This is a note to let you know that I've just added the patch titled bpf: sync_linked_regs() must preserve subreg_def to the 6.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bpf-sync_linked_regs-must-preserve-subreg_def.patch and it can be found in the queue-6.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit cdc3e4354d579cac65f644e226a8e79efe53cfb6 Author: Eduard Zingerman <eddyz87@xxxxxxxxx> Date: Tue Sep 24 14:08:43 2024 -0700 bpf: sync_linked_regs() must preserve subreg_def [ 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 Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d5215cb1747f1..5c5dea5e137e7 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -15140,8 +15140,12 @@ static void find_equal_scalars(struct bpf_verifier_state *vstate, 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; @@ -15154,6 +15158,7 @@ static void find_equal_scalars(struct bpf_verifier_state *vstate, * otherwise another find_equal_scalars() 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);