Hello,
On 2022/12/5 9:19, Yang Jihong wrote:
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; } ... }
.
I see that there are emails from the community talking about the same problem, and come up with a solution: https://lore.kernel.org/bpf/20221202103620.1915679-1-bjorn@kernel.org/T/
will remove this patch based on that patch.
Thanks, Yang
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