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Subject[PATCH 4.14 074/118] bpf: arsh is not supported in 32 bit alu thus reject it
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Borkmann <daniel@iogearbox.net>

commit 7891a87efc7116590eaba57acc3c422487802c6f upstream.

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: 17a5267067f3 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/bpf/verifier.c | 5 +++
tools/testing/selftests/bpf/test_verifier.c | 40 ++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2493,6 +2493,11 @@ static int check_alu_op(struct bpf_verif
return -EINVAL;
}

+ if (opcode == BPF_ARSH && BPF_CLASS(insn->code) != BPF_ALU64) {
+ verbose("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;
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -273,6 +273,46 @@ static struct bpf_test tests[] = {
.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 = {
BPF_ALU64_REG(BPF_MOV, BPF_REG_0, BPF_REG_2),

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