diff options
| author | Ravi Bangoria <ravi.bangoria@linux.ibm.com> | 2021-10-12 18:00:54 +0530 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2021-11-25 11:25:32 +1100 |
| commit | 9c70c7147ffec31de67d33243570a533b29f9759 (patch) | |
| tree | 7c7e32383adc9ddce499014df4dd355d49f0bf3c /arch/powerpc/net | |
| parent | 983bdc0245a29cdefcd30d9d484d3edbc4b6d787 (diff) | |
| download | lwn-9c70c7147ffec31de67d33243570a533b29f9759.tar.gz lwn-9c70c7147ffec31de67d33243570a533b29f9759.zip | |
bpf ppc64: Access only if addr is kernel address
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 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 <ast@kernel.org>
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211012123056.485795-7-hbathini@linux.ibm.com
Diffstat (limited to 'arch/powerpc/net')
| -rw-r--r-- | arch/powerpc/net/bpf_jit_comp64.c | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c index ede8cb3e453f..472d4a551945 100644 --- a/arch/powerpc/net/bpf_jit_comp64.c +++ b/arch/powerpc/net/bpf_jit_comp64.c @@ -789,6 +789,32 @@ emit_clear: /* 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 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_1], src_reg, off)); + if (IS_ENABLED(CONFIG_PPC_BOOK3E_64)) + PPC_LI64(b2p[TMP_REG_2], 0x8000000000000000ul); + else /* BOOK3S_64 */ + PPC_LI64(b2p[TMP_REG_2], PAGE_OFFSET); + 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)); + /* + * 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. + */ + 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)); |