From 7d7b720a4b8049446cffce870b1dd3ffa89d4b40 Mon Sep 17 00:00:00 2001 From: "Madhavan T. Venkataraman" Date: Mon, 10 May 2021 12:00:26 +0100 Subject: arm64: Implement stack trace termination record Reliable stacktracing requires that we identify when a stacktrace is terminated early. We can do this by ensuring all tasks have a final frame record at a known location on their task stack, and checking that this is the final frame record in the chain. We'd like to use task_pt_regs(task)->stackframe as the final frame record, as this is already setup upon exception entry from EL0. For kernel tasks we need to consistently reserve the pt_regs and point x29 at this, which we can do with small changes to __primary_switched, __secondary_switched, and copy_process(). Since the final frame record must be at a specific location, we must create the final frame record in __primary_switched and __secondary_switched rather than leaving this to start_kernel and secondary_start_kernel. Thus, __primary_switched and __secondary_switched will now show up in stacktraces for the idle tasks. Since the final frame record is now identified by its location rather than by its contents, we identify it at the start of unwind_frame(), before we read any values from it. External debuggers may terminate the stack trace when FP == 0. In the pt_regs->stackframe, the PC is 0 as well. So, stack traces taken in the debugger may print an extra record 0x0 at the end. While this is not pretty, this does not do any harm. This is a small price to pay for having reliable stack trace termination in the kernel. That said, gdb does not show the extra record probably because it uses DWARF and not frame pointers for stack traces. Signed-off-by: Madhavan T. Venkataraman Reviewed-by: Mark Brown [Mark: rebase, use ASM_BUG(), update comments, update commit message] Signed-off-by: Mark Rutland Link: https://lore.kernel.org/r/20210510110026.18061-1-mark.rutland@arm.com Signed-off-by: Will Deacon --- arch/arm64/kernel/stacktrace.c | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-) (limited to 'arch/arm64/kernel/stacktrace.c') diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c index de07147a7926..36cf05d5eb9e 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -68,12 +68,16 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) unsigned long fp = frame->fp; struct stack_info info; - if (fp & 0xf) - return -EINVAL; - if (!tsk) tsk = current; + /* Final frame; nothing to unwind */ + if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) + return -ENOENT; + + if (fp & 0xf) + return -EINVAL; + if (!on_accessible_stack(tsk, fp, &info)) return -EINVAL; @@ -128,12 +132,6 @@ 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); -- cgit v1.2.3-59-g8ed1b