From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E5966C433EF for ; Mon, 20 Dec 2021 14:54:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238529AbhLTOyW (ORCPT ); Mon, 20 Dec 2021 09:54:22 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:43080 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235630AbhLTOvi (ORCPT ); Mon, 20 Dec 2021 09:51:38 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 7C4BB611A7; Mon, 20 Dec 2021 14:51:38 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 61275C36AE7; Mon, 20 Dec 2021 14:51:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1640011897; bh=Plyd6OrvugmVCjWxktHb7GvXnPeTbcSkZgmym+oLiQc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YotAJxMlweNlP1JJQ8zqbVdoQALYe7aRDuZv7y3QULMxjoUo1Ba+XObPEuB9+PO5T Yi4o6V7JduHpHYLmRvxzg2zrf1oND1o88LfWnyGHqAIOyvoqZGqQAwmCZXiZc4Xnag 5uYi0yGZjVJCW3/g0PCyY+6QMHJdqbcgjXRE/qQk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Brendan Jackman , Daniel Borkmann , Alexei Starovoitov Subject: [PATCH 5.15 014/177] bpf, selftests: Add test case for atomic fetch on spilled pointer Date: Mon, 20 Dec 2021 15:32:44 +0100 Message-Id: <20211220143040.554980581@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20211220143040.058287525@linuxfoundation.org> References: <20211220143040.058287525@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Daniel Borkmann commit 180486b430f4e22cc00a478163d942804baae4b5 upstream. Test whether unprivileged would be able to leak the spilled pointer either by exporting the returned value from the atomic{32,64} operation or by reading and exporting the value from the stack after the atomic operation took place. Note that for unprivileged, the below atomic cmpxchg test case named "Dest pointer in r0 - succeed" is failing. The reason is that in the dst memory location (r10 -8) there is the spilled register r10: 0: R1=ctx(id=0,off=0,imm=0) R10=fp0 0: (bf) r0 = r10 1: R0_w=fp0 R1=ctx(id=0,off=0,imm=0) R10=fp0 1: (7b) *(u64 *)(r10 -8) = r0 2: R0_w=fp0 R1=ctx(id=0,off=0,imm=0) R10=fp0 fp-8_w=fp 2: (b7) r1 = 0 3: R0_w=fp0 R1_w=invP0 R10=fp0 fp-8_w=fp 3: (db) r0 = atomic64_cmpxchg((u64 *)(r10 -8), r0, r1) 4: R0_w=fp0 R1_w=invP0 R10=fp0 fp-8_w=mmmmmmmm 4: (79) r1 = *(u64 *)(r0 -8) 5: R0_w=fp0 R1_w=invP(id=0) R10=fp0 fp-8_w=mmmmmmmm 5: (b7) r0 = 0 6: R0_w=invP0 R1_w=invP(id=0) R10=fp0 fp-8_w=mmmmmmmm 6: (95) exit However, allowing this case for unprivileged is a bit useless given an update with a new pointer will fail anyway: 0: R1=ctx(id=0,off=0,imm=0) R10=fp0 0: (bf) r0 = r10 1: R0_w=fp0 R1=ctx(id=0,off=0,imm=0) R10=fp0 1: (7b) *(u64 *)(r10 -8) = r0 2: R0_w=fp0 R1=ctx(id=0,off=0,imm=0) R10=fp0 fp-8_w=fp 2: (db) r0 = atomic64_cmpxchg((u64 *)(r10 -8), r0, r10) R10 leaks addr into mem Acked-by: Brendan Jackman Signed-off-by: Daniel Borkmann Signed-off-by: Alexei Starovoitov [only backport one test for 5.15.y - gregkh] Signed-off-by: Greg Kroah-Hartman --- tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c | 23 ++++++++++++++++++ 1 file changed, 23 insertions(+) --- a/tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c +++ b/tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c @@ -118,4 +118,27 @@ BPF_EXIT_INSN(), }, .result = ACCEPT, + .result_unpriv = REJECT, + .errstr_unpriv = "leaking pointer from stack off -8", +}, +{ + "Dest pointer in r0 - succeed, check 2", + .insns = { + /* r0 = &val */ + BPF_MOV64_REG(BPF_REG_0, BPF_REG_10), + /* val = r0; */ + BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_0, -8), + /* r5 = &val */ + BPF_MOV64_REG(BPF_REG_5, BPF_REG_10), + /* r0 = atomic_cmpxchg(&val, r0, r5); */ + BPF_ATOMIC_OP(BPF_DW, BPF_CMPXCHG, BPF_REG_10, BPF_REG_5, -8), + /* r1 = *r0 */ + BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, -8), + /* exit(0); */ + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .result = ACCEPT, + .result_unpriv = REJECT, + .errstr_unpriv = "R5 leaks addr into mem", },