On Fri, 19 Mar 2021 21:23:12 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> To simplify the stacktrace with pt_regs from kretprobe handler,
> set the correct return address to the instruction pointer in
> the pt_regs before calling kretprobe handlers.
>
Oops, now I also find this breaks kretprobe for arm. It seems
not enough registers stores. I need to fix the arm kprobe code
too.
In arch/arm/include/uapi/asm/ptrace.h,
---
#define ARM_pc uregs[15]
---
And in arch/arm/probes/kprobes/core.c,
---
/*
* When a retprobed function returns, trampoline_handler() is called,
* calling the kretprobe's handler. We construct a struct pt_regs to
* give a view of registers r0-r11 to the user return-handler. This is
* not a complete pt_regs structure, but that should be plenty sufficient
* for kretprobe handlers which should normally be interested in r0 only
* anyway.
*/
void __naked __kprobes kretprobe_trampoline(void)
{
__asm__ __volatile__ (
"stmdb sp!, {r0 - r11} \n\t"
---
So, changing regs->ARM_pc will break a stack entry. I need to expand
it to r15.
Thanks,
> Suggested-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> ---
> Changes in v3:
> - Cast the correct_ret_addr to unsigned long.
> ---
> kernel/kprobes.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index cf19edc038e4..4ce3e6f5d28d 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1914,6 +1914,9 @@ unsigned long __kretprobe_trampoline_handler(struct pt_regs *regs,
> BUG_ON(1);
> }
>
> + /* Set the instruction pointer to the correct address */
> + instruction_pointer_set(regs, (unsigned long)correct_ret_addr);
> +
> /* Run them. */
> first = current->kretprobe_instances.first;
> while (first) {
>
--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>
