From 44b7f7151dfc2e0947f39ed4b9bc4b0c2ccd46fc Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Sat, 15 Jun 2024 10:46:32 -0700 Subject: [PATCH] bpf: Add missed var_off setting in coerce_subreg_to_size_sx() In coerce_subreg_to_size_sx(), for the case where upper sign extension bits are the same for smax32 and smin32 values, we missed to setup properly. This is especially problematic if both smax32 and smin32's sign extension bits are 1. The following is a simple example illustrating the inconsistent verifier states due to missed var_off: 0: (85) call bpf_get_prandom_u32#7 ; R0_w=scalar() 1: (bf) r3 = r0 ; R0_w=scalar(id=1) R3_w=scalar(id=1) 2: (57) r3 &= 15 ; R3_w=scalar(smin=smin32=0,smax=umax=smax32=umax32=15,var_off=(0x0; 0xf)) 3: (47) r3 |= 128 ; R3_w=scalar(smin=umin=smin32=umin32=128,smax=umax=smax32=umax32=143,var_off=(0x80; 0xf)) 4: (bc) w7 = (s8)w3 REG INVARIANTS VIOLATION (alu): range bounds violation u64=[0xffffff80, 0x8f] s64=[0xffffff80, 0x8f] u32=[0xffffff80, 0x8f] s32=[0x80, 0xffffff8f] var_off=(0x80, 0xf) The var_off=(0x80, 0xf) is not correct, and the correct one should be var_off=(0xffffff80; 0xf) since from insn 3, we know that at insn 4, the sign extension bits will be 1. This patch fixed this issue by setting var_off properly. Fixes: 8100928c8814 ("bpf: Support new sign-extension mov insns") Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20240615174632.3995278-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 904ef5a03cf5..e0a398a97d32 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6281,6 +6281,7 @@ static void coerce_subreg_to_size_sx(struct bpf_reg_state *reg, int size) reg->s32_max_value = s32_max; reg->u32_min_value = (u32)s32_min; reg->u32_max_value = (u32)s32_max; + reg->var_off = tnum_subreg(tnum_range(s32_min, s32_max)); return; }