From c9543019ff8b880e9ce847a132ec9ebee7a3d986 Mon Sep 17 00:00:00 2001 From: Eduard Zingerman Date: Tue, 24 Sep 2024 14:08:43 -0700 Subject: [PATCH] bpf: sync_linked_regs() must preserve subreg_def commit e9bd9c498cb0f5843996dbe5cbce7a1836a83c70 upstream. 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 Signed-off-by: Lonial Con Signed-off-by: Eduard Zingerman Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann Acked-by: Daniel Borkmann Closes: https://lore.kernel.org/bpf/7e2aa30a62d740db182c170fdd8f81c596df280d.camel@gmail.com 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 Signed-off-by: Greg Kroah-Hartman --- 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 d1d5189a6..4500cd97f 100755 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -8168,8 +8168,11 @@ 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; + } })); }