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([38.34.87.7]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-7c6b6356ad2sm3598887a12.69.2024.08.16.18.51.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Aug 2024 18:51:56 -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, jose.marchesi@oracle.com, Eduard Zingerman Subject: [PATCH bpf-next v2 3/5] bpf: support bpf_fastcall patterns for kfuncs Date: Fri, 16 Aug 2024 18:51:38 -0700 Message-ID: <20240817015140.1039351-4-eddyz87@gmail.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240817015140.1039351-1-eddyz87@gmail.com> References: <20240817015140.1039351-1-eddyz87@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net Recognize bpf_fastcall patterns around kfunc calls. For example, suppose bpf_cast_to_kern_ctx() follows bpf_fastcall contract (which it does), in such a case allow verifier to rewrite BPF program below: r2 = 1; *(u64 *)(r10 - 32) = r2; call %[bpf_cast_to_kern_ctx]; r2 = *(u64 *)(r10 - 32); r0 = r2; By removing the spill/fill pair: r2 = 1; call %[bpf_cast_to_kern_ctx]; r0 = r2; Signed-off-by: Eduard Zingerman Acked-by: Yonghong Song --- kernel/bpf/verifier.c | 37 ++++++++++++++++++++++++++++++++++++- 1 file changed, 36 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b18a21bb5e6e..5dafcfff729e 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16112,7 +16112,7 @@ static int visit_func_call_insn(int t, struct bpf_insn *insns, */ static u32 helper_fastcall_clobber_mask(const struct bpf_func_proto *fn) { - u8 mask; + u32 mask; int i; mask = 0; @@ -16140,6 +16140,28 @@ static bool verifier_inlines_helper_call(struct bpf_verifier_env *env, s32 imm) } } +/* Same as helper_fastcall_clobber_mask() but for kfuncs, see comment above */ +static u32 kfunc_fastcall_clobber_mask(struct bpf_kfunc_call_arg_meta *meta) +{ + const struct btf_param *params; + u32 vlen, i, mask; + + params = btf_params(meta->func_proto); + vlen = btf_type_vlen(meta->func_proto); + mask = 0; + if (!btf_type_is_void(btf_type_by_id(meta->btf, meta->func_proto->type))) + mask |= BIT(BPF_REG_0); + for (i = 0; i < vlen; ++i) + mask |= BIT(BPF_REG_1 + i); + return mask; +} + +/* Same as verifier_inlines_helper_call() but for kfuncs, see comment above */ +static bool is_fastcall_kfunc_call(struct bpf_kfunc_call_arg_meta *meta) +{ + return false; +} + /* LLVM define a bpf_fastcall function attribute. * This attribute means that function scratches only some of * the caller saved registers defined by ABI. @@ -16237,6 +16259,19 @@ static void mark_fastcall_pattern_for_call(struct bpf_verifier_env *env, bpf_jit_inlines_helper_call(call->imm)); } + if (bpf_pseudo_kfunc_call(call)) { + struct bpf_kfunc_call_arg_meta meta; + int err; + + err = fetch_kfunc_meta(env, call, &meta, NULL); + if (err < 0) + /* error would be reported later */ + return; + + clobbered_regs_mask = kfunc_fastcall_clobber_mask(&meta); + can_be_inlined = is_fastcall_kfunc_call(&meta); + } + if (clobbered_regs_mask == ALL_CALLER_SAVED_REGS) return;