OK. I will make all the changes you suggested.
Thanks!
Madhavan
On 5/5/21 2:30 PM, Ard Biesheuvel wrote:
> 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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>> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
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