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;elsereturn 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;
} ... }
.