From patchwork Tue Aug 13 17:10:18 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Naveen N. 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 13 Aug 2019 18:10:41 +0100 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x7DHAeM240304730 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 13 Aug 2019 17:10:40 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7C435A404D; Tue, 13 Aug 2019 17:10:40 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9251FA405B; Tue, 13 Aug 2019 17:10:38 +0000 (GMT) Received: from naverao1-tp.ibmuc.com (unknown [9.85.107.69]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 13 Aug 2019 17:10:38 +0000 (GMT) From: "Naveen N. Rao" To: Alexei Starovoitov , Daniel Borkmann , Jiong Wang Cc: Michael Ellerman , , , , Subject: [RFC PATCH] bpf: handle 32-bit zext during constant blinding Date: Tue, 13 Aug 2019 22:40:18 +0530 X-Mailer: git-send-email 2.22.0 MIME-Version: 1.0 X-TM-AS-GCONF: 00 x-cbid: 19081317-4275-0000-0000-000003589A30 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19081317-4276-0000-0000-0000386AAAB6 Message-Id: <20190813171018.28221-1-naveen.n.rao@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-08-13_06:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=821 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908130164 Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Since BPF constant blinding is performed after the verifier pass, there are certain ALU32 instructions inserted which don't have a corresponding zext instruction inserted after. This is causing a kernel oops on powerpc and can be reproduced by running 'test_cgroup_storage' with bpf_jit_harden=2. Fix this by emitting BPF_ZEXT during constant blinding if prog->aux->verifier_zext is set. Fixes: a4b1d3c1ddf6cb ("bpf: verifier: insert zero extension according to analysis result") Reported-by: Michael Ellerman Signed-off-by: Naveen N. Rao --- This approach (the location where zext is being introduced below, in particular) works for powerpc, but I am not entirely sure if this is sufficient for other architectures as well. This is broken on v5.3-rc4. - Naveen kernel/bpf/core.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 8191a7db2777..d84146e6fd9e 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -890,7 +890,8 @@ int bpf_jit_get_func_addr(const struct bpf_prog *prog, static int bpf_jit_blind_insn(const struct bpf_insn *from, const struct bpf_insn *aux, - struct bpf_insn *to_buff) + struct bpf_insn *to_buff, + bool emit_zext) { struct bpf_insn *to = to_buff; u32 imm_rnd = get_random_int(); @@ -939,6 +940,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from, *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm); *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); *to++ = BPF_ALU32_REG(from->code, from->dst_reg, BPF_REG_AX); + if (emit_zext) + *to++ = BPF_ZEXT_REG(from->dst_reg); break; case BPF_ALU64 | BPF_ADD | BPF_K: @@ -992,6 +995,10 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from, off -= 2; *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm); *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); + if (emit_zext) { + *to++ = BPF_ZEXT_REG(BPF_REG_AX); + off--; + } *to++ = BPF_JMP32_REG(from->code, from->dst_reg, BPF_REG_AX, off); break; @@ -1005,6 +1012,8 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from, case 0: /* Part 2 of BPF_LD | BPF_IMM | BPF_DW. */ *to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ aux[0].imm); *to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd); + if (emit_zext) + *to++ = BPF_ZEXT_REG(BPF_REG_AX); *to++ = BPF_ALU64_REG(BPF_OR, aux[0].dst_reg, BPF_REG_AX); break; @@ -1088,7 +1097,8 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog) insn[1].code == 0) memcpy(aux, insn, sizeof(aux)); - rewritten = bpf_jit_blind_insn(insn, aux, insn_buff); + rewritten = bpf_jit_blind_insn(insn, aux, insn_buff, + clone->aux->verifier_zext); if (!rewritten) continue;