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Mon, 02 Nov 2026 04:37:28 -0800 (PST) Received: from [127.0.1.1] ([23.254.208.9]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-36a428c17bdsm36326095eec.6.2026.11.02.04.37.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Nov 2026 04:37:28 -0800 (PST) From: Qiliang Yuan Date: Mon, 02 Nov 2026 07:37:04 -0500 Subject: [PATCH bpf-next 4/5] selftests/bpf: Cover a nospec jump that becomes a nop X-Mailing-List: linux-kernel@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 Message-Id: <20261102-bpf-blind-nops-fixes-v1-4-844300e42cdb@gmail.com> References: <20261102-bpf-blind-nops-fixes-v1-0-844300e42cdb@gmail.com> In-Reply-To: <20261102-bpf-blind-nops-fixes-v1-0-844300e42cdb@gmail.com> To: Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , Luis Gerhorst , Henriette Herzog , Anton Protopopov , Xu Kuohai , Hengqi Chen , Shuah Khan Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Qiliang Yuan X-Mailer: b4 0.13.0 A conditional jump that is unsafe on a mispredicted path gets a barrier, even when it later becomes a 'goto' over dead code only. No test has such a jump, so nothing checks that bpf_opt_remove_nops() keeps it with its barrier. Compare a pointer on the mispredicted path at a jump that always goes over dead code, and check that the barrier and the jump stay for a prog loaded without CAP_PERFMON. Reported-by: Alexei Starovoitov Closes: https://lore.kernel.org/bpf/DMKHZS5B5CNO.186F6YH1T6YU4@gmail.com/ Signed-off-by: Qiliang Yuan --- .../testing/selftests/bpf/progs/verifier_unpriv.c | 35 ++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/verifier_unpriv.c b/tools/testing/selftests/bpf/progs/verifier_unpriv.c index a54b5a58b945b..b9d96366e656d 100644 --- a/tools/testing/selftests/bpf/progs/verifier_unpriv.c +++ b/tools/testing/selftests/bpf/progs/verifier_unpriv.c @@ -1072,4 +1072,39 @@ __naked void nospec_backward_call(void) " ::: __clobber_all); } +/* + * Compare a pointer at l0 on the mispredicted path, so that the jump gets a + * barrier. On the real path r1 is 0, and the jump only goes over dead code and + * becomes a nop. Keep it with its barrier. + */ +SEC("socket") +__description("unpriv: nospec on a jump that becomes a nop") +__success __success_unpriv +__caps_unpriv(CAP_BPF) +__retval(0) +#ifdef SPEC_V1 +__xlated_unpriv("r1 = 0") +__xlated_unpriv("nospec") +__xlated_unpriv("goto pc+0") +__xlated_unpriv("r0 = 0") +__xlated_unpriv("exit") +#endif +__naked void nospec_jump_becomes_nop(void) +{ + asm volatile (" \ + call %[bpf_get_prandom_u32]; \ + r0 &= 0xff; \ + r1 = 0; \ + if r0 < 0x100 goto l0_%=; \ + /* executed only speculatively */ \ + r1 = r10; \ +l0_%=: if r1 == 0 goto l1_%=; \ + r0 = 1; \ +l1_%=: r0 = 0; \ + exit; \ +" : + : __imm(bpf_get_prandom_u32) + : __clobber_all); +} + char _license[] SEC("license") = "GPL"; -- 2.43.0