[PATCH bpf-next v2 5/7] bpf: Fix compare error in function retval_range_within

[Xu Kuohai]

From: Xu Kuohai <xukuohai at huawei.com>

After checking lsm hook return range in verifier, the test case
"test_progs -t test_lsm" failed, and the failure log says:

libbpf: prog 'test_int_hook': BPF program load failed: Invalid argument
libbpf: prog 'test_int_hook': -- BEGIN PROG LOAD LOG --
0: R1=ctx() R10=fp0
; int BPF_PROG(test_int_hook, struct vm_area_struct *vma, @ lsm.c:89
0: (79) r0 = *(u64 *)(r1 +24)         ; R0_w=scalar(smin=smin32=-4095,smax=smax32=0) R1=ctx()

[...]

24: (b4) w0 = -1                      ; R0_w=0xffffffff
; int BPF_PROG(test_int_hook, struct vm_area_struct *vma, @ lsm.c:89
25: (95) exit
At program exit the register R0 has smin=4294967295 smax=4294967295 should have been in [-4095, 0]

It can be seen that instruction "w0 = -1" zero extended -1 to 64-bit
register r0, setting both smin and smax values of r0 to 4294967295.
This resulted in a false reject when r0 was checked with range [-4095, 0].

Given bpf_retval_range is a 32-bit range, this patch fixes it by
changing the compare between r0 and return range from 64-bit
operation to 32-bit operation.

Fixes: 8fa4ecd49b81 ("bpf: enforce exact retval range on subprog/callback exit")
Signed-off-by: Xu Kuohai <xukuohai at huawei.com>
---
 kernel/bpf/verifier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c3387357bc0d..36cd13982926 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9864,7 +9864,7 @@ static bool in_rbtree_lock_required_cb(struct bpf_verifier_env *env)
 
 static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg)
 {
-	return range.minval <= reg->smin_value && reg->smax_value <= range.maxval;
+	return range.minval <= reg->s32_min_value && reg->s32_max_value <= range.maxval;
 }
 
 static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
-- 
2.30.2