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[192.26.29.3]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47ff7b250e5sm4676930f8f.27.2026.08.06.02.02.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Aug 2026 02:02:53 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Thu, 06 Aug 2026 11:02:52 +0200 Message-Id: Cc: "Puranjay Mohan" , , "Puranjay Mohan" Subject: Re: [PATCH bpf-next v2 0/2] bpf: Invalidate RCU pointers after final spin unlock From: "Kumar Kartikeya Dwivedi" To: "Ning Ding" , X-Mailer: aerc 0.21.0 References: <20260803112615.3362122-1-dingning04@gmail.com> In-Reply-To: On Wed Aug 5, 2026 at 9:00 AM CEST, Ning Ding wrote: >> > 1. Disabling preemption >> > 2. Disabling bottom halves >> > 3. Disabling interrupts >> > 4. Acquiring a spin lock >> > >> > As you are doing it for 4, can you also do it for 1 and 3? I don't thi= nk >> > BPF can disable bottom halves right now. > > Hi, I have written the follow-up patch to account for > preemption-disabled and irq-disabled regions. But still working on the > selftests. > While checking rcu gaps, I also found what looks like a separate issue > for state pruning also regarding the MEM_RCU and PTR_UNTRUSTED. A > sample example is: > > bpf_rcu_read_lock(); > bpf_iter_task_new(&it, NULL, BPF_TASK_ITER_ALL_PROCS); > > if (condition) { > /* Safe: the outer RCU lock remains active. */ > bpf_rcu_read_lock(); > bpf_rcu_read_unlock(); > } else { > /* Unsafe: protection reaches zero, creating an unguarded gap. */ > bpf_rcu_read_unlock(); > bpf_rcu_read_lock(); > } > > /* Both branches have one active RCU lock here. */ > bpf_iter_task_next(&it); > bpf_rcu_read_unlock(); > > But STACK_ITER comparison in stacksafe() does not compare > spilled_ptr.type. So the verifier considers the trusted and untrusted > iterator states are equivalent. It can possibly prune the unsafe path > before is_iter_reg_valid_init() rejects it. > Sounds plausible. Once you have a fix and test that triggers bad pruning behavior reliably, please send it as a patch set. > https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/ker= nel/bpf/states.c?id=3D6655c409707ec8ce9ce0850ffe4fe02331fd4d9c#n806