From: Eduard Zingerman eddyz87@gmail.com

[ 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@gmail.com Signed-off-by: Lonial Con kongln9170@gmail.com Signed-off-by: Eduard Zingerman eddyz87@gmail.com Signed-off-by: Andrii Nakryiko andrii@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Daniel Borkmann daniel@iogearbox.net Closes: https://lore.kernel.org/bpf/7e2aa30a62d740db182c170fdd8f81c596df280d.camel@g... Link: https://lore.kernel.org/bpf/20240924210844.1758441-1-eddyz87@gmail.com 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@suse.com --- 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; + } })); }