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bpf: arsh is not supported in 32 bit alu thus reject it

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The following snippet was throwing an 'unknown opcode cc' warning
in BPF interpreter:

  0: (18) r0 = 0x0
  2: (7b) *(u64 *)(r10 -16) = r0
  3: (cc) (u32) r0 s>>= (u32) r0
  4: (95) exit

Although a number of JITs do support BPF_ALU | BPF_ARSH | BPF_{K,X}
generation, not all of them do and interpreter does neither. We can
leave existing ones and implement it later in bpf-next for the
remaining ones, but reject this properly in verifier for the time
being.

Fixes: 17a5267067 ("bpf: verifier (add verifier core)")
Reported-by: syzbot+93c4904c5c70348a6890@syzkaller.appspotmail.com
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2018-01-10 20:04:37 +01:00 committed by Alexei Starovoitov
parent 4095034393
commit 7891a87efc
2 changed files with 45 additions and 0 deletions
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5
kernel/bpf/verifier.c
View File

@ -2493,6 +2493,11 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
return -EINVAL;
}
if (opcode == BPF_ARSH && BPF_CLASS(insn->code) != BPF_ALU64) {
verbose(env, "BPF_ARSH not supported for 32 bit ALU\n");
return -EINVAL;
}
if ((opcode == BPF_LSH || opcode == BPF_RSH ||
opcode == BPF_ARSH) && BPF_SRC(insn->code) == BPF_K) {
int size = BPF_CLASS(insn->code) == BPF_ALU64 ? 64 : 32;

40
tools/testing/selftests/bpf/test_verifier.c
View File

@ -272,6 +272,46 @@ static struct bpf_test tests[] = {
.errstr = "invalid bpf_ld_imm64 insn",
.result = REJECT,
},
{
"arsh32 on imm",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_ALU32_IMM(BPF_ARSH, BPF_REG_0, 5),
BPF_EXIT_INSN(),
},
.result = REJECT,
.errstr = "BPF_ARSH not supported for 32 bit ALU",
},
{
"arsh32 on reg",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_MOV64_IMM(BPF_REG_1, 5),
BPF_ALU32_REG(BPF_ARSH, BPF_REG_0, BPF_REG_1),
BPF_EXIT_INSN(),
},
.result = REJECT,
.errstr = "BPF_ARSH not supported for 32 bit ALU",
},
{
"arsh64 on imm",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_ALU64_IMM(BPF_ARSH, BPF_REG_0, 5),
BPF_EXIT_INSN(),
},
.result = ACCEPT,
},
{
"arsh64 on reg",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_MOV64_IMM(BPF_REG_1, 5),
BPF_ALU64_REG(BPF_ARSH, BPF_REG_0, BPF_REG_1),
BPF_EXIT_INSN(),
},
.result = ACCEPT,
},
{
"no bpf_exit",
.insns = {