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; > .
