We met "bt" cmd on KASAN kernel vmcore display truncated backtraces
like this:
crash> bt
PID: 4131 TASK: ffff8001521df000 CPU: 3 COMMAND: "bash"
#0 [ffff2000224b0cb0] machine_kexec_prepare at ffff2000200bff4c
After digging the root cause, it turns out that arm64_in_kdump_text()
found wrong bt->bptr at "machine_kexec" branch.
Disassemble machine_kexec() of KASAN vmlinux (gcc 7.3.0):
crash> dis -x machine_kexec
0xffff2000200bff50 <machine_kexec>: stp x29, x30, [sp,#-208]!
0xffff2000200bff54 <machine_kexec+0x4>: mov x29, sp
0xffff2000200bff58 <machine_kexec+0x8>: stp x19, x20, [sp,#16]
0xffff2000200bff5c <machine_kexec+0xc>: str x24, [sp,#56]
0xffff2000200bff60 <machine_kexec+0x10>: str x26, [sp,#72]
0xffff2000200bff64 <machine_kexec+0x14>: mov x2, #0x8ab3
0xffff2000200bff68 <machine_kexec+0x18>: add x1, x29, #0x70
0xffff2000200bff6c <machine_kexec+0x1c>: lsr x1, x1, #3
0xffff2000200bff70 <machine_kexec+0x20>: movk x2, #0x41b5, lsl #16
0xffff2000200bff74 <machine_kexec+0x24>: mov x19, #0x200000000000
0xffff2000200bff78 <machine_kexec+0x28>: adrp x3, 0xffff2000224b0000
0xffff2000200bff7c <machine_kexec+0x2c>: movk x19, #0xdfff, lsl #48
0xffff2000200bff80 <machine_kexec+0x30>: add x3, x3, #0xcb0
0xffff2000200bff84 <machine_kexec+0x34>: add x4, x1, x19
0xffff2000200bff88 <machine_kexec+0x38>: stp x2, x3, [x29,#112]
0xffff2000200bff8c <machine_kexec+0x3c>: adrp x2, 0xffff2000200bf000 <swsusp_arch_resume+0x1e8>
0xffff2000200bff90 <machine_kexec+0x40>: add x2, x2, #0xf50
0xffff2000200bff94 <machine_kexec+0x44>: str x2, [x29,#128]
0xffff2000200bff98 <machine_kexec+0x48>: mov w2, #0xf1f1f1f1
0xffff2000200bff9c <machine_kexec+0x4c>: str w2, [x1,x19]
0xffff2000200bffa0 <machine_kexec+0x50>: mov w2, #0xf200
0xffff2000200bffa4 <machine_kexec+0x54>: mov w1, #0xf3f3f3f3
0xffff2000200bffa8 <machine_kexec+0x58>: movk w2, #0xf2f2, lsl #16
0xffff2000200bffac <machine_kexec+0x5c>: stp w2, w1, [x4,#4]
We notice that:
1. machine_kexec() start address is 0xffff2000200bff50
2. the instruction at machine_kexec+0x44 store the same value
0xffff2000200bff50 (comes from 0xffff2000200bf000 + 0xf50)
into stack postion [x29,#128].
When arm64_in_kdump_text() search LR from stack, it met
0xffff2000200bff50 firstly, so got wrong bt->bptr.
We know that the real LR is always great than the start address
of a function, so let's fix it by change the search conditon to
(*ptr > xxx_start) && (*ptr < xxx_end).
Signed-off-by: Ding Hui <dinghui@xxxxxxxxxxxxxx>
---
arm64.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/arm64.c b/arm64.c
index c3e26a3..7e8a7db 100644
--- a/arm64.c
+++ b/arm64.c
@@ -3479,7 +3479,7 @@ arm64_in_kdump_text(struct bt_info *bt, struct arm64_stackframe *frame)
ms = machdep->machspec;
for (ptr = start - 8; ptr >= base; ptr--) {
if (bt->flags & BT_OPT_BACK_TRACE) {
- if ((*ptr >= ms->crash_kexec_start) &&
+ if ((*ptr > ms->crash_kexec_start) &&
(*ptr < ms->crash_kexec_end) &&
INSTACK(*(ptr - 1), bt)) {
bt->bptr = ((ulong)(ptr - 1) - (ulong)base)
@@ -3488,7 +3488,7 @@ arm64_in_kdump_text(struct bt_info *bt, struct arm64_stackframe *frame)
fprintf(fp, "%lx: %lx (crash_kexec)\n", bt->bptr, *ptr);
return TRUE;
}
- if ((*ptr >= ms->crash_save_cpu_start) &&
+ if ((*ptr > ms->crash_save_cpu_start) &&
(*ptr < ms->crash_save_cpu_end) &&
INSTACK(*(ptr - 1), bt)) {
bt->bptr = ((ulong)(ptr - 1) - (ulong)base)
@@ -3498,14 +3498,14 @@ arm64_in_kdump_text(struct bt_info *bt, struct arm64_stackframe *frame)
return TRUE;
}
} else {
- if ((*ptr >= ms->machine_kexec_start) && (*ptr < ms->machine_kexec_end)) {
+ if ((*ptr > ms->machine_kexec_start) && (*ptr < ms->machine_kexec_end)) {
bt->bptr = ((ulong)ptr - (ulong)base)
+ task_to_stackbase(bt->tc->task);
if (CRASHDEBUG(1))
fprintf(fp, "%lx: %lx (machine_kexec)\n", bt->bptr, *ptr);
return TRUE;
}
- if ((*ptr >= ms->crash_kexec_start) && (*ptr < ms->crash_kexec_end)) {
+ if ((*ptr > ms->crash_kexec_start) && (*ptr < ms->crash_kexec_end)) {
/*
* Stash the first crash_kexec frame in case the machine_kexec
* frame is not found.
@@ -3519,7 +3519,7 @@ arm64_in_kdump_text(struct bt_info *bt, struct arm64_stackframe *frame)
}
continue;
}
- if ((*ptr >= ms->crash_save_cpu_start) && (*ptr < ms->crash_save_cpu_end)) {
+ if ((*ptr > ms->crash_save_cpu_start) && (*ptr < ms->crash_save_cpu_end)) {
bt->bptr = ((ulong)ptr - (ulong)base)
+ task_to_stackbase(bt->tc->task);
if (CRASHDEBUG(1))
@@ -3566,7 +3566,7 @@ arm64_in_kdump_text_on_irq_stack(struct bt_info *bt)
for (ptr = start - 8; ptr >= base; ptr--) {
if (bt->flags & BT_OPT_BACK_TRACE) {
- if ((*ptr >= ms->crash_kexec_start) &&
+ if ((*ptr > ms->crash_kexec_start) &&
(*ptr < ms->crash_kexec_end) &&
INSTACK(*(ptr - 1), bt)) {
bt->bptr = ((ulong)(ptr - 1) - (ulong)base) + stackbase;
@@ -3576,7 +3576,7 @@ arm64_in_kdump_text_on_irq_stack(struct bt_info *bt)
FREEBUF(stackbuf);
return TRUE;
}
- if ((*ptr >= ms->crash_save_cpu_start) &&
+ if ((*ptr > ms->crash_save_cpu_start) &&
(*ptr < ms->crash_save_cpu_end) &&
INSTACK(*(ptr - 1), bt)) {
bt->bptr = ((ulong)(ptr - 1) - (ulong)base) + stackbase;
@@ -3587,7 +3587,7 @@ arm64_in_kdump_text_on_irq_stack(struct bt_info *bt)
return TRUE;
}
} else {
- if ((*ptr >= ms->crash_kexec_start) && (*ptr < ms->crash_kexec_end)) {
+ if ((*ptr > ms->crash_kexec_start) && (*ptr < ms->crash_kexec_end)) {
bt->bptr = ((ulong)ptr - (ulong)base) + stackbase;
if (CRASHDEBUG(1))
fprintf(fp, "%lx: %lx (crash_kexec on IRQ stack)\n",
@@ -3595,7 +3595,7 @@ arm64_in_kdump_text_on_irq_stack(struct bt_info *bt)
FREEBUF(stackbuf);
return TRUE;
}
- if ((*ptr >= ms->crash_save_cpu_start) && (*ptr < ms->crash_save_cpu_end)) {
+ if ((*ptr > ms->crash_save_cpu_start) && (*ptr < ms->crash_save_cpu_end)) {
bt->bptr = ((ulong)ptr - (ulong)base) + stackbase;
if (CRASHDEBUG(1))
fprintf(fp, "%lx: %lx (crash_save_cpu on IRQ stack)\n",
--
2.17.1
--
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