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[37.188.160.213]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43cf245f8a3sm18972239f8f.24.2026.03.30.02.28.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Mar 2026 02:28:49 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 30 Mar 2026 11:28:46 +0200 To: Leon Hwang Cc: bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Shuah Khan , Feng Yang , Toke Hoiland-Jorgensen , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-patches-bot@fb.com Subject: Re: [PATCH bpf-next v2 1/2] bpf: Fix abuse of kprobe_write_ctx via freplace Message-ID: References: <20260326141718.17731-1-leon.hwang@linux.dev> <20260326141718.17731-2-leon.hwang@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260326141718.17731-2-leon.hwang@linux.dev> On Thu, Mar 26, 2026 at 10:17:17PM +0800, Leon Hwang wrote: > uprobe programs are allowed to modify struct pt_regs. > > Since the actual program type of uprobe is KPROBE, it can be abused to > modify struct pt_regs via kprobe+freplace when the kprobe attaches to > kernel functions. > > For example, > > SEC("?kprobe") > int kprobe(struct pt_regs *regs) > { > return 0; > } > > SEC("?freplace") > int freplace_kprobe(struct pt_regs *regs) > { > regs->di = 0; > return 0; > } > > freplace_kprobe prog will attach to kprobe prog. > kprobe prog will attach to a kernel function. > > Without this patch, when the kernel function runs, its first arg will > always be set as 0 via the freplace_kprobe prog. > > To fix the abuse of kprobe_write_ctx=true via kprobe+freplace, disallow > attaching freplace programs on kprobe programs with different > kprobe_write_ctx values. > > Fixes: 7384893d970e ("bpf: Allow uprobe program to change context registers") > Signed-off-by: Leon Hwang > --- > kernel/bpf/syscall.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index 51ade3cde8bb..1dd2ea076d8b 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -3733,6 +3733,11 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog, > tr = prog->aux->dst_trampoline; > tgt_prog = prog->aux->dst_prog; > } could you please put some comment in here explaining the check, with that Acked-by: Jiri Olsa thanks, jirka > + if (prog->type == BPF_PROG_TYPE_EXT && > + prog->aux->kprobe_write_ctx != tgt_prog->aux->kprobe_write_ctx) { > + err = -EINVAL; > + goto out_unlock; > + } > > err = bpf_link_prime(&link->link.link, &link_primer); > if (err) > -- > 2.53.0 >