On 7/24/20 2:36 PM, Maciej Fijalkowski wrote:
Previously, there was no need for poke descriptors being present in
subprogram's bpf_prog_aux struct since tailcalls were simply not allowed
in them. Each subprog is JITed independently so in order to enable
JITing such subprograms, simply copy poke descriptors from main program
to subprogram's poke tab.
Add also subprog's aux struct to the BPF map poke_progs list by calling
on it map_poke_track().
In case of any error, call the map_poke_untrack() on subprog's aux
structs that have already been registered to prog array map.
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
---
kernel/bpf/verifier.c | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9a6703bc3f36..3e931e3e2239 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9900,9 +9900,12 @@ static int jit_subprogs(struct bpf_verifier_env *env)
{
struct bpf_prog *prog = env->prog, **func, *tmp;
int i, j, subprog_start, subprog_end = 0, len, subprog;
+ struct bpf_map *map_ptr;
struct bpf_insn *insn;
void *old_bpf_func;
int err, num_exentries;
+ int last_poke_desc = 0;
+ int last_subprog = 0;
if (env->subprog_cnt <= 1)
return 0;
@@ -9967,6 +9970,26 @@ static int jit_subprogs(struct bpf_verifier_env *env)
func[i]->aux->btf = prog->aux->btf;
func[i]->aux->func_info = prog->aux->func_info;
+ for (j = 0; j < prog->aux->size_poke_tab; j++) {
+ int ret;
+
+ ret = bpf_jit_add_poke_descriptor(func[i],
+ &prog->aux->poke_tab[j]);
+ if (ret < 0) {
+ verbose(env, "adding tail call poke descriptor failed\n");
+ goto out_untrack;
+ }
+ map_ptr = func[i]->aux->poke_tab[j].tail_call.map;
+ ret = map_ptr->ops->map_poke_track(map_ptr, func[i]->aux);
+ if (ret < 0) {
+ verbose(env, "tracking tail call prog failed\n");
+ goto out_untrack;
+ }
+ last_poke_desc = j;
+ }
+ last_poke_desc = 0;
+ last_subprog = i;
+
/* Use bpf_prog_F_tag to indicate functions in stack traces.
* Long term would need debug info to populate names
*/
@@ -10059,7 +10082,25 @@ static int jit_subprogs(struct bpf_verifier_env *env)
prog->aux->func_cnt = env->subprog_cnt;
bpf_prog_free_unused_jited_linfo(prog);
return 0;
+out_untrack:
+ /* this loop is only for handling the case where propagating all of
+ * the main prog's poke descs was not successful for a particular
+ * subprog; last_poke_desc is zeroed once we walked through all
+ * of the poke descs; if last_poke_desc != 0 then 'i' is valid since
+ * it is pointing to the subprog that we were at when got an error
+ */
+ while (last_poke_desc--) {
+ map_ptr = func[i]->aux->poke_tab[last_poke_desc].tail_call.map;
+ map_ptr->ops->map_poke_untrack(map_ptr, func[i]->aux);
+ }
+ last_subprog = i - 1;
out_free:
+ for (i = last_subprog; i >= 0; i--) {
+ for (j = 0; j < prog->aux->size_poke_tab; j++) {
+ map_ptr = func[i]->aux->poke_tab[j].tail_call.map;
+ map_ptr->ops->map_poke_untrack(map_ptr, func[i]->aux);
+ }
+ }
After staring at this code for a while, the logic looks correct to me, but feels overly
complicated with making sure all the corner cases do function above. I wonder, why didn't
you consider just something like ...
for (i = 0; i < env->subprog_cnt; i++)
if (func[i]) {
for (j = 0; j < func[i]->aux->size_poke_tab; j++) {
map_ptr = func[i]->aux->poke_tab[j].tail_call.map;
map_ptr->ops->map_poke_untrack(map_ptr, func[i]->aux);
}
bpf_jit_free(func[i]);
}
... instead of last_poke_desc/last_subprog tracking and the fallthrough trick above. Am
I missing something?
for (i = 0; i < env->subprog_cnt; i++)
if (func[i])
bpf_jit_free(func[i]);
