| Message ID | 20210917153047.177141-7-hbathini@linux.ibm.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | bpf powerpc: Add BPF_PROBE_MEM support in powerpc JIT compiler | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
| bpf/vmtest-bpf | success | VM_Test |
| bpf/vmtest-bpf-PR | success | PR summary |
| bpf/vmtest-bpf-next-PR | success | PR summary |
| bpf/vmtest-bpf-next | success | VM_Test |
Le 17/09/2021 à 17:30, Hari Bathini a écrit : > From: Ravi Bangoria <ravi.bangoria@linux.ibm.com> > > 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. You should do like copy_from_kernel_nofault_allowed() and use the same criterias as is_kernel_addr() instead of using TASK_SIZE_MAX. > > 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 <ast@kernel.org> > Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com> > Signed-off-by: Hari Bathini <hbathini@linux.ibm.com> > --- > > 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; No need of ( ) around 'BPF_SIZE(code) == BPF_DW' > + > + 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); I think it would be more explicit if you drop adjusted_idx and do : if (BPF_SIZE(code) == BPF_DW) && (off & 3) 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)); >
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));