diff options
| author | Alexei Starovoitov <ast@kernel.org> | 2021-12-14 19:25:13 -0800 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-12-16 21:41:04 +0100 |
| commit | 588a25e92458c6efeb7a261d5ca5726f5de89184 (patch) | |
| tree | f1cc569bf341ba9c79283cff213b5e3beb5762f8 /arch/x86 | |
| parent | 433956e91200734d09958673a56df02d00a917c2 (diff) | |
bpf: Fix extable address check.
The verifier checks that PTR_TO_BTF_ID pointer is either valid or NULL,
but it cannot distinguish IS_ERR pointer from valid one.
When offset is added to IS_ERR pointer it may become small positive
value which is a user address that is not handled by extable logic
and has to be checked for at the runtime.
Tighten BPF_PROBE_MEM pointer check code to prevent this case.
Fixes: 4c5de127598e ("bpf: Emit explicit NULL pointer checks for PROBE_LDX instructions.")
Reported-by: Lorenzo Fontana <lorenzo.fontana@elastic.co>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/net/bpf_jit_comp.c | 49 |
1 files changed, 42 insertions, 7 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index fa58681db45e..bafe36e69227 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1252,19 +1252,54 @@ st: if (is_imm8(insn->off)) case BPF_LDX | BPF_MEM | BPF_DW: case BPF_LDX | BPF_PROBE_MEM | BPF_DW: if (BPF_MODE(insn->code) == BPF_PROBE_MEM) { - /* test src_reg, src_reg */ - maybe_emit_mod(&prog, src_reg, src_reg, true); /* always 1 byte */ - EMIT2(0x85, add_2reg(0xC0, src_reg, src_reg)); - /* jne start_of_ldx */ - EMIT2(X86_JNE, 0); + /* Though the verifier prevents negative insn->off in BPF_PROBE_MEM + * add abs(insn->off) to the limit to make sure that negative + * offset won't be an issue. + * insn->off is s16, so it won't affect valid pointers. + */ + u64 limit = TASK_SIZE_MAX + PAGE_SIZE + abs(insn->off); + u8 *end_of_jmp1, *end_of_jmp2; + + /* Conservatively check that src_reg + insn->off is a kernel address: + * 1. src_reg + insn->off >= limit + * 2. src_reg + insn->off doesn't become small positive. + * Cannot do src_reg + insn->off >= limit in one branch, + * since it needs two spare registers, but JIT has only one. + */ + + /* movabsq r11, limit */ + EMIT2(add_1mod(0x48, AUX_REG), add_1reg(0xB8, AUX_REG)); + EMIT((u32)limit, 4); + EMIT(limit >> 32, 4); + /* cmp src_reg, r11 */ + maybe_emit_mod(&prog, src_reg, AUX_REG, true); + EMIT2(0x39, add_2reg(0xC0, src_reg, AUX_REG)); + /* if unsigned '<' goto end_of_jmp2 */ + EMIT2(X86_JB, 0); + end_of_jmp1 = prog; + + /* mov r11, src_reg */ + emit_mov_reg(&prog, true, AUX_REG, src_reg); + /* add r11, insn->off */ + maybe_emit_1mod(&prog, AUX_REG, true); + EMIT2_off32(0x81, add_1reg(0xC0, AUX_REG), insn->off); + /* jmp if not carry to start_of_ldx + * Otherwise ERR_PTR(-EINVAL) + 128 will be the user addr + * that has to be rejected. + */ + EMIT2(0x73 /* JNC */, 0); + end_of_jmp2 = prog; + /* xor dst_reg, dst_reg */ emit_mov_imm32(&prog, false, dst_reg, 0); /* jmp byte_after_ldx */ EMIT2(0xEB, 0); - /* populate jmp_offset for JNE above */ - temp[4] = prog - temp - 5 /* sizeof(test + jne) */; + /* populate jmp_offset for JB above to jump to xor dst_reg */ + end_of_jmp1[-1] = end_of_jmp2 - end_of_jmp1; + /* populate jmp_offset for JNC above to jump to start_of_ldx */ start_of_ldx = prog; + end_of_jmp2[-1] = start_of_ldx - end_of_jmp2; } emit_ldx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->off); if (BPF_MODE(insn->code) == BPF_PROBE_MEM) { |