Re: [PATCH RFCv3 10/23] uprobes/x86: Add support to emulate nop5 instruction

Andrii Nakryiko
2025-04-04T20:33:33Z

On Thu, Mar 20, 2025 at 4:43 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Adding support to emulate nop5 as the original uprobe instruction.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> arch/x86/kernel/uprobes.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>

This optimization is independent from the sys_uprobe, right? Maybe
send it as a stand-alone patch and let's land it sooner?
Also, how hard would it be to do the same for other nopX instructions?

> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index 5ee2cce4c63e..1661e0ab2a3d 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -308,6 +308,11 @@ static int uprobe_init_insn(struct arch_uprobe *auprobe, struct insn *insn, bool
> return -ENOTSUPP;
> }
>
> +static int is_nop5_insn(uprobe_opcode_t *insn)
> +{
> + return !memcmp(insn, x86_nops[5], 5);
> +}
> +
> #ifdef CONFIG_X86_64
>
> asm (
> @@ -865,6 +870,11 @@ void arch_uprobe_clear_state(struct mm_struct *mm)
> hlist_for_each_entry_safe(tramp, n, &state->head_tramps, node)
> destroy_uprobe_trampoline(tramp);
> }
> +
> +static bool emulate_nop5_insn(struct arch_uprobe *auprobe)
> +{
> + return is_nop5_insn((uprobe_opcode_t *) &auprobe->insn);
> +}
> #else /* 32-bit: */
> /*
> * No RIP-relative addressing on 32-bit
> @@ -878,6 +888,10 @@ static void riprel_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> static void riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> {
> }
> +static bool emulate_nop5_insn(struct arch_uprobe *auprobe)
> +{
> + return false;
> +}
> #endif /* CONFIG_X86_64 */
>
> struct uprobe_xol_ops {
> @@ -1109,6 +1123,8 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
> break;
>
> case 0x0f:
> + if (emulate_nop5_insn(auprobe))
> + goto setup;
> if (insn->opcode.nbytes != 2)
> return -ENOSYS;
> /*
> --
> 2.49.0
>