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Fri, 17 Sep 2021 15:27:33 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BA9D811C06F; Fri, 17 Sep 2021 15:32:11 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 46C2111C073; Fri, 17 Sep 2021 15:32:06 +0000 (GMT) Received: from hbathini-workstation.ibm.com (unknown [9.43.59.213]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 17 Sep 2021 15:32:06 +0000 (GMT) From: Hari Bathini To: naveen.n.rao@linux.ibm.com, mpe@ellerman.id.au, ast@kernel.org, daniel@iogearbox.net Cc: christophe.leroy@csgroup.eu, paulus@samba.org, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Ravi Bangoria , Hari Bathini Subject: [PATCH v2 6/8] bpf ppc64: Add addr > TASK_SIZE_MAX explicit check Date: Fri, 17 Sep 2021 21:00:45 +0530 Message-Id: <20210917153047.177141-7-hbathini@linux.ibm.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210917153047.177141-1-hbathini@linux.ibm.com> References: <20210917153047.177141-1-hbathini@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 0OKm82m2Ph6ZTzxupYDbVD0TrPLSXDb2 X-Proofpoint-GUID: MjrNwgkWnA_hjUYk8c0W-83_HaJwsIhA X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.182.1,Aquarius:18.0.790,Hydra:6.0.391,FMLib:17.0.607.475 definitions=2021-09-17_06,2021-09-17_02,2020-04-07_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 spamscore=0 malwarescore=0 adultscore=0 suspectscore=0 clxscore=1015 lowpriorityscore=0 priorityscore=1501 mlxlogscore=999 mlxscore=0 bulkscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2109030001 definitions=main-2109170096 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net From: Ravi Bangoria On PPC64 with KUAP enabled, any kernel code which wants to access userspace needs to be surrounded by disable-enable KUAP. But that is not happening for BPF_PROBE_MEM load instruction. So, when BPF program tries to access invalid userspace address, page-fault handler considers it as bad KUAP fault: Kernel attempted to read user page (d0000000) - exploit attempt? (uid: 0) Considering the fact that PTR_TO_BTF_ID (which uses BPF_PROBE_MEM mode) could either be a valid kernel pointer or NULL but should never be a pointer to userspace address, execute BPF_PROBE_MEM load only if addr > TASK_SIZE_MAX, otherwise set dst_reg=0 and move on. This will catch NULL, valid or invalid userspace pointers. Only bad kernel pointer will be handled by BPF exception table. [Alexei suggested for x86] Suggested-by: Alexei Starovoitov Signed-off-by: Ravi Bangoria Signed-off-by: Hari Bathini --- Changes in v2: * Refactored the code based on Christophe's comments. arch/powerpc/net/bpf_jit_comp64.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c index 2fc10995f243..eb28dbc67151 100644 --- a/arch/powerpc/net/bpf_jit_comp64.c +++ b/arch/powerpc/net/bpf_jit_comp64.c @@ -769,6 +769,29 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context * /* dst = *(u64 *)(ul) (src + off) */ case BPF_LDX | BPF_MEM | BPF_DW: case BPF_LDX | BPF_PROBE_MEM | BPF_DW: + /* + * As PTR_TO_BTF_ID that uses BPF_PROBE_MEM mode could either be a valid + * kernel pointer or NULL but not a userspace address, execute BPF_PROBE_MEM + * load only if addr > TASK_SIZE_MAX, otherwise set dst_reg=0 and move on. + */ + if (BPF_MODE(code) == BPF_PROBE_MEM) { + unsigned int adjusted_idx; + + /* + * Check if 'off' is word aligned because PPC_BPF_LL() + * (BPF_DW case) generates two instructions if 'off' is not + * word-aligned and one instruction otherwise. + */ + adjusted_idx = ((BPF_SIZE(code) == BPF_DW) && (off & 3)) ? 1 : 0; + + EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], src_reg, off)); + PPC_LI64(b2p[TMP_REG_2], TASK_SIZE_MAX); + EMIT(PPC_RAW_CMPLD(b2p[TMP_REG_1], b2p[TMP_REG_2])); + PPC_BCC(COND_GT, (ctx->idx + 4) * 4); + EMIT(PPC_RAW_LI(dst_reg, 0)); + PPC_JMP((ctx->idx + 2 + adjusted_idx) * 4); + } + switch (size) { case BPF_B: EMIT(PPC_RAW_LBZ(dst_reg, src_reg, off));