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Date: Mon, 15 Jul 2019 15:29:14 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jiong Wang <jiong.wang@...ronome.com>
Cc: Andrii Nakryiko <andriin@...com>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
Edward Cree <ecree@...arflare.com>,
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
Jakub Kicinski <jakub.kicinski@...ronome.com>,
bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
oss-drivers@...ronome.com
Subject: Re: [oss-drivers] Re: [RFC bpf-next 2/8] bpf: extend list based insn
patching infra to verification layer
On Mon, Jul 15, 2019 at 3:02 AM Jiong Wang <jiong.wang@...ronome.com> wrote:
>
>
> Andrii Nakryiko writes:
>
> > On Thu, Jul 11, 2019 at 5:20 AM Jiong Wang <jiong.wang@...ronome.com> wrote:
> >>
> >>
> >> Jiong Wang writes:
> >>
> >> > Andrii Nakryiko writes:
> >> >
> >> >> On Thu, Jul 4, 2019 at 2:32 PM Jiong Wang <jiong.wang@...ronome.com> wrote:
> >> >>>
> >> >>> Verification layer also needs to handle auxiliar info as well as adjusting
> >> >>> subprog start.
> >> >>>
> >> >>> At this layer, insns inside patch buffer could be jump, but they should
> >> >>> have been resolved, meaning they shouldn't jump to insn outside of the
> >> >>> patch buffer. Lineration function for this layer won't touch insns inside
> >> >>> patch buffer.
> >> >>>
> >> >>> Adjusting subprog is finished along with adjusting jump target when the
> >> >>> input will cover bpf to bpf call insn, re-register subprog start is cheap.
> >> >>> But adjustment when there is insn deleteion is not considered yet.
> >> >>>
> >> >>> Signed-off-by: Jiong Wang <jiong.wang@...ronome.com>
> >> >>> ---
> >> >>> kernel/bpf/verifier.c | 150 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >> >>> 1 file changed, 150 insertions(+)
> >> >>>
> >> >>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> >> >>> index a2e7637..2026d64 100644
> >> >>> --- a/kernel/bpf/verifier.c
> >> >>> +++ b/kernel/bpf/verifier.c
> >> >>> @@ -8350,6 +8350,156 @@ static void opt_hard_wire_dead_code_branches(struct bpf_verifier_env *env)
> >> >>> }
> >> >>> }
> >> >>>
> >> >>> +/* Linearize bpf list insn to array (verifier layer). */
> >> >>> +static struct bpf_verifier_env *
> >> >>> +verifier_linearize_list_insn(struct bpf_verifier_env *env,
> >> >>> + struct bpf_list_insn *list)
> >> >>
> >> >> It's unclear why this returns env back? It's not allocating a new env,
> >> >> so it's weird and unnecessary. Just return error code.
> >> >
> >> > The reason is I was thinking we have two layers in BPF, the core and the
> >> > verifier.
> >> >
> >> > For core layer (the relevant file is core.c), when doing patching, the
> >> > input is insn list and bpf_prog, the linearization should linearize the
> >> > insn list into insn array, and also whatever others affect inside bpf_prog
> >> > due to changing on insns, for example line info inside prog->aux. So the
> >> > return value is bpf_prog for core layer linearization hook.
> >> >
> >> > For verifier layer, it is similar, but the context if bpf_verifier_env, the
> >> > linearization hook should linearize the insn list, and also those affected
> >> > inside env, for example bpf_insn_aux_data, so the return value is
> >> > bpf_verifier_env, meaning returning an updated verifier context
> >> > (bpf_verifier_env) after insn list linearization.
> >>
> >> Realized your point is no new env is allocated, so just return error
> >> code. Yes, the env pointer is not changed, just internal data is
> >> updated. Return bpf_verifier_env mostly is trying to make the hook more
> >> clear that it returns an updated "context" where the linearization happens,
> >> for verifier layer, it is bpf_verifier_env, and for core layer, it is
> >> bpf_prog, so return value was designed to return these two types.
> >
> > Oh, I missed that core layer returns bpf_prog*. I think this is
> > confusing as hell and is very contrary to what one would expect. If
> > the function doesn't allocate those objects, it shouldn't return them,
> > except for rare cases of some accessor functions. Me reading this,
> > I'll always be suprised and will have to go skim code just to check
> > whether those functions really return new bpf_prog or
> > bpf_verifier_env, respectively.
>
> bpf_prog_realloc do return new bpf_prog, so we will need to return bpf_prog
> * for core layer.
Ah, I see, then it would make sense for core layer, but still is very
confusing for verifier_linearize_list_insn.
I still hope for unified solution, so it shouldn't matter. But it
pointed me to a bug in your code, see below.
>
> >
> > Please change them both to just return error code.
> >
> >>
> >> >
> >> > Make sense?
> >> >
> >> > Regards,
> >> > Jiong
> >> >
> >> >>
> >> >>> +{
> >> >>> + u32 *idx_map, idx, orig_cnt, fini_cnt = 0;
> >> >>> + struct bpf_subprog_info *new_subinfo;
> >> >>> + struct bpf_insn_aux_data *new_data;
> >> >>> + struct bpf_prog *prog = env->prog;
> >> >>> + struct bpf_verifier_env *ret_env;
> >> >>> + struct bpf_insn *insns, *insn;
> >> >>> + struct bpf_list_insn *elem;
> >> >>> + int ret;
> >> >>> +
> >> >>> + /* Calculate final size. */
> >> >>> + for (elem = list; elem; elem = elem->next)
> >> >>> + if (!(elem->flag & LIST_INSN_FLAG_REMOVED))
> >> >>> + fini_cnt++;
> >> >>> +
> >> >>> + orig_cnt = prog->len;
> >> >>> + insns = prog->insnsi;
> >> >>> + /* If prog length remains same, nothing else to do. */
> >> >>> + if (fini_cnt == orig_cnt) {
> >> >>> + for (insn = insns, elem = list; elem; elem = elem->next, insn++)
> >> >>> + *insn = elem->insn;
> >> >>> + return env;
> >> >>> + }
> >> >>> + /* Realloc insn buffer when necessary. */
> >> >>> + if (fini_cnt > orig_cnt)
> >> >>> + prog = bpf_prog_realloc(prog, bpf_prog_size(fini_cnt),
> >> >>> + GFP_USER);
> >> >>> + if (!prog)
> >> >>> + return ERR_PTR(-ENOMEM);
On realloc failure, prog will be non-NULL, so you need to handle error
properly (and propagate it, instead of returning -ENOMEM):
if (IS_ERR(prog))
return ERR_PTR(prog);
> >> >>> + insns = prog->insnsi;
> >> >>> + prog->len = fini_cnt;
> >> >>> + ret_env = env;
> >> >>> +
> >> >>> + /* idx_map[OLD_IDX] = NEW_IDX */
> >> >>> + idx_map = kvmalloc(orig_cnt * sizeof(u32), GFP_KERNEL);
> >> >>> + if (!idx_map)
> >> >>> + return ERR_PTR(-ENOMEM);
> >> >>> + memset(idx_map, 0xff, orig_cnt * sizeof(u32));
> >> >>> +
> >> >>> + /* Use the same alloc method used when allocating env->insn_aux_data. */
> >> >>> + new_data = vzalloc(array_size(sizeof(*new_data), fini_cnt));
> >> >>> + if (!new_data) {
> >> >>> + kvfree(idx_map);
> >> >>> + return ERR_PTR(-ENOMEM);
> >> >>> + }
> >> >>> +
> >> >>> + /* Copy over insn + calculate idx_map. */
> >> >>> + for (idx = 0, elem = list; elem; elem = elem->next) {
> >> >>> + int orig_idx = elem->orig_idx - 1;
> >> >>> +
> >> >>> + if (orig_idx >= 0) {
> >> >>> + idx_map[orig_idx] = idx;
> >> >>> +
> >> >>> + if (elem->flag & LIST_INSN_FLAG_REMOVED)
> >> >>> + continue;
> >> >>> +
> >> >>> + new_data[idx] = env->insn_aux_data[orig_idx];
> >> >>> +
> >> >>> + if (elem->flag & LIST_INSN_FLAG_PATCHED)
> >> >>> + new_data[idx].zext_dst =
> >> >>> + insn_has_def32(env, &elem->insn);
> >> >>> + } else {
> >> >>> + new_data[idx].seen = true;
> >> >>> + new_data[idx].zext_dst = insn_has_def32(env,
> >> >>> + &elem->insn);
> >> >>> + }
> >> >>> + insns[idx++] = elem->insn;
> >> >>> + }
> >> >>> +
> >> >>> + new_subinfo = kvzalloc(sizeof(env->subprog_info), GFP_KERNEL);
> >> >>> + if (!new_subinfo) {
> >> >>> + kvfree(idx_map);
> >> >>> + vfree(new_data);
> >> >>> + return ERR_PTR(-ENOMEM);
> >> >>> + }
> >> >>> + memcpy(new_subinfo, env->subprog_info, sizeof(env->subprog_info));
> >> >>> + memset(env->subprog_info, 0, sizeof(env->subprog_info));
> >> >>> + env->subprog_cnt = 0;
> >> >>> + env->prog = prog;
> >> >>> + ret = add_subprog(env, 0);
> >> >>> + if (ret < 0) {
> >> >>> + ret_env = ERR_PTR(ret);
> >> >>> + goto free_all_ret;
> >> >>> + }
> >> >>> + /* Relocate jumps using idx_map.
> >> >>> + * old_dst = jmp_insn.old_target + old_pc + 1;
> >> >>> + * new_dst = idx_map[old_dst] = jmp_insn.new_target + new_pc + 1;
> >> >>> + * jmp_insn.new_target = new_dst - new_pc - 1;
> >> >>> + */
> >> >>> + for (idx = 0, elem = list; elem; elem = elem->next) {
> >> >>> + int orig_idx = elem->orig_idx;
> >> >>> +
> >> >>> + if (elem->flag & LIST_INSN_FLAG_REMOVED)
> >> >>> + continue;
> >> >>> + if ((elem->flag & LIST_INSN_FLAG_PATCHED) || !orig_idx) {
> >> >>> + idx++;
> >> >>> + continue;
> >> >>> + }
> >> >>> +
> >> >>> + ret = bpf_jit_adj_imm_off(&insns[idx], orig_idx - 1, idx,
> >> >>> + idx_map);
> >> >>> + if (ret < 0) {
> >> >>> + ret_env = ERR_PTR(ret);
> >> >>> + goto free_all_ret;
> >> >>> + }
> >> >>> + /* Recalculate subprog start as we are at bpf2bpf call insn. */
> >> >>> + if (ret > 0) {
> >> >>> + ret = add_subprog(env, idx + insns[idx].imm + 1);
> >> >>> + if (ret < 0) {
> >> >>> + ret_env = ERR_PTR(ret);
> >> >>> + goto free_all_ret;
> >> >>> + }
> >> >>> + }
> >> >>> + idx++;
> >> >>> + }
> >> >>> + if (ret < 0) {
> >> >>> + ret_env = ERR_PTR(ret);
> >> >>> + goto free_all_ret;
> >> >>> + }
> >> >>> +
> >> >>> + env->subprog_info[env->subprog_cnt].start = fini_cnt;
> >> >>> + for (idx = 0; idx <= env->subprog_cnt; idx++)
> >> >>> + new_subinfo[idx].start = env->subprog_info[idx].start;
> >> >>> + memcpy(env->subprog_info, new_subinfo, sizeof(env->subprog_info));
> >> >>> +
> >> >>> + /* Adjust linfo.
> >> >>> + * FIXME: no support for insn removal at the moment.
> >> >>> + */
> >> >>> + if (prog->aux->nr_linfo) {
> >> >>> + struct bpf_line_info *linfo = prog->aux->linfo;
> >> >>> + u32 nr_linfo = prog->aux->nr_linfo;
> >> >>> +
> >> >>> + for (idx = 0; idx < nr_linfo; idx++)
> >> >>> + linfo[idx].insn_off = idx_map[linfo[idx].insn_off];
> >> >>> + }
> >> >>> + vfree(env->insn_aux_data);
> >> >>> + env->insn_aux_data = new_data;
> >> >>> + goto free_mem_list_ret;
> >> >>> +free_all_ret:
> >> >>> + vfree(new_data);
> >> >>> +free_mem_list_ret:
> >> >>> + kvfree(new_subinfo);
> >> >>> + kvfree(idx_map);
> >> >>> + return ret_env;
> >> >>> +}
> >> >>> +
> >> >>> static int opt_remove_dead_code(struct bpf_verifier_env *env)
> >> >>> {
> >> >>> struct bpf_insn_aux_data *aux_data = env->insn_aux_data;
> >> >>> --
> >> >>> 2.7.4
> >> >>>
> >>
>
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