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 lsm does not return 64-bit values, this patch fixes it by changing
the compare between r0 and return range from 64-bit operation to 32-bit
operation for bpf lsm.
Fixes: 8fa4ecd49b81 ("bpf: enforce exact retval range on subprog/callback exit")
Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx>
---
kernel/bpf/verifier.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6f5d8ca995d6..19ef3d27dbb7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9995,9 +9995,13 @@ static bool in_rbtree_lock_required_cb(struct bpf_verifier_env *env)
return is_rbtree_lock_required_kfunc(kfunc_btf_id);
}
-static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg)
+static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg,
+ bool return_32bit)
{
- return range.minval <= reg->smin_value && reg->smax_value <= range.maxval;
+ if (return_32bit)
+ return range.minval <= reg->s32_min_value && reg->s32_max_value <= range.maxval;
+ else
+ return range.minval <= reg->smin_value && reg->smax_value <= range.maxval;
}
static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
@@ -10034,8 +10038,8 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
if (err)
return err;
- /* enforce R0 return value range */
- if (!retval_range_within(callee->callback_ret_range, r0)) {
+ /* enforce R0 return value range, and bpf_callback_t returns 64bit */
+ if (!retval_range_within(callee->callback_ret_range, r0, false)) {
verbose_invalid_scalar(env, r0, callee->callback_ret_range,
"At callback return", "R0");
return -EINVAL;
@@ -15718,6 +15722,7 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
int err;
struct bpf_func_state *frame = env->cur_state->frame[0];
const bool is_subprog = frame->subprogno;
+ bool return_32bit = false;
/* LSM and struct_ops func-ptr's return type could be "void" */
if (!is_subprog || frame->in_exception_callback_fn) {
@@ -15829,6 +15834,7 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
/* no restricted range, any return value is allowed */
if (range.minval == S32_MIN && range.maxval == S32_MAX)
return 0;
+ return_32bit = true;
} else if (!env->prog->aux->attach_func_proto->type) {
/* Make sure programs that attach to void
* hooks don't try to modify return value.
@@ -15859,7 +15865,7 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
if (err)
return err;
- if (!retval_range_within(range, reg)) {
+ if (!retval_range_within(range, reg, return_32bit)) {
verbose_invalid_scalar(env, reg, range, exit_ctx, reg_name);
if (!is_subprog &&
prog->expected_attach_type == BPF_LSM_CGROUP &&
--
2.30.2
