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([2620:10d:c090:500::7:fbb7]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-33e96d497e1sm939793eec.25.2026.09.22.14.43.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Sep 2026 14:43:03 -0700 (PDT) Message-ID: Subject: Re: [PATCH bpf-next v4 07/20] bpf: Refuse exception cleanup shapes bpf_throw() cannot dispatch From: Eduard Zingerman To: Yonghong Song , bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , kernel-team@fb.com Date: Tue, 22 Sep 2026 14:43:02 -0700 In-Reply-To: <73a766ca-8198-4677-8c29-29fac8489f73@linux.dev> References: <20260921210033.1715000-1-yonghong.song@linux.dev> <20260921210109.1719713-1-yonghong.song@linux.dev> <73a766ca-8198-4677-8c29-29fac8489f73@linux.dev> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2026-09-21 at 20:45 -0700, Yonghong Song wrote: ... > > Why is it necessary to hand-roll a CFG traversal and a separate pass > > for this check? Given that bpf verifier state already maintains > > `unwinding' flag, the instructions properties can be checked from > > do_check_insn(), e.g.: > > - bpf_throw() -- reject if unwinding > > - call to a throwing global -- reject if unwinding > > - bpf_unwind_resume() -- require unwinding and the pad-owning fra= me > > - BPF_EXIT -- reject in the pad-owning frame, allow in= callees > > - LD_{ABS,IND} -- reject if unwinding > >=20 > > I think that would take much less code, wdyt? >=20 > This is a good idea. Let me try. Thanks! Also, regarding the tail calls. It appears that the following chain can call bpf_throw from a landing pad: bpf_throw() -> landing pad -> global procedure call -> tail call -> bpf_t= hrow() would this work as expected?