bpf: Allow to resolve bpf trampoline and dispatcher in unwind

When unwinding the stack we need to identify each address
to successfully continue. Adding latch tree to keep trampolines
for quick lookup during the unwind.

The patch uses first 48 bytes for latch tree node, leaving 4048
bytes from the rest of the page for trampoline or dispatcher
generated code.

It's still enough not to affect trampoline and dispatcher progs
maximum counts.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200123161508.915203-3-jolsa@kernel.org

1 files changed, 72 insertions, 8 deletions

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index eb64c245052b..6b264a92064b 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -4,6 +4,7 @@
 #include <linux/bpf.h>
 #include <linux/filter.h>
 #include <linux/ftrace.h>
+#include <linux/rbtree_latch.h>
 
 /* dummy _ops. The verifier will operate on target program's ops. */
 const struct bpf_verifier_ops bpf_extension_verifier_ops = {
@@ -16,11 +17,12 @@ const struct bpf_prog_ops bpf_extension_prog_ops = {
 #define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS)
 
 static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];
+static struct latch_tree_root image_tree __cacheline_aligned;
 
-/* serializes access to trampoline_table */
+/* serializes access to trampoline_table and image_tree */
 static DEFINE_MUTEX(trampoline_mutex);
 
-void *bpf_jit_alloc_exec_page(void)
+static void *bpf_jit_alloc_exec_page(void)
 {
 	void *image;
 
@@ -36,6 +38,64 @@ void *bpf_jit_alloc_exec_page(void)
 	return image;
 }
 
+static __always_inline bool image_tree_less(struct latch_tree_node *a,
+				      struct latch_tree_node *b)
+{
+	struct bpf_image *ia = container_of(a, struct bpf_image, tnode);
+	struct bpf_image *ib = container_of(b, struct bpf_image, tnode);
+
+	return ia < ib;
+}
+
+static __always_inline int image_tree_comp(void *addr, struct latch_tree_node *n)
+{
+	void *image = container_of(n, struct bpf_image, tnode);
+
+	if (addr < image)
+		return -1;
+	if (addr >= image + PAGE_SIZE)
+		return 1;
+
+	return 0;
+}
+
+static const struct latch_tree_ops image_tree_ops = {
+	.less	= image_tree_less,
+	.comp	= image_tree_comp,
+};
+
+static void *__bpf_image_alloc(bool lock)
+{
+	struct bpf_image *image;
+
+	image = bpf_jit_alloc_exec_page();
+	if (!image)
+		return NULL;
+
+	if (lock)
+		mutex_lock(&trampoline_mutex);
+	latch_tree_insert(&image->tnode, &image_tree, &image_tree_ops);
+	if (lock)
+		mutex_unlock(&trampoline_mutex);
+	return image->data;
+}
+
+void *bpf_image_alloc(void)
+{
+	return __bpf_image_alloc(true);
+}
+
+bool is_bpf_image_address(unsigned long addr)
+{
+	bool ret;
+
+	rcu_read_lock();
+	ret = latch_tree_find((void *) addr, &image_tree, &image_tree_ops) != NULL;
+	rcu_read_unlock();
+
+	return ret;
+}
+
 struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
 {
 	struct bpf_trampoline *tr;
@@ -56,7 +116,7 @@ struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
 		goto out;
 
 	/* is_root was checked earlier. No need for bpf_jit_charge_modmem() */
-	image = bpf_jit_alloc_exec_page();
+	image = __bpf_image_alloc(false);
 	if (!image) {
 		kfree(tr);
 		tr = NULL;
@@ -131,14 +191,14 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
 }
 
 /* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
- * bytes on x86.  Pick a number to fit into PAGE_SIZE / 2
+ * bytes on x86.  Pick a number to fit into BPF_IMAGE_SIZE / 2
  */
 #define BPF_MAX_TRAMP_PROGS 40
 
 static int bpf_trampoline_update(struct bpf_trampoline *tr)
 {
-	void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2;
-	void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2;
+	void *old_image = tr->image + ((tr->selector + 1) & 1) * BPF_IMAGE_SIZE/2;
+	void *new_image = tr->image + (tr->selector & 1) * BPF_IMAGE_SIZE/2;
 	struct bpf_prog *progs_to_run[BPF_MAX_TRAMP_PROGS];
 	int fentry_cnt = tr->progs_cnt[BPF_TRAMP_FENTRY];
 	int fexit_cnt = tr->progs_cnt[BPF_TRAMP_FEXIT];
@@ -174,7 +234,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
 	 */
 	synchronize_rcu_tasks();
 
-	err = arch_prepare_bpf_trampoline(new_image, new_image + PAGE_SIZE / 2,
+	err = arch_prepare_bpf_trampoline(new_image, new_image + BPF_IMAGE_SIZE / 2,
 					  &tr->func.model, flags,
 					  fentry, fentry_cnt,
 					  fexit, fexit_cnt,
@@ -284,6 +344,8 @@ out:
 
 void bpf_trampoline_put(struct bpf_trampoline *tr)
 {
+	struct bpf_image *image;
+
 	if (!tr)
 		return;
 	mutex_lock(&trampoline_mutex);
@@ -294,9 +356,11 @@ void bpf_trampoline_put(struct bpf_trampoline *tr)
 		goto out;
 	if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT])))
 		goto out;
+	image = container_of(tr->image, struct bpf_image, data);
+	latch_tree_erase(&image->tnode, &image_tree, &image_tree_ops);
 	/* wait for tasks to get out of trampoline before freeing it */
 	synchronize_rcu_tasks();
-	bpf_jit_free_exec(tr->image);
+	bpf_jit_free_exec(image);
 	hlist_del(&tr->hlist);
 	kfree(tr);
 out: