[PATCH RESEND] arm64: remove EL0 exception frame record
From: Mark Brown <broonie@kernel.org>
Date: 2021-01-13 17:37:12
From: Mark Rutland <mark.rutland@arm.com>
When entering an exception from EL0, the entry code creates a synthetic
frame record with a NULL PC. This was used by the code introduced in
commit:
7326749801396105 ("arm64: unwind: reference pt_regs via embedded stack frame")
... to discover exception entries on the stack and dump the associated
pt_regs. Since the NULL PC was undesirable for the stacktrace, we added
a special case to unwind_frame() to prevent the NULL PC from being
logged.
Since commit:
a25ffd3a6302a678 ("arm64: traps: Don't print stack or raw PC/LR values in backtraces")
... we no longer try to dump the pt_regs as part of a stacktrace, and
hence no longer need the synthetic exception record.
This patch removes the synthetic exception record and the associated
special case in unwind_frame(). Instead, EL0 exceptions set the FP to
NULL, as is the case for other terminal records (e.g. when a kernel
thread starts). The synthetic record for exceptions from EL1 is
retrained as this has useful unwind information for the interrupted
context.
To make the terminal case a bit clearer, an explicit check is added to
the start of unwind_frame(). This would otherwise be caught implicitly
by the on_accessible_stack() checks.
Reported-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
This was previously sent as part of a bigger series that I'm currently
working on revising but seems to make sense from a documentation and
clarity point independently.
arch/arm64/kernel/entry.S | 10 +++++-----
arch/arm64/kernel/stacktrace.c | 13 ++++---------
2 files changed, 9 insertions(+), 14 deletions(-)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index a8c3e7aaca74..2db9804a9035 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S@@ -261,16 +261,16 @@ alternative_else_nop_endif stp lr, x21, [sp, #S_LR] /* - * In order to be able to dump the contents of struct pt_regs at the - * time the exception was taken (in case we attempt to walk the call - * stack later), chain it together with the stack frames. + * For exceptions from EL0, terminate the callchain here. + * For exceptions from EL1, create a synthetic frame record so the + * interrupted code shows up in the backtrace. */ .if \el == 0 - stp xzr, xzr, [sp, #S_STACKFRAME] + mov x29, xzr .else stp x29, x22, [sp, #S_STACKFRAME] - .endif add x29, sp, #S_STACKFRAME + .endif #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 fa56af1a59c3..0fb42129b469 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c@@ -44,6 +44,10 @@ 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 -EINVAL; + if (fp & 0xf) return -EINVAL;
@@ -104,15 +108,6 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) frame->pc = ptrauth_strip_insn_pac(frame->pc); - /* - * Frames created upon entry from EL0 have NULL FP and PC values, so - * don't bother reporting these. Frames created by __noreturn functions - * might have a valid FP even if PC is bogus, so only terminate where - * both are NULL. - */ - if (!frame->fp && !frame->pc) - return -EINVAL; - return 0; } NOKPROBE_SYMBOL(unwind_frame);
--
2.20.1
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel