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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id k40-20020a05600c1ca800b0040b45356b72sm11444693wms.33.2023.12.10.02.30.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 10 Dec 2023 02:30:41 -0800 (PST) Message-ID: <8e45c28fa0827be2b01a7cd36aa68750ceff69f5.camel@gmail.com> Subject: Re: [PATCH bpf-next 6/7] libbpf: BPF Static Keys support From: Eduard Zingerman To: Yonghong Song , Alexei Starovoitov , Anton Protopopov Cc: Andrii Nakryiko , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Jiri Olsa , Martin KaFai Lau , Stanislav Fomichev , bpf Date: Sun, 10 Dec 2023 12:30:38 +0200 In-Reply-To: <3682c649-6a6a-4f66-b4fa-fbcbb774ae94@linux.dev> References: <20231206141030.1478753-1-aspsk@isovalent.com> <20231206141030.1478753-7-aspsk@isovalent.com> <85aa91f9-d5c0-4e7b-950d-475da7787f64@linux.dev> <3682c649-6a6a-4f66-b4fa-fbcbb774ae94@linux.dev> 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 3.50.1 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 How about a slightly different modification of the Anton's idea. Suppose that, as before, there is a special map type: struct { __uint(type, BPF_MAP_TYPE_ARRAY); __type(key, __u32); __type(value, __u32); __uint(map_flags, BPF_F_STATIC_KEY); __uint(max_entries, 1); } skey1 SEC(".maps") Which is used as below: __attribute__((naked)) int foo(void) { asm volatile ( "r0 =3D %[skey1] ll;" "if r0 !=3D r0 goto 1f;" "r1 =3D r10;" "r1 +=3D -8;" "r2 =3D 1;" "call %[bpf_trace_printk];" "1:" "exit;" :: __imm_addr(skey1), __imm(bpf_trace_printk) : __clobber_all ); } Disassembly of section .text: 0000000000000000 : 0: r0 =3D 0x0 ll 0000000000000000: R_BPF_64_64 skey1 ;; <---- Map relocation as u= sual 2: if r0 =3D=3D r0 goto +0x4 ;; <---- Note condition 3: r1 =3D r10 4: r1 +=3D -0x8 5: r2 =3D 0x1 6: call 0x6 7: exit And suppose that verifier is modified in the following ways: - treat instructions "if rX =3D=3D rX" / "if rX !=3D rX" (when rX points to static key map) in a special way: - when program is verified, the jump is considered non deterministic; - when program is jitted, the jump is compiled as nop for "!=3D" and as unconditional jump for "=3D=3D"; - build a table of static keys based on a specific map referenced in condition, e.g. for the example above it can be inferred that insn 2 associates with map skey1 because "r0" points to "skey1"; - jit "rX =3D ll;" as nop; On the plus side: - any kinds of jump tables are omitted from system call; - no new instruction is needed; - almost no modifications to libbpf are necessary (only a helper macro to convince clang to keep "if rX =3D=3D rX"); What do you think? Thanks, Eduard