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[219.74.209.211]) by smtp.gmail.com with ESMTPSA id m3-20020a638c03000000b0055c02b8688asm8555583pgd.20.2023.08.14.06.42.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Aug 2023 06:42:25 -0700 (PDT) From: Leon Hwang To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, x86@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mykolal@fb.com, shuah@kernel.org, davem@davemloft.net, dsahern@kernel.org, hffilwlqm@gmail.com, tangyeechou@gmail.com, kernel-patches-bot@fb.com, maciej.fijalkowski@intel.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [RFC PATCH bpf-next 1/2] bpf, x64: Fix tailcall infinite loop bug Date: Mon, 14 Aug 2023 21:41:46 +0800 Message-ID: <20230814134147.70289-2-hffilwlqm@gmail.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230814134147.70289-1-hffilwlqm@gmail.com> References: <20230814134147.70289-1-hffilwlqm@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,HK_RANDOM_ENVFROM, HK_RANDOM_FROM,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net X-Patchwork-Delegate: bpf@iogearbox.net X-Patchwork-State: RFC From commit ebf7d1f508a73871 ("bpf, x64: rework pro/epilogue and tailcall handling in JIT"), the tailcall on x64 works better than before. From commit e411901c0b775a3a ("bpf: allow for tailcalls in BPF subprograms for x64 JIT"), tailcall is able to run in BPF subprograms on x64. From commit 5b92a28aae4dd0f8 ("bpf: Support attaching tracing BPF program to other BPF programs"), BPF program is able to trace other BPF programs. How about combining them all together? 1. FENTRY/FEXIT on a BPF subprogram. 2. A tailcall runs in the BPF subprogram. 3. The tailcall calls itself. As a result, a tailcall infinite loop comes up. And the loop halts the machine. As we know, in tail call context, the tail_call_cnt propagates by stack and RAX register between BPF subprograms. So do it in FENTRY/FEXIT trampolines. Fixes: ebf7d1f508a7 ("bpf, x64: rework pro/epilogue and tailcall handling in JIT") Fixes: e411901c0b77 ("bpf: allow for tailcalls in BPF subprograms for x64 JIT") Signed-off-by: Leon Hwang --- arch/x86/net/bpf_jit_comp.c | 23 +++++++++++++++++++---- include/linux/bpf.h | 6 ++++++ kernel/bpf/trampoline.c | 5 +++-- kernel/bpf/verifier.c | 9 +++++++-- 4 files changed, 35 insertions(+), 8 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index a5930042139d3..ca5366d97ad04 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1018,6 +1018,10 @@ static void emit_shiftx(u8 **pprog, u32 dst_reg, u8 src_reg, bool is64, u8 op) #define INSN_SZ_DIFF (((addrs[i] - addrs[i - 1]) - (prog - temp))) +/* mov rax, qword ptr [rbp - rounded_stack_depth - 8] */ +#define RESTORE_TAIL_CALL_CNT(stack) \ + EMIT3_off32(0x48, 0x8B, 0x85, -round_up(stack, 8) - 8) + static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image, int oldproglen, struct jit_context *ctx, bool jmp_padding) { @@ -1623,9 +1627,7 @@ st: if (is_imm8(insn->off)) func = (u8 *) __bpf_call_base + imm32; if (tail_call_reachable) { - /* mov rax, qword ptr [rbp - rounded_stack_depth - 8] */ - EMIT3_off32(0x48, 0x8B, 0x85, - -round_up(bpf_prog->aux->stack_depth, 8) - 8); + RESTORE_TAIL_CALL_CNT(bpf_prog->aux->stack_depth); if (!imm32) return -EINVAL; offs = 7 + x86_call_depth_emit_accounting(&prog, func); @@ -2464,6 +2466,8 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i else /* sub rsp, stack_size */ EMIT4(0x48, 0x83, 0xEC, stack_size); + if (flags & BPF_TRAMP_F_TAIL_CALL_CTX) + EMIT1(0x50); /* push rax */ /* mov QWORD PTR [rbp - rbx_off], rbx */ emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_6, -rbx_off); @@ -2516,6 +2520,12 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i restore_regs(m, &prog, regs_off); save_args(m, &prog, arg_stack_off, true); + if (flags & BPF_TRAMP_F_TAIL_CALL_CTX) + /* Before calling the original function, restore the + * tail_call_cnt from stack. + */ + RESTORE_TAIL_CALL_CNT(stack_size); + if (flags & BPF_TRAMP_F_ORIG_STACK) { emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, 8); EMIT2(0xff, 0xd0); /* call *rax */ @@ -2569,7 +2579,12 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i ret = -EINVAL; goto cleanup; } - } + } else if (flags & BPF_TRAMP_F_TAIL_CALL_CTX) + /* Before running the original function, restore the + * tail_call_cnt from stack. + */ + RESTORE_TAIL_CALL_CNT(stack_size); + /* restore return value of orig_call or fentry prog back into RAX */ if (save_ret) emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, -8); diff --git a/include/linux/bpf.h b/include/linux/bpf.h index cfabbcf47bdb8..55c72086034ef 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1028,6 +1028,11 @@ struct btf_func_model { */ #define BPF_TRAMP_F_SHARE_IPMODIFY BIT(6) +/* Indicate that current trampoline is in a tail call context. Then, it has to + * cache and restore tail_call_cnt to avoid infinite tail call loop. + */ +#define BPF_TRAMP_F_TAIL_CALL_CTX BIT(7) + /* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50 * bytes on x86. */ @@ -1147,6 +1152,7 @@ struct bpf_attach_target_info { struct module *tgt_mod; const char *tgt_name; const struct btf_type *tgt_type; + bool tail_call_ctx; }; #define BPF_DISPATCHER_MAX 48 /* Fits in 2048B */ diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 78acf28d48732..0fae334e3f7b8 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -415,8 +415,8 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut goto out; } - /* clear all bits except SHARE_IPMODIFY */ - tr->flags &= BPF_TRAMP_F_SHARE_IPMODIFY; + /* clear all bits except SHARE_IPMODIFY and TAIL_CALL_CTX */ + tr->flags &= (BPF_TRAMP_F_SHARE_IPMODIFY | BPF_TRAMP_F_TAIL_CALL_CTX); if (tlinks[BPF_TRAMP_FEXIT].nr_links || tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links) { @@ -783,6 +783,7 @@ struct bpf_trampoline *bpf_trampoline_get(u64 key, memcpy(&tr->func.model, &tgt_info->fmodel, sizeof(tgt_info->fmodel)); tr->func.addr = (void *)tgt_info->tgt_addr; + tr->flags = (tgt_info->tail_call_ctx ? BPF_TRAMP_F_TAIL_CALL_CTX : 0); out: mutex_unlock(&tr->mutex); return tr; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 4ccca1f6c9981..a78e5a2ae5c72 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -19400,10 +19400,15 @@ int bpf_check_attach_target(struct bpf_verifier_log *log, return -EINVAL; fallthrough; case BPF_MODIFY_RETURN: - case BPF_LSM_MAC: - case BPF_LSM_CGROUP: case BPF_TRACE_FENTRY: case BPF_TRACE_FEXIT: + if (tgt_prog && subprog > 0 && + tgt_prog->aux->func[subprog]->is_func && + tgt_prog->aux->tail_call_reachable) + tgt_info->tail_call_ctx = true; + fallthrough; + case BPF_LSM_MAC: + case BPF_LSM_CGROUP: if (!btf_type_is_func(t)) { bpf_log(log, "attach_btf_id %u is not a function\n", btf_id);