From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 69-171-232-180.mail-mxout.facebook.com (69-171-232-180.mail-mxout.facebook.com [69.171.232.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E489615AD2 for ; Tue, 2 Jan 2024 19:07:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=linux.dev Received: by devbig309.ftw3.facebook.com (Postfix, from userid 128203) id 191E62C3C8262; Tue, 2 Jan 2024 11:07:26 -0800 (PST) From: Yonghong Song To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , kernel-team@fb.com, Martin KaFai Lau , Kuniyuki Iwashima , Martin KaFai Lau Subject: [PATCH bpf-next] bpf: Track aligned st store as imprecise spilled registers Date: Tue, 2 Jan 2024 11:07:26 -0800 Message-Id: <20240102190726.2017424-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable With patch set [1], precision backtracing supports register spill/fill to/from the stack. The patch [2] allows initial imprecise register spill with content 0. This is a common case for cpuv3 and lower for initializing the stack variables with pattern r1 =3D 0 *(u64 *)(r10 - 8) =3D r1 and the [2] has demonstrated good verification improvement. For cpuv4, the initialization could be *(u64 *)(r10 - 8) =3D 0 The current verifier marks the r10-8 contents with STACK_ZERO. Similar to [2], let us permit the above insn to behave like imprecise register spill which can reduce number of verified states. I checked cpuv3 and cpuv4 with and without this patch. There is no change for cpuv3 since '*(u64 *)(r10 - 8) =3D 0' is only generated with cpuv4. For cpuv4: $ ../veristat -C old.cpuv4.csv new.cpuv4.csv -e file,prog,insns,states -s= '|insns_diff|' File Program = Insns (A) Insns (B) Insns (DIFF)= States (A) States (B) States (DIFF) ----------------------------------------------------- ------------------= ---------------------------------- --------- --------- ---------------= ---------- ---------- ------------- pyperf600_bpf_loop.bpf.linked3.o on_event = 6066 4889 -1177 (-19.40%)= 403 321 -82 (-20.35%) xdp_synproxy_kern.bpf.linked3.o syncookie_tc = 12412 11719 -693 (-5.58%)= 345 330 -15 (-4.35%) xdp_synproxy_kern.bpf.linked3.o syncookie_xdp = 12478 11794 -684 (-5.48%)= 346 331 -15 (-4.34%) test_cls_redirect.bpf.linked3.o cls_redirect = 35483 35387 -96 (-0.27%)= 2179 2177 -2 (-0.09%) local_storage_bench.bpf.linked3.o get_local = 228 168 -60 (-26.32%)= 17 14 -3 (-17.65%) test_l4lb_noinline.bpf.linked3.o balancer_ingress = 4494 4522 +28 (+0.62%)= 217 219 +2 (+0.92%) test_l4lb_noinline_dynptr.bpf.linked3.o balancer_ingress = 1432 1455 +23 (+1.61%)= 92 94 +2 (+2.17%) verifier_iterating_callbacks.bpf.linked3.o widening = 52 41 -11 (-21.15%)= 4 3 -1 (-25.00%) test_xdp_noinline.bpf.linked3.o balancer_ingress_v= 6 3462 3458 -4 (-0.12%)= 216 216 +0 (+0.00%) ... test_l4lb_noinline and test_l4lb_noinline_dynptr has minor regression, bu= t pyperf600_bpf_loop and local_storage_bench gets pretty good improvement. [1] https://lore.kernel.org/all/20231205184248.1502704-1-andrii@kernel.= org/ [2] https://lore.kernel.org/all/20231205184248.1502704-9-andrii@kernel.= org/ Cc: Kuniyuki Iwashima Cc: Martin KaFai Lau Signed-off-by: Yonghong Song --- kernel/bpf/verifier.c | 2 +- tools/testing/selftests/bpf/progs/verifier_spill_fill.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a376eb609c41..17ad0228270e 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4491,7 +4491,7 @@ static int check_stack_write_fixed_off(struct bpf_v= erifier_env *env, if (fls64(reg->umax_value) > BITS_PER_BYTE * size) state->stack[spi].spilled_ptr.id =3D 0; } else if (!reg && !(off % BPF_REG_SIZE) && is_bpf_st_mem(insn) && - insn->imm !=3D 0 && env->bpf_capable) { + env->bpf_capable) { struct bpf_reg_state fake_reg =3D {}; =20 __mark_reg_known(&fake_reg, insn->imm); diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/to= ols/testing/selftests/bpf/progs/verifier_spill_fill.c index 39fe3372e0e0..05de3de56e79 100644 --- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c +++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c @@ -496,13 +496,13 @@ SEC("raw_tp") __log_level(2) __success /* make sure fp-8 is all STACK_ZERO */ -__msg("2: (7a) *(u64 *)(r10 -8) =3D 0 ; R10=3Dfp0 fp-8_w=3D0000= 0000") +__msg("2: (7a) *(u64 *)(r10 -8) =3D 0 ; R10=3Dfp0 fp-8_w=3D0") /* but fp-16 is spilled IMPRECISE zero const reg */ __msg("4: (7b) *(u64 *)(r10 -16) =3D r0 ; R0_w=3D0 R10=3Dfp0 fp-1= 6_w=3D0") /* validate that assigning R2 from STACK_ZERO doesn't mark register * precise immediately; if necessary, it will be marked precise later */ -__msg("6: (71) r2 =3D *(u8 *)(r10 -1) ; R2_w=3D0 R10=3Dfp0 fp-8= _w=3D00000000") +__msg("6: (71) r2 =3D *(u8 *)(r10 -1) ; R2_w=3D0 R10=3Dfp0 fp-8= _w=3D0") /* similarly, when R2 is assigned from spilled register, it is initially * imprecise, but will be marked precise later once it is used in precis= e context */ --=20 2.34.1