From patchwork Fri Mar 29 01:01:57 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrey Ignatov X-Patchwork-Id: 1068936 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=none dis=none) header.from=fb.com Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=fb.com header.i=@fb.com header.b="Nz3pHa5f"; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 44Vk3j6D7vz9sSc for ; Fri, 29 Mar 2019 12:02:25 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728631AbfC2BCY (ORCPT ); Thu, 28 Mar 2019 21:02:24 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:54234 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728546AbfC2BCY (ORCPT ); Thu, 28 Mar 2019 21:02:24 -0400 Received: from pps.filterd (m0044010.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x2T10XdO031372 for ; Thu, 28 Mar 2019 18:02:23 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-type; s=facebook; bh=ZIFtbARInn5U7oOtlJDOorZ9TSKaJHBiP/XCbqH2ag0=; b=Nz3pHa5f8fxF40kWGV5Inecaqo0keED4eYjv4/SVDdeXfaDtXr7c9cXYv4LS+GF5zq96 V3MkRPgPop8EiuioZJiU5P9MWwJ6qhKH7RuUZUBXlT5t7XZqpp90xABpGIe0zVpeE4ib yFskQEcKAbxqg1dMQO3u7rMQE11Ke54aRW4= Received: from maileast.thefacebook.com ([199.201.65.23]) by mx0a-00082601.pphosted.com with ESMTP id 2rh76u0j8b-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-SHA384 bits=256 verify=NOT) for ; Thu, 28 Mar 2019 18:02:23 -0700 Received: from mx-out.facebook.com (2620:10d:c0a1:3::13) by mail.thefacebook.com (2620:10d:c021:18::171) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA) id 15.1.1713.5; Thu, 28 Mar 2019 18:02:21 -0700 Received: by dev082.prn2.facebook.com (Postfix, from userid 572249) id F412D37028DC; Thu, 28 Mar 2019 18:02:18 -0700 (PDT) Smtp-Origin-Hostprefix: dev From: Andrey Ignatov Smtp-Origin-Hostname: dev082.prn2.facebook.com To: CC: Andrey Ignatov , , , Smtp-Origin-Cluster: prn2c23 Subject: [PATCH bpf-next 1/2] bpf: Support variable offset stack access from helpers Date: Thu, 28 Mar 2019 18:01:57 -0700 Message-ID: X-Mailer: git-send-email 2.17.1 In-Reply-To: References: X-FB-Internal: Safe MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-03-29_01:, , signatures=0 X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Currently there is a difference in how verifier checks memory access for helper arguments for PTR_TO_MAP_VALUE and PTR_TO_STACK with regard to variable part of offset. check_map_access, that is used for PTR_TO_MAP_VALUE, can handle variable offsets just fine, so that BPF program can call a helper like this: some_helper(map_value_ptr + off, size); , where offset is unknown at load time, but is checked by program to be in a safe rage (off >= 0 && off + size < map_value_size). But it's not the case for check_stack_boundary, that is used for PTR_TO_STACK, and same code with pointer to stack is rejected by verifier: some_helper(stack_value_ptr + off, size); For example: 0: (7a) *(u64 *)(r10 -16) = 0 1: (7a) *(u64 *)(r10 -8) = 0 2: (61) r2 = *(u32 *)(r1 +0) 3: (57) r2 &= 4 4: (17) r2 -= 16 5: (0f) r2 += r10 6: (18) r1 = 0xffff888111343a80 8: (85) call bpf_map_lookup_elem#1 invalid variable stack read R2 var_off=(0xfffffffffffffff0; 0x4) Add support for variable offset access to check_stack_boundary so that if offset is checked by program to be in a safe range it's accepted by verifier. Signed-off-by: Andrey Ignatov --- kernel/bpf/verifier.c | 75 +++++++++++++++++++++++++++++++------------ 1 file changed, 54 insertions(+), 21 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7c88099c4547..b7a7a9caa82f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2157,6 +2157,29 @@ static int check_xadd(struct bpf_verifier_env *env, int insn_idx, struct bpf_ins BPF_SIZE(insn->code), BPF_WRITE, -1, true); } +static int __check_stack_boundary(struct bpf_verifier_env *env, u32 regno, + int off, int access_size, + bool zero_size_allowed) +{ + struct bpf_reg_state *reg = reg_state(env, regno); + + if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 || + access_size < 0 || (access_size == 0 && !zero_size_allowed)) { + if (tnum_is_const(reg->var_off)) { + verbose(env, "invalid stack type R%d off=%d access_size=%d\n", + regno, off, access_size); + } else { + char tn_buf[48]; + + tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off); + verbose(env, "invalid stack type R%d var_off=%s access_size=%d\n", + regno, tn_buf, access_size); + } + return -EACCES; + } + return 0; +} + /* when register 'regno' is passed into function that will read 'access_size' * bytes from that pointer, make sure that it's within stack boundary * and all elements of stack are initialized. @@ -2169,7 +2192,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno, { struct bpf_reg_state *reg = reg_state(env, regno); struct bpf_func_state *state = func(env, reg); - int off, i, slot, spi; + int err, min_off, max_off, i, slot, spi; if (reg->type != PTR_TO_STACK) { /* Allow zero-byte read from NULL, regardless of pointer type */ @@ -2183,21 +2206,23 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno, return -EACCES; } - /* Only allow fixed-offset stack reads */ - if (!tnum_is_const(reg->var_off)) { - char tn_buf[48]; - - tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off); - verbose(env, "invalid variable stack read R%d var_off=%s\n", - regno, tn_buf); - return -EACCES; - } - off = reg->off + reg->var_off.value; - if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 || - access_size < 0 || (access_size == 0 && !zero_size_allowed)) { - verbose(env, "invalid stack type R%d off=%d access_size=%d\n", - regno, off, access_size); - return -EACCES; + if (tnum_is_const(reg->var_off)) { + min_off = max_off = reg->var_off.value + reg->off; + err = __check_stack_boundary(env, regno, min_off, access_size, + zero_size_allowed); + if (err) + return err; + } else { + min_off = reg->smin_value + reg->off; + max_off = reg->umax_value + reg->off; + err = __check_stack_boundary(env, regno, min_off, access_size, + zero_size_allowed); + if (err) + return err; + err = __check_stack_boundary(env, regno, max_off, access_size, + zero_size_allowed); + if (err) + return err; } if (meta && meta->raw_mode) { @@ -2206,10 +2231,10 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno, return 0; } - for (i = 0; i < access_size; i++) { + for (i = min_off; i < max_off + access_size; i++) { u8 *stype; - slot = -(off + i) - 1; + slot = -i - 1; spi = slot / BPF_REG_SIZE; if (state->allocated_stack <= slot) goto err; @@ -2222,8 +2247,16 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno, goto mark; } err: - verbose(env, "invalid indirect read from stack off %d+%d size %d\n", - off, i, access_size); + if (tnum_is_const(reg->var_off)) { + verbose(env, "invalid indirect read from stack off %d+%d size %d\n", + min_off, i - min_off, access_size); + } else { + char tn_buf[48]; + + tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off); + verbose(env, "invalid indirect read from stack var_off %s+%d size %d\n", + tn_buf, i - min_off, access_size); + } return -EACCES; mark: /* reading any byte out of 8-byte 'spill_slot' will cause @@ -2232,7 +2265,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno, mark_reg_read(env, &state->stack[spi].spilled_ptr, state->stack[spi].spilled_ptr.parent); } - return update_stack_depth(env, state, off); + return update_stack_depth(env, state, min_off); } static int check_helper_mem_access(struct bpf_verifier_env *env, int regno,