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| author | Alexei Starovoitov <ast@kernel.org> | 2021-02-01 21:38:37 -0800 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-02-04 16:46:44 +0100 |
| commit | 4c5de127598e1b725aa3a5e38ac711472566ca60 (patch) | |
| tree | 0a1cdb904666323a00bb0c46c1825df2b2983750 /arch/x86/net | |
| parent | 5f10c1aac8b29d225d19a74656865d1ee3db6eaa (diff) | |
| download | linux-4c5de127598e1b725aa3a5e38ac711472566ca60.tar.gz | |
bpf: Emit explicit NULL pointer checks for PROBE_LDX instructions.
PTR_TO_BTF_ID registers contain either kernel pointer or NULL. Emit the NULL check explicitly by JIT instead of going into do_user_addr_fault() on NULL deference. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20210202053837.95909-1-alexei.starovoitov@gmail.com
Diffstat (limited to 'arch/x86/net')
| -rw-r--r-- | arch/x86/net/bpf_jit_comp.c | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index b7a2911bda77..a3dc3bd154ac 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -930,6 +930,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u32 dst_reg = insn->dst_reg; u32 src_reg = insn->src_reg; u8 b2 = 0, b3 = 0; + u8 *start_of_ldx; s64 jmp_offset; u8 jmp_cond; u8 *func; @@ -1278,12 +1279,30 @@ st: if (is_imm8(insn->off)) case BPF_LDX | BPF_PROBE_MEM | BPF_W: 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); + /* 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) */; + start_of_ldx = prog; + } emit_ldx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->off); if (BPF_MODE(insn->code) == BPF_PROBE_MEM) { struct exception_table_entry *ex; u8 *_insn = image + proglen; s64 delta; + /* populate jmp_offset for JMP above */ + start_of_ldx[-1] = prog - start_of_ldx; + if (!bpf_prog->aux->extable) break; |