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Tue, 21 Sep 2021 13:30:33 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 18F314C046; Tue, 21 Sep 2021 13:30:29 +0000 (GMT) Received: from hbathini-workstation.ibm.com.com (unknown [9.43.117.91]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 21 Sep 2021 13:30:28 +0000 (GMT) From: Hari Bathini To: naveen.n.rao@linux.ibm.com, christophe.leroy@csgroup.eu, mpe@ellerman.id.au, ast@kernel.org, daniel@iogearbox.net Cc: 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, Hari Bathini Subject: [PATCH v3 8/8] bpf ppc32: Access only if addr is kernel address Date: Tue, 21 Sep 2021 18:59:43 +0530 Message-Id: <20210921132943.489732-9-hbathini@linux.ibm.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210921132943.489732-1-hbathini@linux.ibm.com> References: <20210921132943.489732-1-hbathini@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: eRC9qyM7YPkJN-zPFN7we_L_WNyx5pKU X-Proofpoint-GUID: WwzNd9atNVBqQYu5SbxFFQo32EHCV-XU 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=2021-09-21_01,2021-09-20_01,2020-04-07_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 mlxlogscore=999 mlxscore=0 phishscore=0 impostorscore=0 spamscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 lowpriorityscore=0 clxscore=1015 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2109030001 definitions=main-2109210083 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org 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. Though PPC32 does not support read protection, 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 is kernel address, 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: Hari Bathini --- Changes in v3: * Updated jump for PPC_BCC to always be the same while emitting a NOP instruction when needed. arch/powerpc/net/bpf_jit_comp32.c | 35 +++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c index 1239643f532c..59849e1230d2 100644 --- a/arch/powerpc/net/bpf_jit_comp32.c +++ b/arch/powerpc/net/bpf_jit_comp32.c @@ -825,6 +825,41 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context * case BPF_LDX | BPF_MEM | BPF_DW: /* dst = *(u64 *)(ul) (src + off) */ fallthrough; 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 is kernel address (see is_kernel_addr()), otherwise + * set dst_reg=0 and move on. + */ + if (BPF_MODE(code) == BPF_PROBE_MEM) { + EMIT(PPC_RAW_ADDI(b2p[TMP_REG], src_reg, off)); + PPC_LI32(_R0, TASK_SIZE); + EMIT(PPC_RAW_CMPLW(b2p[TMP_REG], _R0)); + PPC_BCC(COND_GT, (ctx->idx + 5) * 4); + EMIT(PPC_RAW_LI(dst_reg, 0)); + /* + * For BPF_DW case, "li reg_h,0" would be needed when + * !fp->aux->verifier_zext. Emit NOP otherwise. + * + * Note that "li reg_h,0" is emitted for BPF_B/H/W case, + * if necessary. So, jump there insted of emitting an + * additional "li reg_h,0" instruction. + */ + if (size == BPF_DW && !fp->aux->verifier_zext) + EMIT(PPC_RAW_LI(dst_reg_h, 0)); + else + EMIT(PPC_RAW_NOP()); + /* + * Need to jump two instructions instead of one for BPF_DW case + * as there are two load instructions for dst_reg_h & dst_reg + * respectively. + */ + if (size == BPF_DW) + PPC_JMP((ctx->idx + 3) * 4); + else + PPC_JMP((ctx->idx + 2) * 4); + } + switch (size) { case BPF_B: EMIT(PPC_RAW_LBZ(dst_reg, src_reg, off)); -- 2.31.1