[PATCH 5.18 0480/1095] bpf: Populate pairs of btf_id and destructor kfunc in btf

Greg Kroah-Hartman
2022-08-15T21:18:51Z

From: Kumar Kartikeya Dwivedi <memxor@gmail.com>

[ Upstream commit 5ce937d613a423ca3102f53d9f3daf4210c1b6e2 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/btf.h | 17 +++++++
kernel/bpf/btf.c | 108 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 125 insertions(+)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 19c297f9a52f..fea424681d66 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -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
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 58fd6896c403..57e3d9443ff3 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -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);
@@ -7022,6 +7040,96 @@ 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
--
2.35.1