On 4/26/2024 7:41 AM, Andrii Nakryiko wrote:
On Thu, Apr 11, 2024 at 5:24 AM Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> wrote:From: Xu Kuohai <xukuohai@xxxxxxxxxx> 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@xxxxxxxxxx> --- 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 05c7c5f2bec0..5393d576c76f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -9879,7 +9879,7 @@ 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;are all BPF programs treated as if they return int instead of long? If not, we probably should have a bool flag in bpf_retval_range whether comparison should be 32-bit or 64-bit?
It seems that when a fmod_return prog is attached to a kernel function that returns long value, the bpf prog should also return long value. To confirm it, I'll try to find an example or construct a case for this.
} static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx) -- 2.30.2
