[PATCH 03/15] bpf: Add struct bpf_ksym

Jiri Olsa
2020-03-02T14:32:19Z

Adding 'struct bpf_ksym' object that will carry the
kallsym information for bpf symbol. Adding the start
and end address to begin with. It will be used by
bpf_prog, bpf_trampoline, bpf_dispatcher.

The symbol_start/symbol_end values were originally used
to sort bpf_prog objects. For the address displayed in
/proc/kallsyms we are using prog->bpf_func.

I'm using the bpf_func for program symbol start instead
of the symbol_start, because it makes no difference for
sorting bpf_prog objects and we can use it directly as
an address for display it in /proc/kallsyms.

Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
include/linux/bpf.h | 6 ++++++
kernel/bpf/core.c | 28 ++++++++++++----------------
2 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index be7afccc9459..5ad8eea1cd37 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -462,6 +462,11 @@ int arch_prepare_bpf_trampoline(void *image, void *image_end,
u64 notrace __bpf_prog_enter(void);
void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start);

+struct bpf_ksym {
+ unsigned long start;
+ unsigned long end;
+};
+
enum bpf_tramp_prog_type {
BPF_TRAMP_FENTRY,
BPF_TRAMP_FEXIT,
@@ -643,6 +648,7 @@ struct bpf_prog_aux {
u32 size_poke_tab;
struct latch_tree_node ksym_tnode;
struct list_head ksym_lnode;
+ struct bpf_ksym ksym;
const struct bpf_prog_ops *ops;
struct bpf_map **used_maps;
struct bpf_prog *prog;
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 973a20d49749..e2dd2d87c987 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -523,18 +523,16 @@ int bpf_jit_kallsyms __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_DEFAULT_ON);
int bpf_jit_harden __read_mostly;
long bpf_jit_limit __read_mostly;

-static __always_inline void
-bpf_get_prog_addr_region(const struct bpf_prog *prog,
- unsigned long *symbol_start,
- unsigned long *symbol_end)
+static void
+bpf_prog_ksym_set_addr(struct bpf_prog *prog)
{
const struct bpf_binary_header *hdr = bpf_jit_binary_hdr(prog);
unsigned long addr = (unsigned long)hdr;

WARN_ON_ONCE(!bpf_prog_ebpf_jited(prog));

- *symbol_start = addr;
- *symbol_end = addr + hdr->pages * PAGE_SIZE;
+ prog->aux->ksym.start = (unsigned long) prog->bpf_func;
+ prog->aux->ksym.end = addr + hdr->pages * PAGE_SIZE;
}

void bpf_get_prog_name(const struct bpf_prog *prog, char *sym)
@@ -575,13 +573,10 @@ void bpf_get_prog_name(const struct bpf_prog *prog, char *sym)
static __always_inline unsigned long
bpf_get_prog_addr_start(struct latch_tree_node *n)
{
- unsigned long symbol_start, symbol_end;
const struct bpf_prog_aux *aux;

aux = container_of(n, struct bpf_prog_aux, ksym_tnode);
- bpf_get_prog_addr_region(aux->prog, &symbol_start, &symbol_end);
-
- return symbol_start;
+ return aux->ksym.start;
}

static __always_inline bool bpf_tree_less(struct latch_tree_node *a,
@@ -593,15 +588,13 @@ static __always_inline bool bpf_tree_less(struct latch_tree_node *a,
static __always_inline int bpf_tree_comp(void *key, struct latch_tree_node *n)
{
unsigned long val = (unsigned long)key;
- unsigned long symbol_start, symbol_end;
const struct bpf_prog_aux *aux;

aux = container_of(n, struct bpf_prog_aux, ksym_tnode);
- bpf_get_prog_addr_region(aux->prog, &symbol_start, &symbol_end);

- if (val < symbol_start)
+ if (val < aux->ksym.start)
return -1;
- if (val >= symbol_end)
+ if (val >= aux->ksym.end)
return 1;

return 0;
@@ -649,6 +642,8 @@ void bpf_prog_kallsyms_add(struct bpf_prog *fp)
!capable(CAP_SYS_ADMIN))
return;

+ bpf_prog_ksym_set_addr(fp);
+
spin_lock_bh(&bpf_lock);
bpf_prog_ksym_node_add(fp->aux);
spin_unlock_bh(&bpf_lock);
@@ -677,14 +672,15 @@ static struct bpf_prog *bpf_prog_kallsyms_find(unsigned long addr)
const char *__bpf_address_lookup(unsigned long addr, unsigned long *size,
unsigned long *off, char *sym)
{
- unsigned long symbol_start, symbol_end;
struct bpf_prog *prog;
char *ret = NULL;

rcu_read_lock();
prog = bpf_prog_kallsyms_find(addr);
if (prog) {
- bpf_get_prog_addr_region(prog, &symbol_start, &symbol_end);
+ unsigned long symbol_start = prog->aux->ksym.start;
+ unsigned long symbol_end = prog->aux->ksym.end;
+
bpf_get_prog_name(prog, sym);

ret = sym;
--
2.24.1