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Wed, 29 Jul 2026 06:29:32 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 29 Jul 2026 15:29:30 +0200 To: Andrey Grodzovsky Cc: bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, song@kernel.org, rostedt@goodmis.org, naveen@kernel.org, davem@davemloft.net, mhiramat@kernel.org, stable@vger.kernel.org, linux-open-source@crowdstrike.com Subject: Re: [RFC PATCH bpf-next 1/3] bpf: mark trampoline ftrace_ops permanent Message-ID: References: <20260729005959.3853865-1-andrey.grodzovsky@crowdstrike.com> <20260729005959.3853865-2-andrey.grodzovsky@crowdstrike.com> Precedence: bulk X-Mailing-List: stable@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: <20260729005959.3853865-2-andrey.grodzovsky@crowdstrike.com> On Tue, Jul 28, 2026 at 08:59:57PM -0400, Andrey Grodzovsky wrote: > kernel.ftrace_enabled=0 silently kills BPF trampolines (fentry/fexit): > attach still succeeds, the hook stops firing with no error, and > re-enabling silently restores it with no indication anything happened. > > This is a regression, not a new gap: BPF trampolines were already > protected against this the same way livepatch protects itself, via > FTRACE_OPS_FL_PERMANENT on the shared trampoline ftrace_ops. That > protection was silently dropped during a later refactoring and never > restored, so this has been broken for years. > > Both the shared direct_ops (CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS > arches) and the per-trampoline ops allocated on other arches (arm64, > s390) are BPF-trampoline-private, not shared with any unrelated > subsystem, so restoring the same unconditional flag is safe and needs > no kernel/trace/ftrace.c changes -- its existing generic sysctl gate > and attach-time refusal already scan the ops list and pick this up > for free. > > Fixes: 00963a2e75a8 ("bpf: Support bpf_trampoline on functions with IPMODIFY (e.g. livepatch)") hum, we did use it before this commit, I completely missed that, thanks Acked-by: Jiri Olsa jirka > Cc: stable@vger.kernel.org > Assisted-by: Claude:claude-sonnet-5 > Signed-off-by: Andrey Grodzovsky > --- > kernel/bpf/trampoline.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c > index 129d07db117e..3d5069091db7 100644 > --- a/kernel/bpf/trampoline.c > +++ b/kernel/bpf/trampoline.c > @@ -224,6 +224,8 @@ void bpf_image_ksym_del(struct bpf_ksym *ksym) > */ > struct ftrace_ops direct_ops = { > .ops_func = bpf_tramp_ftrace_ops_func, > + /* Same protection livepatch gives its own ftrace_ops. */ > + .flags = FTRACE_OPS_FL_PERMANENT, > }; > > static int direct_ops_alloc(struct bpf_trampoline *tr) > @@ -303,6 +305,8 @@ static int direct_ops_alloc(struct bpf_trampoline *tr) > return -ENOMEM; > tr->fops->private = tr; > tr->fops->ops_func = bpf_tramp_ftrace_ops_func; > + /* See the direct_ops initializer above for why. */ > + tr->fops->flags |= FTRACE_OPS_FL_PERMANENT; > return 0; > } > > -- > 2.34.1 >