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kallsyms: cache bpf symbols to avoid quadratic iteration #10892

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kallsyms: cache bpf symbols to avoid quadratic iteration #10892

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16 changes: 16 additions & 0 deletions include/linux/filter.h
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Original file line number Diff line number Diff line change
Expand Up @@ -648,6 +648,11 @@ static inline bool insn_is_cast_user(const struct bpf_insn *insn)
offsetof(TYPE, MEMBER); \
})

struct bpf_ksym_cache_entry {
unsigned long value;
char name[KSYM_NAME_LEN];
};

/* A struct sock_filter is architecture independent. */
struct compat_sock_fprog {
u16 len;
Expand Down Expand Up @@ -1381,6 +1386,9 @@ int __bpf_address_lookup(unsigned long addr, unsigned long *size,
bool is_bpf_text_address(unsigned long addr);
int bpf_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
char *sym);

int bpf_get_all_kallsyms(struct bpf_ksym_cache_entry **cache_ptr,
unsigned int *count_ptr);
struct bpf_prog *bpf_prog_ksym_find(unsigned long addr);

static inline int
Expand Down Expand Up @@ -1449,6 +1457,14 @@ static inline int bpf_get_kallsym(unsigned int symnum, unsigned long *value,
return -ERANGE;
}

static inline int bpf_get_all_kallsyms(struct bpf_ksym_cache_entry **cache_ptr,
unsigned int *count_ptr)
{
*cache_ptr = NULL;
*count_ptr = 0;
return 0;
}

static inline struct bpf_prog *bpf_prog_ksym_find(unsigned long addr)
{
return NULL;
Expand Down
46 changes: 46 additions & 0 deletions kernel/bpf/core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -825,6 +825,52 @@ int bpf_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
return ret;
}

int bpf_get_all_kallsyms(struct bpf_ksym_cache_entry **cache_ptr,
unsigned int *count_ptr)
{
struct bpf_ksym_cache_entry *cache;
struct bpf_ksym *ksym;
unsigned int count = 0;
unsigned int i = 0;

if (!bpf_jit_kallsyms_enabled()) {
*cache_ptr = NULL;
*count_ptr = 0;
return 0;
}

rcu_read_lock();
list_for_each_entry_rcu(ksym, &bpf_kallsyms, lnode)
count++;
rcu_read_unlock();

if (count == 0) {
*cache_ptr = NULL;
*count_ptr = 0;
return 0;
}

cache = kvmalloc_array(count, sizeof(*cache), GFP_KERNEL);
if (!cache)
return -ENOMEM;

rcu_read_lock();
list_for_each_entry_rcu(ksym, &bpf_kallsyms, lnode) {
if (i >= count) {
/* List grew since we counted, oh well */
break;
}
strscpy(cache[i].name, ksym->name, KSYM_NAME_LEN);
cache[i].value = ksym->start;
i++;
}
rcu_read_unlock();

*cache_ptr = cache;
*count_ptr = i;
return 0;
}

int bpf_jit_add_poke_descriptor(struct bpf_prog *prog,
struct bpf_jit_poke_descriptor *poke)
{
Expand Down
34 changes: 32 additions & 2 deletions kernel/kallsyms.c
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Original file line number Diff line number Diff line change
Expand Up @@ -566,6 +566,8 @@ struct kallsym_iter {
char module_name[MODULE_NAME_LEN];
int exported;
int show_value;
struct bpf_ksym_cache_entry *bpf_cache;
unsigned int bpf_cache_count;
};

static int get_ksymbol_mod(struct kallsym_iter *iter)
Expand Down Expand Up @@ -603,11 +605,27 @@ static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)

static int get_ksymbol_bpf(struct kallsym_iter *iter)
{
unsigned int index = iter->pos - iter->pos_ftrace_mod_end;
int ret;

if (iter->bpf_cache) {
if (index >= iter->bpf_cache_count) {
iter->pos_bpf_end = iter->pos;
return 0;
}

strscpy(iter->module_name, "bpf", MODULE_NAME_LEN);
iter->exported = 0;
strscpy(iter->name, iter->bpf_cache[index].name, KSYM_NAME_LEN);
iter->value = iter->bpf_cache[index].value;
iter->type = BPF_SYM_ELF_TYPE;

return 1;
}

strscpy(iter->module_name, "bpf", MODULE_NAME_LEN);
iter->exported = 0;
ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
ret = bpf_get_kallsym(index,
&iter->value, &iter->type,
iter->name);
if (ret < 0) {
Expand Down Expand Up @@ -862,9 +880,21 @@ static int kallsyms_open(struct inode *inode, struct file *file)
* the result here at open time.
*/
iter->show_value = kallsyms_show_value(file->f_cred);

bpf_get_all_kallsyms(&iter->bpf_cache, &iter->bpf_cache_count);

return 0;
}

static int kallsyms_release(struct inode *inode, struct file *file)
{
struct seq_file *m = file->private_data;
struct kallsym_iter *iter = m->private;

kvfree(iter->bpf_cache);
return seq_release_private(inode, file);
}

#ifdef CONFIG_KGDB_KDB
const char *kdb_walk_kallsyms(loff_t *pos)
{
Expand All @@ -889,7 +919,7 @@ static const struct proc_ops kallsyms_proc_ops = {
.proc_open = kallsyms_open,
.proc_read = seq_read,
.proc_lseek = seq_lseek,
.proc_release = seq_release_private,
.proc_release = kallsyms_release,
};

static int __init kallsyms_init(void)
Expand Down