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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id wb8-20020a170907d50800b00a3d9b0e41e6sm1127715ejc.205.2024.02.17.09.14.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 17 Feb 2024 09:14:18 -0800 (PST) Message-ID: Subject: Re: [RFC PATCH v1 05/14] bpf: Implement BPF exception frame descriptor generation From: Eduard Zingerman To: Kumar Kartikeya Dwivedi Cc: bpf@vger.kernel.org, Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , David Vernet , Tejun Heo , Raj Sahu , Dan Williams , Rishabh Iyer , Sanidhya Kashyap Date: Sat, 17 Feb 2024 19:14:17 +0200 In-Reply-To: References: <20240201042109.1150490-1-memxor@gmail.com> <20240201042109.1150490-6-memxor@gmail.com> <4ef073e2cf3f5b3c7094e81593001ff068ee9f64.camel@gmail.com> Autocrypt: addr=eddyz87@gmail.com; prefer-encrypt=mutual; keydata=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 nYzhLWGcczc6J71q1Dje0l5vIPaSFOgwmWD4DA+WvuxM/shH4rtWeodbv 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 t1iq+gsfnXbPz5AnS598ScZI1oP7OrPSFJkt/z4acEbOQDQs8aUqrd46PV jsdqGvKnXZxzylux29UTNby4jTlz9pNJM+wPrDRmGfchLDUmf6CffaUYCbu4FiId+9+dcTCDvxbABRy1C3OJ8QY7cxfJ+pEZW18fRJ0XCl/fiV/ecAOfB3HsqgTzAn555h0rkFgay0hAvMU/mAW/CFNSIxV397zm749ZNLA0L2dMy1AKuOqH+/B+/ImBfJMDjmdyJQ8WU/OFRuGLdqOd2oZrA1iuPIa+yUYyZkaZfz/emQwpIL1+Q4p1R/OplA4yc301AqruXXUcVDbEB+joHW3hy5FwK5t5OwTKatrSJBkydSF9zdXy98fYzGniRyRA65P0Ix/8J3BYB4edY2/w0Ip/mdYsYQljBY0A== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2024-02-16 at 23:06 +0100, Kumar Kartikeya Dwivedi wrote: [...] > I will add tests to exercise these cases, but the idea for STACK_ZERO > was to treat it as if we had a NULL value in that stack slot, thus > allowing merging with other resource pointers. Sometimes when NULL > initializing something, it can be marked as STACK_ZERO in the verifier > state. Therefore, we would prefer to treat it same as the case where a > scalar reg known to be zero is spilled to the stack (that is what we > do by using a fake struct bpf_reg_state). Agree that it is useful to merge 0/NULL/STACK_ZERO with PTR_TO_SOMETHING. What I meant is that merging with 0 is a noop and there is no need to add a new fd entry. However, I missed the following check: + static int gen_exception_frame_desc_reg_entry(struct bpf_verifier_env *en= v, struct bpf_reg_state *reg, int off, int frameno) + { + struct bpf_frame_desc_reg_entry fd =3D {}; +=20 + if ((!reg->ref_obj_id && reg->type !=3D NOT_INIT) || reg->type =3D=3D SC= ALAR_VALUE) + return 0; So, the intent is to skip adding fd entry if register has scalar type, righ= t? I tried the following test case: SEC("?tc") __success int test(struct __sk_buff *ctx) { asm volatile ( "r7 =3D *(u32 *)(r1 + 0); \ r1 =3D %[ringbuf] ll; \ r2 =3D 8; \ r3 =3D 0; \ r0 =3D 0; \ if r7 > 42 goto +1; \ call %[bpf_ringbuf_reserve]; \ *(u64 *)(r10 - 8) =3D r0; \ r0 =3D 0; \ r1 =3D 0; \ call bpf_throw; \ " : : __imm(bpf_ringbuf_reserve), __imm_addr(ringbuf) : "memory"); return 0; } And it adds fp[-8] entry for one branch and skips fp[-8] for the other. However, the following test passes as well (note 'r0 =3D 7'): SEC("?tc") __success int same_resource_many_regs(struct __sk_buff *ctx) { asm volatile ( "r7 =3D *(u32 *)(r1 + 0); \ r1 =3D %[ringbuf] ll; \ r2 =3D 8; \ r3 =3D 0; \ r0 =3D 7; /* !!! */ \ if r7 > 42 goto +1; \ call %[bpf_ringbuf_reserve]; \ *(u64 *)(r10 - 8) =3D r0; \ r0 =3D 0; \ r1 =3D 0; \ call bpf_throw; \ " : : __imm(bpf_ringbuf_reserve), __imm_addr(ringbuf) : "memory"); return 0; } Which is probably not correct, as scalar 7 would be used as a parameter for ringbuf destructor, right?