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([38.34.87.7]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2c9a4c0fe8dsm216693a91.0.2024.07.04.03.24.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Jul 2024 03:24:21 -0700 (PDT) From: Eduard Zingerman To: bpf@vger.kernel.org, ast@kernel.org Cc: andrii@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, kernel-team@fb.com, yonghong.song@linux.dev, puranjay@kernel.org, jose.marchesi@oracle.com, Eduard Zingerman Subject: [RFC bpf-next v2 3/9] bpf, x86, riscv, arm: no_caller_saved_registers for bpf_get_smp_processor_id() Date: Thu, 4 Jul 2024 03:23:55 -0700 Message-ID: <20240704102402.1644916-4-eddyz87@gmail.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240704102402.1644916-1-eddyz87@gmail.com> References: <20240704102402.1644916-1-eddyz87@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The function bpf_get_smp_processor_id() is processed in a different way, depending on the arch: - on x86 verifier replaces call to bpf_get_smp_processor_id() with a sequence of instructions that modify only r0; - on riscv64 jit replaces call to bpf_get_smp_processor_id() with a sequence of instructions that modify only r0; - on arm64 jit replaces call to bpf_get_smp_processor_id() with a sequence of instructions that modify only r0 and tmp registers. These rewrites satisfy attribute no_caller_saved_registers contract. Allow rewrite of no_caller_saved_registers patterns for bpf_get_smp_processor_id() in order to use this function as a canary for no_caller_saved_registers tests. Signed-off-by: Eduard Zingerman --- kernel/bpf/helpers.c | 1 + kernel/bpf/verifier.c | 11 +++++++++-- 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 229396172026..26863b162a88 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -158,6 +158,7 @@ const struct bpf_func_proto bpf_get_smp_processor_id_proto = { .func = bpf_get_smp_processor_id, .gpl_only = false, .ret_type = RET_INTEGER, + .allow_nocsr = true, }; BPF_CALL_0(bpf_get_numa_node_id) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d16a249b59ad..99115c552e3b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16029,7 +16029,14 @@ static u8 get_helper_reg_mask(const struct bpf_func_proto *fn) */ static bool verifier_inlines_helper_call(struct bpf_verifier_env *env, s32 imm) { - return false; + switch (imm) { +#ifdef CONFIG_X86_64 + case BPF_FUNC_get_smp_processor_id: + return env->prog->jit_requested && bpf_jit_supports_percpu_insn(); +#endif + default: + return false; + } } /* If 'insn' is a call that follows no_caller_saved_registers contract @@ -20703,7 +20710,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env) #ifdef CONFIG_X86_64 /* Implement bpf_get_smp_processor_id() inline. */ if (insn->imm == BPF_FUNC_get_smp_processor_id && - prog->jit_requested && bpf_jit_supports_percpu_insn()) { + verifier_inlines_helper_call(env, insn->imm)) { /* BPF_FUNC_get_smp_processor_id inlining is an * optimization, so if pcpu_hot.cpu_number is ever * changed in some incompatible and hard to support -- 2.45.2