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Date: Sat, 3 Dec 2022 08:40:40 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Yang Jihong <yangjihong1@...wei.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>,
Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Shubham Bansal <illusionist.neo@...il.com>,
Russell King <linux@...linux.org.uk>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
Benjamin Tissoires <benjamin.tissoires@...hat.com>,
Kumar Kartikeya Dwivedi <memxor@...il.com>,
colin.i.king@...il.com, Artem Savkov <asavkov@...hat.com>,
Delyan Kratunov <delyank@...com>, bpf <bpf@...r.kernel.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
LKML <linux-kernel@...r.kernel.org>,
Network Development <netdev@...r.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 1/4] bpf: Adapt 32-bit return value kfunc for
32-bit ARM when zext extension
On Fri, Dec 2, 2022 at 6:58 PM Yang Jihong <yangjihong1@...wei.com> wrote:
>
>
>
> On 2022/11/29 0:41, Alexei Starovoitov wrote:
> > On Mon, Nov 28, 2022 at 4:40 AM Yang Jihong <yangjihong1@...wei.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@...wei.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.
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