From: Jann Horn <ja...@google.com>
32-bit ALU ops operate on 32-bit values and have 32-bit outputs.
Adjust the verifier accordingly.
Fixes: f1174f77b50c ("bpf/verifier: rework value tracking")
Signed-off-by: Jann Horn <ja...@google.com>
Signed-off-by: Alexei Starovoitov <a...@kernel.org>
---
kernel/bpf/verifier.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f716bdf29dd0..ecdc265244ca 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2017,6 +2017,10 @@ static int adjust_ptr_min_max_vals(struct
bpf_verifier_env *env,
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,
struct bpf_insn *insn,
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;
s64 smin_val, smax_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;
smax_val = src_reg.smax_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);
break;
case BPF_LSH:
- if (umax_val > 63) {
- /* Shifts greater than 63 are undefined. This includes
- * shifts by a negative number.
+ if (umax_val >= insn_bitness) {
+ /* Shifts greater than 31 or 63 are undefined.
+ * This includes shifts by a negative number.
*/
mark_reg_unknown(env, regs, insn->dst_reg);
break;
@@ -2196,9 +2196,9 @@ static int adjust_scalar_min_max_vals(struct
bpf_verifier_env *env,
__update_reg_bounds(dst_reg);
break;
case BPF_RSH:
- if (umax_val > 63) {
- /* Shifts greater than 63 are undefined. This includes
- * shifts by a negative number.
+ if (umax_val >= insn_bitness) {
+ /* Shifts greater than 31 or 63 are undefined.
+ * This includes shifts by a negative number.
*/
mark_reg_unknown(env, regs, insn->dst_reg);
break;
@@ -2234,6 +2234,12 @@ static int adjust_scalar_min_max_vals(struct
bpf_verifier_env *env,
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_bound_offset(dst_reg);
return 0;
--
2.9.5
