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bpf: fix 32-bit ALU op verification

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32-bit ALU ops operate on 32-bit values and have 32-bit outputs.
Adjust the verifier accordingly.

Fixes: f1174f77b5 ("bpf/verifier: rework value tracking")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Jann Horn 2017-12-18 20:11:56 -08:00 committed by Daniel Borkmann
parent 0c17d1d2c6
commit 468f6eafa6
1 changed files with 17 additions and 11 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

28
kernel/bpf/verifier.c
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@ -2017,6 +2017,10 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
return 0; return 0;
} }
/* WARNING: This function does calculations on 64-bit values, but the actual
* execution may occur on 32-bit values. Therefore, things like bitshifts
* need extra checks in the 32-bit case.
*/
static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
struct bpf_insn *insn, struct bpf_insn *insn,
struct bpf_reg_state *dst_reg, struct bpf_reg_state *dst_reg,
@ -2027,12 +2031,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
bool src_known, dst_known; bool src_known, dst_known;
s64 smin_val, smax_val; s64 smin_val, smax_val;
u64 umin_val, umax_val; u64 umin_val, umax_val;
u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32;
if (BPF_CLASS(insn->code) != BPF_ALU64) {
/* 32-bit ALU ops are (32,32)->64 */
coerce_reg_to_size(dst_reg, 4);
coerce_reg_to_size(&src_reg, 4);
}
smin_val = src_reg.smin_value; smin_val = src_reg.smin_value;
smax_val = src_reg.smax_value; smax_val = src_reg.smax_value;
umin_val = src_reg.umin_value; umin_val = src_reg.umin_value;
@ -2168,9 +2168,9 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
__update_reg_bounds(dst_reg); __update_reg_bounds(dst_reg);
break; break;
case BPF_LSH: case BPF_LSH:
if (umax_val > 63) { if (umax_val >= insn_bitness) {
/* Shifts greater than 63 are undefined. This includes /* Shifts greater than 31 or 63 are undefined.
* shifts by a negative number. * This includes shifts by a negative number.
*/ */
mark_reg_unknown(env, regs, insn->dst_reg); mark_reg_unknown(env, regs, insn->dst_reg);
break; break;
@ -2196,9 +2196,9 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
__update_reg_bounds(dst_reg); __update_reg_bounds(dst_reg);
break; break;
case BPF_RSH: case BPF_RSH:
if (umax_val > 63) { if (umax_val >= insn_bitness) {
/* Shifts greater than 63 are undefined. This includes /* Shifts greater than 31 or 63 are undefined.
* shifts by a negative number. * This includes shifts by a negative number.
*/ */
mark_reg_unknown(env, regs, insn->dst_reg); mark_reg_unknown(env, regs, insn->dst_reg);
break; break;
@ -2234,6 +2234,12 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
break; break;
} }
if (BPF_CLASS(insn->code) != BPF_ALU64) {
/* 32-bit ALU ops are (32,32)->32 */
coerce_reg_to_size(dst_reg, 4);
coerce_reg_to_size(&src_reg, 4);
}
__reg_deduce_bounds(dst_reg); __reg_deduce_bounds(dst_reg);
__reg_bound_offset(dst_reg); __reg_bound_offset(dst_reg);
return 0; return 0;