On Mon, 3 May 2021 at 19:38, <madvenka@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: "Madhavan T. Venkataraman" <madvenka@xxxxxxxxxxxxxxxxxxx>
>
> Create a sym_code_ranges[] array to cover the following text sections that
> contain functions defined as SYM_CODE_*(). These functions are low-level
> functions (and do not have a proper frame pointer prolog and epilog). So,
> they are inherently unreliable from a stack unwinding perspective.
>
> .entry.text
> .idmap.text
> .hyp.idmap.text
> .hyp.text
> .hibernate_exit.text
> .entry.tramp.text
>
> If a return PC falls in any of these, mark the stack trace unreliable.
>
> The only exception to this is - if the unwinder has reached the last
> frame already, it will not mark the stack trace unreliable since there
> is no more unwinding to do. E.g.,
>
> - ret_from_fork() occurs at the end of the stack trace of
> kernel tasks.
>
> - el0_*() functions occur at the end of EL0 exception stack
> traces. This covers all user task entries into the kernel.
>
> NOTE:
> - EL1 exception handlers are in .entry.text. So, stack traces that
> contain those functions will be marked not reliable. This covers
> interrupts, exceptions and breakpoints encountered while executing
> in the kernel.
>
> - At the end of an interrupt, the kernel can preempt the current
> task if required. So, the stack traces of all preempted tasks will
> show the interrupt frame and will be considered unreliable.
>
> Signed-off-by: Madhavan T. Venkataraman <madvenka@xxxxxxxxxxxxxxxxxxx>
> ---
> arch/arm64/kernel/stacktrace.c | 54 ++++++++++++++++++++++++++++++++++
> 1 file changed, 54 insertions(+)
>
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index c21a1bca28f3..1ff14615a55a 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -15,9 +15,48 @@
>
> #include <asm/irq.h>
> #include <asm/pointer_auth.h>
> +#include <asm/sections.h>
> #include <asm/stack_pointer.h>
> #include <asm/stacktrace.h>
>
> +struct code_range {
> + unsigned long start;
> + unsigned long end;
> +};
> +
> +struct code_range sym_code_ranges[] =
This should be static and const
> +{
> + /* non-unwindable ranges */
> + { (unsigned long)__entry_text_start,
> + (unsigned long)__entry_text_end },
> + { (unsigned long)__idmap_text_start,
> + (unsigned long)__idmap_text_end },
> + { (unsigned long)__hyp_idmap_text_start,
> + (unsigned long)__hyp_idmap_text_end },
> + { (unsigned long)__hyp_text_start,
> + (unsigned long)__hyp_text_end },
> +#ifdef CONFIG_HIBERNATION
> + { (unsigned long)__hibernate_exit_text_start,
> + (unsigned long)__hibernate_exit_text_end },
> +#endif
> +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
> + { (unsigned long)__entry_tramp_text_start,
> + (unsigned long)__entry_tramp_text_end },
> +#endif
> + { /* sentinel */ }
> +};
> +
> +static struct code_range *lookup_range(unsigned long pc)
const struct code_range *
> +{
> + struct code_range *range;
const struct code_range *
> +
> + for (range = sym_code_ranges; range->start; range++) {
> + if (pc >= range->start && pc < range->end)
> + return range;
> + }
> + return range;
> +}
> +
> /*
> * AArch64 PCS assigns the frame pointer to x29.
> *
> @@ -43,6 +82,7 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
> {
> unsigned long fp = frame->fp;
> struct stack_info info;
> + struct code_range *range;
const struct code_range *
>
> frame->reliable = true;
>
> @@ -103,6 +143,8 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
> return 0;
> }
>
> + range = lookup_range(frame->pc);
> +
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> if (tsk->ret_stack &&
> frame->pc == (unsigned long)return_to_handler) {
> @@ -118,9 +160,21 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
> return -EINVAL;
> frame->pc = ret_stack->ret;
> frame->pc = ptrauth_strip_insn_pac(frame->pc);
> + return 0;
> }
> #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
>
> + if (!range->start)
> + return 0;
> +
> + /*
> + * The return PC falls in an unreliable function. If the final frame
> + * has been reached, no more unwinding is needed. Otherwise, mark the
> + * stack trace not reliable.
> + */
> + if (frame->fp)
> + frame->reliable = false;
> +
> return 0;
> }
> NOKPROBE_SYMBOL(unwind_frame);
> --
> 2.25.1
>
>
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