On 2/8/22 10:20 PM, Hou Tao wrote:
Hi,
On 2/9/2022 12:57 AM, Yonghong Song wrote:
On 2/8/22 4:33 AM, Hou Tao wrote:
Now kfunc call uses s32 to represent the offset between the address
of kfunc and __bpf_call_base, but it doesn't check whether or not
s32 will be overflowed, so add an extra checking to reject these
invalid kfunc calls.
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
v2:
* instead of checking the overflow in selftests, just reject
these kfunc calls directly in verifier
v1: https://lore.kernel.org/bpf/20220206043107.18549-1-houtao1@xxxxxxxxxx
---
kernel/bpf/verifier.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a39eedecc93a..fd836e64b701 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1832,6 +1832,13 @@ static struct btf *find_kfunc_desc_btf(struct
bpf_verifier_env *env,
return btf_vmlinux ?: ERR_PTR(-ENOENT);
}
+static inline bool is_kfunc_call_imm_overflowed(unsigned long addr)
+{
+ unsigned long offset = BPF_CALL_IMM(addr);
+
+ return (unsigned long)(s32)offset != offset;
+}
+
static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16
offset)
{
const struct btf_type *func, *func_proto;
@@ -1925,6 +1932,12 @@ static int add_kfunc_call(struct bpf_verifier_env
*env, u32 func_id, s16 offset)
return -EINVAL;
}
+ if (is_kfunc_call_imm_overflowed(addr)) {
+ verbose(env, "address of kernel function %s is out of range\n",
+ func_name);
+ return -EINVAL;
+ }
+
desc = &tab->descs[tab->nr_descs++];
desc->func_id = func_id;
desc->imm = BPF_CALL_IMM(addr);
Thanks, I would like to call BPF_CALL_IMM only once and keep checking overflow
and setting desc->imm close to each other. How about the following
not-compile-tested code
unsigned long call_imm;
...
call_imm = BPF_CALL_IMM(addr);
/* some comment here */
if ((unsigned long)(s32)call_imm != call_imm) {
verbose(env, ...);
return -EINVAL;
} else {
desc->imm = call_imm;
}
call BPF_CALL_IMM once is OK for me. but I don't think the else branch is
unnecessary and it make the code
ugly. Can we just return directly when found that imm is overflowed ?
call_imm = BPF_CALL_IMM(addr);
/* Check whether or not the relative offset overflows desc->imm */
if ((unsigned long)(s32)call_imm != call_imm) {
verbose(env, "address of kernel function %s is out of range\n",
func_name);
return -EINVAL;
}
desc = &tab->descs[tab->nr_descs++];
desc->func_id = func_id;
desc->imm = call_imm;
Sure. Your above change looks good. My change is just
an illustration :-).
.
