From: Eduard Zingerman <eddyz87@xxxxxxxxx>
[ Upstream commit e9bd9c498cb0f5843996dbe5cbce7a1836a83c70 ]
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).
Fixes: 75748837b7e5 ("bpf: Propagate scalar ranges through register assignments.")
Reported-by: Lonial Con <kongln9170@xxxxxxxxx>
Signed-off-by: Lonial Con <kongln9170@xxxxxxxxx>
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Closes: https://lore.kernel.org/bpf/7e2aa30a62d740db182c170fdd8f81c596df280d.camel@xxxxxxxxx
Link: https://lore.kernel.org/bpf/20240924210844.1758441-1-eddyz87@xxxxxxxxx
shung-hsi.yu: sync_linked_regs() was called find_equal_scalars() before commit
4bf79f9be434 ("bpf: Track equal scalars history on per-instruction level"), and
modification is done because there is only a single call to
copy_register_state() before commit 98d7ca374ba4 ("bpf: Track delta between
"linked" registers.").
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx>
---
kernel/bpf/verifier.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3f47cfa17141..a3c3c66ca047 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -14497,8 +14497,11 @@ static void find_equal_scalars(struct bpf_verifier_state *vstate,
struct bpf_reg_state *reg;
bpf_for_each_reg_in_vstate(vstate, state, reg, ({
- if (reg->type == SCALAR_VALUE && reg->id == known_reg->id)
+ if (reg->type == SCALAR_VALUE && reg->id == known_reg->id) {
+ s32 saved_subreg_def = reg->subreg_def;
copy_register_state(reg, known_reg);
+ reg->subreg_def = saved_subreg_def;
+ }
}));
}
--
2.47.1
