From patchwork Mon May 31 13:13:53 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 451254 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B2CFFC47080 for ; Mon, 31 May 2021 13:31:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 90C736142A for ; Mon, 31 May 2021 13:31:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232638AbhEaNd0 (ORCPT ); Mon, 31 May 2021 09:33:26 -0400 Received: from mail.kernel.org ([198.145.29.99]:39186 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232161AbhEaNbZ (ORCPT ); Mon, 31 May 2021 09:31:25 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0A25D613B6; Mon, 31 May 2021 13:23:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1622467416; bh=vRqAwUqYtFJ1JEWXTPZFIsAOh+Kh2rbyILSszCFx2fw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oeEfACIamPmDRERrZIpYbCC+/ustdhrmWCF2YRlNFZRsRpnl9cxDmrLqJLn6U8F/D rjUHToqtT8mEFc5JN6CE8xLHv6t97oa/OA5Ke8r7hUkwDgz0PuMlXWnSqMO7oZi/5w JUYxUbNwVj14v/mi9I254UNRaihGqOyUIddK2+Jc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , Piotr Krysiuk , Daniel Borkmann , Alexei Starovoitov , Ovidiu Panait Subject: [PATCH 4.19 057/116] bpf: Fix mask direction swap upon off reg sign change Date: Mon, 31 May 2021 15:13:53 +0200 Message-Id: <20210531130642.106387425@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210531130640.131924542@linuxfoundation.org> References: <20210531130640.131924542@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Daniel Borkmann commit bb01a1bba579b4b1c5566af24d95f1767859771e upstream Masking direction as indicated via mask_to_left is considered to be calculated once and then used to derive pointer limits. Thus, this needs to be placed into bpf_sanitize_info instead so we can pass it to sanitize_ptr_alu() call after the pointer move. Piotr noticed a corner case where the off reg causes masking direction change which then results in an incorrect final aux->alu_limit. Fixes: 7fedb63a8307 ("bpf: Tighten speculative pointer arithmetic mask") Reported-by: Piotr Krysiuk Signed-off-by: Daniel Borkmann Reviewed-by: Piotr Krysiuk Acked-by: Alexei Starovoitov Signed-off-by: Ovidiu Panait Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/verifier.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2738,18 +2738,10 @@ enum { }; static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, - const struct bpf_reg_state *off_reg, - u32 *alu_limit, u8 opcode) + u32 *alu_limit, bool mask_to_left) { - bool off_is_neg = off_reg->smin_value < 0; - bool mask_to_left = (opcode == BPF_ADD && off_is_neg) || - (opcode == BPF_SUB && !off_is_neg); u32 max = 0, ptr_limit = 0; - if (!tnum_is_const(off_reg->var_off) && - (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) - return REASON_BOUNDS; - switch (ptr_reg->type) { case PTR_TO_STACK: /* Offset 0 is out-of-bounds, but acceptable start for the @@ -2817,6 +2809,7 @@ static bool sanitize_needed(u8 opcode) struct bpf_sanitize_info { struct bpf_insn_aux_data aux; + bool mask_to_left; }; static int sanitize_ptr_alu(struct bpf_verifier_env *env, @@ -2848,7 +2841,16 @@ static int sanitize_ptr_alu(struct bpf_v if (vstate->speculative) goto do_sim; - err = retrieve_ptr_limit(ptr_reg, off_reg, &alu_limit, opcode); + if (!commit_window) { + if (!tnum_is_const(off_reg->var_off) && + (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) + return REASON_BOUNDS; + + info->mask_to_left = (opcode == BPF_ADD && off_is_neg) || + (opcode == BPF_SUB && !off_is_neg); + } + + err = retrieve_ptr_limit(ptr_reg, &alu_limit, info->mask_to_left); if (err < 0) return err;