768
RBP: 000000000000000b R08: 0000000000000000 R09: 00007ffe329a4e2f
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000768
R13: 0000000000000000 R14: 0000000000000004 R15: 000055be7b3d3560
Kernel Offset: 0x2a000000 from 0xffffffff81000000 (relocation range:
0xffffffff80000000-0xffffffffbfffffff)
Fixes: 02b67518e2b1 ("tracing: add support for userspace stacktraces in
tracing/iter_ctrl")
Signed-off-by: Eiichi Tsukata <de...@etsukata.com>
---
arch/x86/kernel/stacktrace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 2abf27d7df6b..6d0c608ffe34 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -123,12 +123,12 @@ void arch_stack_walk_user(stack_trace_consume_fn
consume_entry, void *cookie,
while (1) {
struct stack_frame_user frame;
+ if ((unsigned long)fp < regs->sp)
+ break;
frame.next_fp = NULL;
frame.ret_addr = 0;
if (!copy_stack_frame(fp, &frame))
break;
- if ((unsigned long)fp < regs->sp)
- break;
if (frame.ret_addr) {
if (!consume_entry(cookie, frame.ret_addr, false))
return;
--
2.21.0
