linux-kernel - Re: [PATCH bpf-next v3 1/3] bpf, x86: inline bpf_get_current_task() for x86

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] [day] [month] [year] [list]

Message-ID: <3031509.e9J7NaK4W3@7950hx>
Date: Sat, 10 Jan 2026 11:43:47 +0800
From: Menglong Dong <menglong.dong@...ux.dev>
To: ast@...nel.org, eddyz87@...il.com,
 Menglong Dong <menglong8.dong@...il.com>
Cc: daniel@...earbox.net, john.fastabend@...il.com, andrii@...nel.org,
 martin.lau@...ux.dev, song@...nel.org, yonghong.song@...ux.dev,
 kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org,
 bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 1/3] bpf,
 x86: inline bpf_get_current_task() for x86_64

On 2026/1/9 16:26, Menglong Dong wrote:
> Inline bpf_get_current_task() and bpf_get_current_task_btf() for x86_64
> to obtain better performance.
> 
> In !CONFIG_SMP case, the percpu variable is just a normal variable, and
> we can read the current_task directly.
> 
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> ---
> v3:
> - implement it in the verifier with BPF_MOV64_PERCPU_REG() instead of in
>   x86_64 JIT.
> ---
>  kernel/bpf/verifier.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 3d44c5d06623..520c413839ee 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -17688,6 +17688,8 @@ static bool verifier_inlines_helper_call(struct bpf_verifier_env *env, s32 imm)
>  	switch (imm) {
>  #ifdef CONFIG_X86_64
>  	case BPF_FUNC_get_smp_processor_id:
> +	case BPF_FUNC_get_current_task_btf:
> +	case BPF_FUNC_get_current_task:
>  		return env->prog->jit_requested && bpf_jit_supports_percpu_insn();
>  #endif
>  	default:
> @@ -23273,6 +23275,24 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
>  			insn      = new_prog->insnsi + i + delta;
>  			goto next_insn;
>  		}
> +
> +		/* Implement bpf_get_current_task() and bpf_get_current_task_btf() inline. */
> +		if ((insn->imm == BPF_FUNC_get_current_task || insn->imm == BPF_FUNC_get_current_task_btf) &&
> +		    verifier_inlines_helper_call(env, insn->imm)) {
> +			insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, (u32)(unsigned long)&current_task);

The !CONFIG_SMP case is still not handled properly here.
In the CONFIG_SMP case, I think &current_task is always
u32, so we can remove the casting. Therefore, this code
will be suitable for !CONFIG_SMP too.

> +			insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);

In !CONFIG_SMP case, &current_task is a normal variable
pointer, and the BPF_MOV64_PERCPU_REG() will be ignored,
which makes the whole logic right.

I'll do more testing on it.

> +			insn_buf[2] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
> +			cnt = 3;
> +
> +			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
> +			if (!new_prog)
> +				return -ENOMEM;
> +
> +			delta    += cnt - 1;
> +			env->prog = prog = new_prog;
> +			insn      = new_prog->insnsi + i + delta;
> +			goto next_insn;
> +		}
>  #endif
>  		/* Implement bpf_get_func_arg inline. */
>  		if (prog_type == BPF_PROG_TYPE_TRACING &&
>