linux-kernel - Re: [PATCHv2 perf/core 1/2] uprobes/x86: Add support to emulate nop instructions

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAEf4BzbvMYJf5LLxwamYpzzu=Sewzti-FR-9o4AGfU+KZu0b1Q@mail.gmail.com>
Date: Fri, 11 Apr 2025 09:02:10 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	x86@...nel.org, Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, 
	John Fastabend <john.fastabend@...il.com>, Hao Luo <haoluo@...gle.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Alan Maguire <alan.maguire@...cle.com>
Subject: Re: [PATCHv2 perf/core 1/2] uprobes/x86: Add support to emulate nop instructions

On Fri, Apr 11, 2025 at 5:18 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Adding support to emulate all nop instructions as the original uprobe
> instruction.
>
> This change speeds up uprobe on top of all nop instructions and is a
> preparation for usdt probe optimization, that will be done on top of
> nop5 instruction.
>
> With this change the usdt probe on top of nop5 won't take the performance
> hit compared to usdt probe on top of standard nop instruction.
>
> Suggested-by: Oleg Nesterov <oleg@...hat.com>
> Suggested-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
> v2 changes:
> - follow Adndrii/Oleg's suggestion and emulate all the nops
>
>  arch/x86/kernel/uprobes.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index 9194695662b2..262960189a1c 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -840,6 +840,12 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
>         insn_byte_t p;
>         int i;
>
> +       /* x86_nops[i]; same as jmp with .offs = 0 */
> +       for (i = 1; i <= ASM_NOP_MAX; ++i) {

i <= ASM_NOP_MAX && i <= insn->length

?

otherwise what prevents us from reading past the actual instruction bytes?


or, actually, shouldn't we just check memcmp(x86_nops[insn->length])
if insn->length < ASM_NOP_MAX ?


> +               if (!memcmp(insn->kaddr, x86_nops[i], i))
> +                       goto setup;
> +       }
> +
>         switch (opc1) {
>         case 0xeb:      /* jmp 8 */
>         case 0xe9:      /* jmp 32 */
> --
> 2.49.0
>