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Tue, 27 May 2025 17:15:33 -0700 (PDT) Received: from ezingerman-mba ([2620:10d:c090:500::7:461c]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-234cc2336b8sm1686695ad.159.2025.05.27.17.15.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 May 2025 17:15:33 -0700 (PDT) From: Eduard Zingerman To: Kumar Kartikeya Dwivedi Cc: bpf@vger.kernel.org, Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Emil Tsalapatis , Barret Rhoden , Matt Bobrowski , kkd@meta.com, kernel-team@meta.com Subject: Re: [PATCH bpf-next v2 04/11] bpf: Hold RCU read lock in bpf_prog_ksym_find In-Reply-To: (Kumar Kartikeya Dwivedi's message of "Sat, 24 May 2025 06:41:08 +0200") References: <20250524011849.681425-1-memxor@gmail.com> <20250524011849.681425-5-memxor@gmail.com> Date: Tue, 27 May 2025 17:15:31 -0700 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Kumar Kartikeya Dwivedi writes: [...] >> --- a/kernel/bpf/core.c >> +++ b/kernel/bpf/core.c >> @@ -782,7 +782,11 @@ bool is_bpf_text_address(unsigned long addr) >> >> struct bpf_prog *bpf_prog_ksym_find(unsigned long addr) >> { >> - struct bpf_ksym *ksym = bpf_ksym_find(addr); >> + struct bpf_ksym *ksym; >> + >> + rcu_read_lock(); >> + ksym = bpf_ksym_find(addr); >> + rcu_read_unlock(); >> >> return ksym && ksym->prog ? >> container_of(ksym, struct bpf_prog_aux, ksym)->prog : > > This isn't right, we need to have the read section open around ksym > access as well. > We can end the section and return the prog pointer. > The caller is responsible to ensure prog outlives RCU protection, or > otherwise hold it if necessary for prog's lifetime. > > We're using this to pick programs who have an active stack frame, so > they aren't going away. > But the ksym access itself needs to happen under correct protection. > > I can fix it in a respin, whatever is best. Are rcu_read_{lock,unlock} necessary in core.c:search_bpf_extables() after this change? Also, helpers.c:bpf_stack_walker.c does not have lock/unlock in it, this patch needs a fixes tag for commit f18b03fabaa9 ("bpf: Implement BPF exceptions")?