From: Mark Rutland <mark.rutland@xxxxxxx>
[ Upstream commit 8533d5bfad41e74b7dd80d292fd484913cdfb374 ]
We removed the terminal frame records in commit:
6106e1112cc69a36 ("arm64: remove EL0 exception frame record")
... on the assumption that as we no longer used them to find the pt_regs
at exception boundaries, they were no longer necessary.
However, Leo reports that as an unintended side-effect, this causes
traces which cross secondary_start_kernel to terminate one entry too
late, with a spurious "0" entry.
There are a few ways we could sovle this, but as we're planning to use
terminal records for RELIABLE_STACKTRACE, let's revert the logic change
for now, keeping the update comments and accounting for the changes in
commit:
3c02600144bdb0a1 ("arm64: stacktrace: Report when we reach the end of the stack")
This is effectively a partial revert of commit:
6106e1112cc69a36 ("arm64: remove EL0 exception frame record")
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Fixes: 6106e1112cc6 ("arm64: remove EL0 exception frame record")
Reported-by: Leo Yan <leo.yan@xxxxxxxxxx>
Tested-by: Leo Yan <leo.yan@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Cc: "Madhavan T. Venkataraman" <madvenka@xxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210429104813.GA33550@C02TD0UTHF1T.local
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/arm64/kernel/entry.S | 6 +++---
arch/arm64/kernel/stacktrace.c | 10 ++++++----
2 files changed, 9 insertions(+), 7 deletions(-)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 6acfc5e6b5e0..9b205744a233 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -263,16 +263,16 @@ alternative_else_nop_endif
stp lr, x21, [sp, #S_LR]
/*
- * For exceptions from EL0, terminate the callchain here.
+ * For exceptions from EL0, create a terminal frame record.
* For exceptions from EL1, create a synthetic frame record so the
* interrupted code shows up in the backtrace.
*/
.if \el == 0
- mov x29, xzr
+ stp xzr, xzr, [sp, #S_STACKFRAME]
.else
stp x29, x22, [sp, #S_STACKFRAME]
- add x29, sp, #S_STACKFRAME
.endif
+ add x29, sp, #S_STACKFRAME
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
alternative_if_not ARM64_HAS_PAN
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index d55bdfb7789c..7032a5f9e624 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -44,10 +44,6 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
unsigned long fp = frame->fp;
struct stack_info info;
- /* Terminal record; nothing to unwind */
- if (!fp)
- return -ENOENT;
-
if (fp & 0xf)
return -EINVAL;
@@ -108,6 +104,12 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
frame->pc = ptrauth_strip_insn_pac(frame->pc);
+ /*
+ * This is a terminal record, so we have finished unwinding.
+ */
+ if (!frame->fp && !frame->pc)
+ return -ENOENT;
+
return 0;
}
NOKPROBE_SYMBOL(unwind_frame);
--
2.30.2
