Messages in this thread |  | | Subject | Re: [PATCH bpf-next v3 1/4] bpf: Adapt 32-bit return value kfunc for 32-bit ARM when zext extension | From | Yang Jihong <> | Date | Mon, 5 Dec 2022 09:19:40 +0800 |
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On 2022/12/4 0:40, Alexei Starovoitov wrote: > On Fri, Dec 2, 2022 at 6:58 PM Yang Jihong <yangjihong1@huawei.com> wrote: >> >> >> >> On 2022/11/29 0:41, Alexei Starovoitov wrote: >>> On Mon, Nov 28, 2022 at 4:40 AM Yang Jihong <yangjihong1@huawei.com> wrote: >>>> >>>> >>>> >>>> On 2022/11/28 9:57, Alexei Starovoitov wrote: >>>>> On Sat, Nov 26, 2022 at 05:45:27PM +0800, Yang Jihong wrote: >>>>>> For ARM32 architecture, if data width of kfunc return value is 32 bits, >>>>>> need to do explicit zero extension for high 32-bit, insn_def_regno should >>>>>> return dst_reg for BPF_JMP type of BPF_PSEUDO_KFUNC_CALL. Otherwise, >>>>>> opt_subreg_zext_lo32_rnd_hi32 returns -EFAULT, resulting in BPF failure. >>>>>> >>>>>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com> >>>>>> --- >>>>>> kernel/bpf/verifier.c | 44 ++++++++++++++++++++++++++++++++++++++++--- >>>>>> 1 file changed, 41 insertions(+), 3 deletions(-) >>>>>> >>>>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >>>>>> index 264b3dc714cc..193ea927aa69 100644 >>>>>> --- a/kernel/bpf/verifier.c >>>>>> +++ b/kernel/bpf/verifier.c >>>>>> @@ -1927,6 +1927,21 @@ find_kfunc_desc(const struct bpf_prog *prog, u32 func_id, u16 offset) >>>>>> sizeof(tab->descs[0]), kfunc_desc_cmp_by_id_off); >>>>>> } >>>>>> >>>>>> +static int kfunc_desc_cmp_by_imm(const void *a, const void *b); >>>>>> + >>>>>> +static const struct bpf_kfunc_desc * >>>>>> +find_kfunc_desc_by_imm(const struct bpf_prog *prog, s32 imm) >>>>>> +{ >>>>>> + struct bpf_kfunc_desc desc = { >>>>>> + .imm = imm, >>>>>> + }; >>>>>> + struct bpf_kfunc_desc_tab *tab; >>>>>> + >>>>>> + tab = prog->aux->kfunc_tab; >>>>>> + return bsearch(&desc, tab->descs, tab->nr_descs, >>>>>> + sizeof(tab->descs[0]), kfunc_desc_cmp_by_imm); >>>>>> +} >>>>>> + >>>>>> static struct btf *__find_kfunc_desc_btf(struct bpf_verifier_env *env, >>>>>> s16 offset) >>>>>> { >>>>>> @@ -2342,6 +2357,13 @@ static bool is_reg64(struct bpf_verifier_env *env, struct bpf_insn *insn, >>>>>> */ >>>>>> if (insn->src_reg == BPF_PSEUDO_CALL) >>>>>> return false; >>>>>> + >>>>>> + /* Kfunc call will reach here because of insn_has_def32, >>>>>> + * conservatively return TRUE. >>>>>> + */ >>>>>> + if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) >>>>>> + return true; >>>>>> + >>>>>> /* Helper call will reach here because of arg type >>>>>> * check, conservatively return TRUE. >>>>>> */ >>>>>> @@ -2405,10 +2427,26 @@ static bool is_reg64(struct bpf_verifier_env *env, struct bpf_insn *insn, >>>>>> } >>>>>> >>>>>> /* Return the regno defined by the insn, or -1. */ >>>>>> -static int insn_def_regno(const struct bpf_insn *insn) >>>>>> +static int insn_def_regno(struct bpf_verifier_env *env, const struct bpf_insn *insn) >>>>>> { >>>>>> switch (BPF_CLASS(insn->code)) { >>>>>> case BPF_JMP: >>>>>> + if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) { >>>>>> + const struct bpf_kfunc_desc *desc; >>>>>> + >>>>>> + /* The value of desc cannot be NULL */ >>>>>> + desc = find_kfunc_desc_by_imm(env->prog, insn->imm); >>>>>> + >>>>>> + /* A kfunc can return void. >>>>>> + * The btf type of the kfunc's return value needs >>>>>> + * to be checked against "void" first >>>>>> + */ >>>>>> + if (desc->func_model.ret_size == 0) >>>>>> + return -1; >>>>>> + else >>>>>> + return insn->dst_reg; >>>>>> + } >>>>>> + fallthrough; >>>>> >>>>> I cannot make any sense of this patch. >>>>> insn->dst_reg above is 0. >>>>> The kfunc call doesn't define a register from insn_def_regno() pov. >>>>> >>>>> Are you hacking insn_def_regno() to return 0 so that >>>>> if (WARN_ON(load_reg == -1)) { >>>>> verbose(env, "verifier bug. zext_dst is set, but no reg is defined\n"); >>>>> return -EFAULT; >>>>> } >>>>> in opt_subreg_zext_lo32_rnd_hi32() doesn't trigger ? >>>>> >>>>> But this verifier message should have been a hint that you need >>>>> to analyze why zext_dst is set on this kfunc call. >>>>> Maybe it shouldn't ? >>>>> Did you analyze the logic of mark_btf_func_reg_size() ? >>>> make r0 zext is not caused by mark_btf_func_reg_size. >>>> >>>> This problem occurs when running the kfunc_call_test_ref_btf_id test >>>> case in the 32-bit ARM environment. >>> >>> Why is it not failing on x86-32 ? >> Use the latest mainline kernel code to test on the x86_32 machine. The >> test also fails: >> >> # ./test_progs -t kfunc_call/kfunc_call_test_ref_btf_id >> Failed to load bpf_testmod.ko into the kernel: -8 >> WARNING! Selftests relying on bpf_testmod.ko will be skipped. >> libbpf: prog 'kfunc_call_test_ref_btf_id': BPF program load failed: >> Bad address >> libbpf: prog 'kfunc_call_test_ref_btf_id': -- BEGIN PROG LOAD LOG -- >> processed 25 insns (limit 1000000) max_states_per_insn 0 total_states >> 2 peak_states 2 mark_read 1 >> -- END PROG LOAD LOG -- >> libbpf: prog 'kfunc_call_test_ref_btf_id': failed to load: -14 >> libbpf: failed to load object 'kfunc_call_test' >> libbpf: failed to load BPF skeleton 'kfunc_call_test': -14 >> verify_success:FAIL:skel unexpected error: -14 >> >> Therefore, this problem also exists on x86_32: >> "verifier bug. zext_dst is set, but no reg is defined" > > The kernel returns -14 == EFAULT. > That's a completely different issue. It's the same problem. The opt_subreg_zext_lo32_rnd_hi32 function fails to check here and returns -EFAULT
opt_subreg_zext_lo32_rnd_hi32 { ... if (WARN_ON(load_reg == -1)) {
verbose(env, "verifier bug. zext_dst is set, but no reg is defined\n"); return -EFAULT;
} ... }
> . >
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