On Fri, Apr 04, 2025 at 01:33:11PM -0700, Andrii Nakryiko wrote:

On Thu, Mar 20, 2025 at 4:43 AM Jiri Olsa [off-list ref] wrote:

quoted

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?

ok, will send it separately

Also, how hard would it be to do the same for other nopX instructions?

will check, might be easy

thanks,
jirka

quoted

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