From 91b7fbf3936f5c27d1673264dc24a713290e2165 Mon Sep 17 00:00:00 2001 From: Eduard Zingerman Date: Mon, 22 Jul 2024 16:38:37 -0700 Subject: [PATCH] bpf, x86, riscv, arm: no_caller_saved_registers for bpf_get_smp_processor_id() 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 Link: https://lore.kernel.org/r/20240722233844.1406874-4-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Andrii Nakryiko --- 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 b5f0adae82933..d02ae323996ba 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 7587336967cc3..df3be12096cf2 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16130,7 +16130,14 @@ static u32 helper_nocsr_clobber_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; + } } /* GCC and LLVM define a no_caller_saved_registers function attribute. @@ -20834,7 +20841,7 @@ patch_map_ops_generic: #if defined(CONFIG_X86_64) && !defined(CONFIG_UML) /* 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 -- 2.50.1