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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
This commit is contained in:
Alexei Starovoitov 2021-02-01 21:38:37 -08:00 committed by Daniel Borkmann
parent 5f10c1aac8
commit 4c5de12759
1 changed files with 19 additions and 0 deletions
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19
arch/x86/net/bpf_jit_comp.c
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@ -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;