Range propagation must not affect subreg_def marks, otherwise the
following example is rewritten by verifier incorrectly when
BPF_F_TEST_RND_HI32 flag is set:
0: call bpf_ktime_get_ns call bpf_ktime_get_ns
1: r0 &= 0x7fffffff after verifier r0 &= 0x7fffffff
2: w1 = w0 rewrites w1 = w0
3: if w0 < 10 goto +0 --------------> r11 = 0x2f5674a6 (r)
4: r1 >>= 32 r11 <<= 32 (r)
5: r0 = r1 r1 |= r11 (r)
6: exit; if w0 < 0xa goto pc+0
r1 >>= 32
r0 = r1
exit
(or zero extension of w1 at (2) is missing for architectures that
require zero extension for upper register half).
The following happens w/o this patch:
- r0 is marked as not a subreg at (0);
- w1 is marked as subreg at (2);
- w1 subreg_def is overridden at (3) by copy_register_state();
- w1 is read at (5) but mark_insn_zext() does not mark (2)
for zero extension, because w1 subreg_def is not set;
- because of BPF_F_TEST_RND_HI32 flag verifier inserts random
value for hi32 bits of (2) (marked (r));
- this random value is read at (5).
Reported-by: Lonial Con <kongln9170@xxxxxxxxx>
Closes: https://lore.kernel.org/bpf/7e2aa30a62d740db182c170fdd8f81c596df280d.camel@xxxxxxxxx/
Signed-off-by: Lonial Con <kongln9170@xxxxxxxxx>
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
kernel/bpf/verifier.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index dd86282ccaa4..1aa0c6360a55 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -15326,8 +15326,12 @@ static void sync_linked_regs(struct bpf_verifier_state *vstate, struct bpf_reg_s
continue;
if ((!(reg->id & BPF_ADD_CONST) && !(known_reg->id & BPF_ADD_CONST)) ||
reg->off == known_reg->off) {
+ s32 saved_subreg_def = reg->subreg_def;
+
copy_register_state(reg, known_reg);
+ reg->subreg_def = saved_subreg_def;
} else {
+ s32 saved_subreg_def = reg->subreg_def;
s32 saved_off = reg->off;
fake_reg.type = SCALAR_VALUE;
@@ -15340,6 +15344,7 @@ static void sync_linked_regs(struct bpf_verifier_state *vstate, struct bpf_reg_s
* otherwise another sync_linked_regs() will be incorrect.
*/
reg->off = saved_off;
+ reg->subreg_def = saved_subreg_def;
scalar32_min_max_add(reg, &fake_reg);
scalar_min_max_add(reg, &fake_reg);
--
2.46.0
