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Thu, 22 Oct 2026 05:05:00 -0700 (PDT) Received: from localhost ([2a03:2880:30ff:8::]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8b130073596sm25519317b3.11.2026.10.22.05.04.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Oct 2026 05:05:00 -0700 (PDT) From: Mykyta Yatsenko Subject: [PATCH bpf-next v2 0/2] bpf: Fix x86 JIT stopping before jumps converge Date: Thu, 22 Oct 2026 05:04:54 -0700 Message-Id: <20261022-jit_size_fix-v2-0-4bee6921b218@meta.com> X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-B4-Tracking: v=1; b=H4sIAOb72WoC/23NSwqDMBRG4a2Ef2yKiUXUUfdRRGJyU2/BB0mQt OLeC447PvCdA5ECU0QnDgTaOfK6oBO6ELCTWV4k2aET0KWuVamVfHMaIn9p8JylM5Wqx8bdW21 RCGyBPOeLe2LcvFwoJ/SFwMQxreFzfXZ19f/krmQpx6b1rtLWeFc/ZkrmZtcZ/XmeP8NWywKxA AAA X-Change-ID: 20261021-jit_size_fix-da316b8d492c To: bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, kernel-team@meta.com, eddyz87@gmail.com, memxor@gmail.com Cc: Mykyta Yatsenko X-Mailer: b4 0.16-dev X-Developer-Signature: v=1; a=ed25519-sha256; t=1792670698; l=1643; i=yatsenko@meta.com; s=20260324; h=from:subject:message-id; bh=heTurfQcR1GwW8nEI64/AfElAhckC7B7x6r1aELGaAQ=; b=0ijA3L0UgekmaLQiaquPBnEOcRfpXOpkaNdEkMpVV/nyb0TirulPC0MRDCHG5TfL7yi8vffeV 8GemmhOQZRQCnKpdbdi0AlLK00uMNd0VMGSMWO4Y5q1C0FaowlFlkQp X-Developer-Key: i=yatsenko@meta.com; a=ed25519; pk=1zCUBXUa66KmzfjNsG8YNlMj2ckPdqBPvFq2ww3/YaA= The x86 JIT stops its sizing passes once two passes give the same image length. A backward jump can grow while other jumps shrink, so the length may repeat with jump sizes still changing. The final pass then emits code of a different size than was sized, hits "bpf_jit: fatal error" and the program fails to load with -ENOTSUPP. Patch 1 sizes backward jumps by the insns they jump over, so no insn grows between passes and a repeated length means nothing moved. Patch 2 adds a selftest which fails to load without the fix. This was hit in CI by cgroup_tcp_skb with the unpublished branch inversion series, whose layout change happened to trigger it. Signed-off-by: Mykyta Yatsenko --- Changes in v2: - Size backward jumps by the insns they jump over instead of checking for moved insns, drop the ja -1 special case and the imm8 limit of 123 (Alexei) - Start every insn at BPF_MAX_INSN_SIZE, so none grows in the first pass - Check that the selftest program is JITed - Link to v1: https://patch.msgid.link/20261021-jit_size_fix-v1-0-b89fd32cafd6@meta.com --- Mykyta Yatsenko (2): bpf: Size backward jumps by the insns they jump over selftests/bpf: Test JIT jumps which change at a repeated image length arch/x86/net/bpf_jit_comp.c | 109 ++++++--------------- tools/testing/selftests/bpf/prog_tests/jit_insns.c | 59 +++++++++++ 2 files changed, 90 insertions(+), 78 deletions(-) --- base-commit: 65953903cd7bce4c4392ad6ab629cba78f24644e change-id: 20261021-jit_size_fix-da316b8d492c Best regards, -- Mykyta Yatsenko