Re: [PATCH -tip v4 08/12] arm: kprobes: Make a space for regs->ARM_pc at kretprobe_trampoline

Masami Hiramatsu
2021-03-23T00:04:29Z

On Mon, 22 Mar 2021 15:41:18 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Change kretprobe_trampoline to make a space for regs->ARM_pc so that
> kretprobe_trampoline_handler can call instruction_pointer_set()
> safely.

BTW, if kretprobe_trampoline is replaced with the assembly code,
I think it should fill all the regs as much as possible, because
originally it is written by a software break.
Thus the regs->sp should point the stack address at the entry of
kretprobe_trampoline, and also regs->lr and regs->pc will be
kretprobe_trampoline, so that user handler can access caller stack.

Thanks,

>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
> arch/arm/probes/kprobes/core.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
> index 1782b41df095..5f3c2b42787f 100644
> --- a/arch/arm/probes/kprobes/core.c
> +++ b/arch/arm/probes/kprobes/core.c
> @@ -397,11 +397,13 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
> void __naked __kprobes kretprobe_trampoline(void)
> {
> __asm__ __volatile__ (
> + "sub sp, sp, #16 \n\t"
> "stmdb sp!, {r0 - r11} \n\t"
> "mov r0, sp \n\t"
> "bl trampoline_handler \n\t"
> "mov lr, r0 \n\t"
> "ldmia sp!, {r0 - r11} \n\t"
> + "add sp, sp, #16 \n\t"
> #ifdef CONFIG_THUMB2_KERNEL
> "bx lr \n\t"
> #else
>

--
Masami Hiramatsu <mhiramat@kernel.org>