From: Mark Rutland mark.rutland@arm.com
[ 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@arm.com Fixes: 6106e1112cc6 ("arm64: remove EL0 exception frame record") Reported-by: Leo Yan leo.yan@linaro.org Tested-by: Leo Yan leo.yan@linaro.org Cc: Will Deacon will@kernel.org Cc: Mark Brown broonie@kernel.org Cc: "Madhavan T. Venkataraman" madvenka@linux.microsoft.com Link: https://lore.kernel.org/r/20210429104813.GA33550@C02TD0UTHF1T.local Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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);