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arm64: stacktrace: restore terminal records 

We removed the terminal frame records in commit:

   6106e1112c ("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:

  3c02600144 ("arm64: stacktrace: Report when we reach the end of the stack")

This is effectively a partial revert of commit:

  6106e1112c ("arm64: remove EL0 exception frame record")

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Fixes: 6106e1112c ("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>
This commit is contained in:
Mark Rutland 2021-04-29 11:20:04 +01:00 committed by Catalin Marinas
parent 388708028e
commit 8533d5bfad
2 changed files with 9 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
arch/arm64/kernel/entry.S
View File

@ -283,16 +283,16 @@ 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

10
arch/arm64/kernel/stacktrace.c
View File

@ -68,10 +68,6 @@ 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;
@ -132,6 +128,12 @@ 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);