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Wed, 29 Sep 2021 11:19:42 +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 v4 8/8] bpf ppc32: Access only if addr is kernel address Date: Wed, 29 Sep 2021 16:48:55 +0530 Message-Id: <20210929111855.50254-9-hbathini@linux.ibm.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210929111855.50254-1-hbathini@linux.ibm.com> References: <20210929111855.50254-1-hbathini@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 0r5rBPmu5aLXQxKkUK8bV1NpmjCe6INr X-Proofpoint-ORIG-GUID: pGdPj2uMhdqx_HZhWITf2bGg7EIsb0PY 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=2021-09-29_04,2021-09-29_01,2020-04-07_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 mlxscore=0 malwarescore=0 mlxlogscore=999 lowpriorityscore=0 spamscore=0 adultscore=0 bulkscore=0 clxscore=1015 impostorscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2109230001 definitions=main-2109290068 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net 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 Reviewed-by: Christophe Leroy --- Changes in v4: * Adjusted the emit code to avoid using temporary reg. arch/powerpc/net/bpf_jit_comp32.c | 34 +++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c index 6ee13a09c70d..2ac81563c78d 100644 --- a/arch/powerpc/net/bpf_jit_comp32.c +++ b/arch/powerpc/net/bpf_jit_comp32.c @@ -818,6 +818,40 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context * case BPF_LDX | BPF_PROBE_MEM | BPF_W: case BPF_LDX | BPF_MEM | BPF_DW: /* dst = *(u64 *)(ul) (src + off) */ 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) { + PPC_LI32(_R0, TASK_SIZE - off); + EMIT(PPC_RAW_CMPLW(src_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));