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bpf: Populate pairs of btf_id and destructor kfunc in btf

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To support storing referenced PTR_TO_BTF_ID in maps, we require
associating a specific BTF ID with a 'destructor' kfunc. This is because
we need to release a live referenced pointer at a certain offset in map
value from the map destruction path, otherwise we end up leaking
resources.

Hence, introduce support for passing an array of btf_id, kfunc_btf_id
pairs that denote a BTF ID and its associated release function. Then,
add an accessor 'btf_find_dtor_kfunc' which can be used to look up the
destructor kfunc of a certain BTF ID. If found, we can use it to free
the object from the map free path.

The registration of these pairs also serve as a whitelist of structures
which are allowed as referenced PTR_TO_BTF_ID in a BPF map, because
without finding the destructor kfunc, we will bail and return an error.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220424214901.2743946-7-memxor@gmail.com
This commit is contained in:
Kumar Kartikeya Dwivedi 2022-04-25 03:18:54 +05:30 committed by Alexei Starovoitov
parent 4d7d7f69f4
commit 5ce937d613
2 changed files with 125 additions and 0 deletions
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17
include/linux/btf.h
View file

@ -40,6 +40,11 @@ struct btf_kfunc_id_set {
};
};
struct btf_id_dtor_kfunc {
u32 btf_id;
u32 kfunc_btf_id;
};
extern const struct file_operations btf_fops;
void btf_get(struct btf *btf);
@ -346,6 +351,9 @@ bool btf_kfunc_id_set_contains(const struct btf *btf,
enum btf_kfunc_type type, u32 kfunc_btf_id);
int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
const struct btf_kfunc_id_set *s);
s32 btf_find_dtor_kfunc(struct btf *btf, u32 btf_id);
int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors, u32 add_cnt,
struct module *owner);
#else
static inline const struct btf_type *btf_type_by_id(const struct btf *btf,
u32 type_id)
@ -369,6 +377,15 @@ static inline int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
{
return 0;
}
static inline s32 btf_find_dtor_kfunc(struct btf *btf, u32 btf_id)
{
return -ENOENT;
}
static inline int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors,
u32 add_cnt, struct module *owner)
{
return 0;
}
#endif
#endif

108
kernel/bpf/btf.c
View file

@ -207,12 +207,18 @@ enum btf_kfunc_hook {
enum {
BTF_KFUNC_SET_MAX_CNT = 32,
BTF_DTOR_KFUNC_MAX_CNT = 256,
};
struct btf_kfunc_set_tab {
struct btf_id_set *sets[BTF_KFUNC_HOOK_MAX][BTF_KFUNC_TYPE_MAX];
};
struct btf_id_dtor_kfunc_tab {
u32 cnt;
struct btf_id_dtor_kfunc dtors[];
};
struct btf {
void *data;
struct btf_type **types;
@ -228,6 +234,7 @@ struct btf {
u32 id;
struct rcu_head rcu;
struct btf_kfunc_set_tab *kfunc_set_tab;
struct btf_id_dtor_kfunc_tab *dtor_kfunc_tab;
/* split BTF support */
struct btf *base_btf;
@ -1616,8 +1623,19 @@ static void btf_free_kfunc_set_tab(struct btf *btf)
btf->kfunc_set_tab = NULL;
}
static void btf_free_dtor_kfunc_tab(struct btf *btf)
{
struct btf_id_dtor_kfunc_tab *tab = btf->dtor_kfunc_tab;
if (!tab)
return;
kfree(tab);
btf->dtor_kfunc_tab = NULL;
}
static void btf_free(struct btf *btf)
{
btf_free_dtor_kfunc_tab(btf);
btf_free_kfunc_set_tab(btf);
kvfree(btf->types);
kvfree(btf->resolved_sizes);
@ -7076,6 +7094,96 @@ int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
}
EXPORT_SYMBOL_GPL(register_btf_kfunc_id_set);
s32 btf_find_dtor_kfunc(struct btf *btf, u32 btf_id)
{
struct btf_id_dtor_kfunc_tab *tab = btf->dtor_kfunc_tab;
struct btf_id_dtor_kfunc *dtor;
if (!tab)
return -ENOENT;
/* Even though the size of tab->dtors[0] is > sizeof(u32), we only need
* to compare the first u32 with btf_id, so we can reuse btf_id_cmp_func.
*/
BUILD_BUG_ON(offsetof(struct btf_id_dtor_kfunc, btf_id) != 0);
dtor = bsearch(&btf_id, tab->dtors, tab->cnt, sizeof(tab->dtors[0]), btf_id_cmp_func);
if (!dtor)
return -ENOENT;
return dtor->kfunc_btf_id;
}
/* This function must be invoked only from initcalls/module init functions */
int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors, u32 add_cnt,
struct module *owner)
{
struct btf_id_dtor_kfunc_tab *tab;
struct btf *btf;
u32 tab_cnt;
int ret;
btf = btf_get_module_btf(owner);
if (!btf) {
if (!owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
pr_err("missing vmlinux BTF, cannot register dtor kfuncs\n");
return -ENOENT;
}
if (owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES)) {
pr_err("missing module BTF, cannot register dtor kfuncs\n");
return -ENOENT;
}
return 0;
}
if (IS_ERR(btf))
return PTR_ERR(btf);
if (add_cnt >= BTF_DTOR_KFUNC_MAX_CNT) {
pr_err("cannot register more than %d kfunc destructors\n", BTF_DTOR_KFUNC_MAX_CNT);
ret = -E2BIG;
goto end;
}
tab = btf->dtor_kfunc_tab;
/* Only one call allowed for modules */
if (WARN_ON_ONCE(tab && btf_is_module(btf))) {
ret = -EINVAL;
goto end;
}
tab_cnt = tab ? tab->cnt : 0;
if (tab_cnt > U32_MAX - add_cnt) {
ret = -EOVERFLOW;
goto end;
}
if (tab_cnt + add_cnt >= BTF_DTOR_KFUNC_MAX_CNT) {
pr_err("cannot register more than %d kfunc destructors\n", BTF_DTOR_KFUNC_MAX_CNT);
ret = -E2BIG;
goto end;
}
tab = krealloc(btf->dtor_kfunc_tab,
offsetof(struct btf_id_dtor_kfunc_tab, dtors[tab_cnt + add_cnt]),
GFP_KERNEL | __GFP_NOWARN);
if (!tab) {
ret = -ENOMEM;
goto end;
}
if (!btf->dtor_kfunc_tab)
tab->cnt = 0;
btf->dtor_kfunc_tab = tab;
memcpy(tab->dtors + tab->cnt, dtors, add_cnt * sizeof(tab->dtors[0]));
tab->cnt += add_cnt;
sort(tab->dtors, tab->cnt, sizeof(tab->dtors[0]), btf_id_cmp_func, NULL);
return 0;
end:
btf_free_dtor_kfunc_tab(btf);
btf_put(btf);
return ret;
}
EXPORT_SYMBOL_GPL(register_btf_id_dtor_kfuncs);
#define MAX_TYPES_ARE_COMPAT_DEPTH 2
static