Message-Id: <20241101111948.1570547-1-xukuohai@huaweicloud.com>
Date: Fri,  1 Nov 2024 19:19:48 +0800
From: Xu Kuohai <xukuohai@...weicloud.com>
To: bpf@...r.kernel.org,
	netdev@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Yonghong Song <yonghong.song@...ux.dev>,
	Kui-Feng Lee <thinker.li@...il.com>
Subject: [PATCH bpf-next v2] bpf: Add kernel symbol for struct_ops trampoline

From: Xu Kuohai <xukuohai@...wei.com>

Without kernel symbols for struct_ops trampoline, the unwinder may
produce unexpected stacktraces.

For example, the x86 ORC and FP unwinders check if an IP is in kernel
text by verifying the presence of the IP's kernel symbol. When a
struct_ops trampoline address is encountered, the unwinder stops due
to the absence of symbol, resulting in an incomplete stacktrace that
consists only of direct and indirect child functions called from the
trampoline.

The arm64 unwinder is another example. While the arm64 unwinder can
proceed across a struct_ops trampoline address, the corresponding
symbol name is displayed as "unknown", which is confusing.

Thus, add kernel symbol for struct_ops trampoline. The name is
bpf_trampoline_<PROG_NAME>, where PROG_NAME is the name of the
struct_ops prog linked to the trampoline.

Below is a comparison of stacktraces captured on x86 by perf record,
before and after this patch.

Before:

... FP chain: nr:4
.....  0: ffffffffffffff80 # PERF_CONTEXT_KERNEL mark
.....  1: ffffffff8116545d
.....  2: ffffffff81167fcc
.....  3: ffffffff813088f4
 ... thread: iperf:595
 ...... dso: /proc/kcore
iperf     595 [002]  9015.616291:     824245  cycles:
        ffffffff8116545d __lock_acquire+0xad ([kernel.kallsyms])
        ffffffff81167fcc lock_acquire+0xcc ([kernel.kallsyms])
        ffffffff813088f4 __bpf_prog_enter+0x34 ([kernel.kallsyms])

After:

... FP chain: nr:44
.....  0: ffffffffffffff80 # PERF_CONTEXT_KERNEL mark
.....  1: ffffffff81165930
.....  2: ffffffff81167fcc
.....  3: ffffffff813088f4
.....  4: ffffffffc000da5e
.....  5: ffffffff81f243df
.....  6: ffffffff81f27326
.....  7: ffffffff81f3a3c3
.....  8: ffffffff81f3c99b
.....  9: ffffffff81ef9870
..... 10: ffffffff81ef9b13
..... 11: ffffffff81ef9c69
..... 12: ffffffff81ef9f47
..... 13: ffffffff81efa15d
..... 14: ffffffff81efa9c0
..... 15: ffffffff81d979eb
..... 16: ffffffff81d987e8
..... 17: ffffffff81ddce16
..... 18: ffffffff81bc7b90
..... 19: ffffffff81bcf677
..... 20: ffffffff81bd1b4f
..... 21: ffffffff81d99693
..... 22: ffffffff81d99a52
..... 23: ffffffff810c9eb2
..... 24: ffffffff810ca631
..... 25: ffffffff822367db
..... 26: ffffffff824015ef
..... 27: ffffffff811678e6
..... 28: ffffffff814f7d85
..... 29: ffffffff814f8119
..... 30: ffffffff81492fb9
..... 31: ffffffff81355c53
..... 32: ffffffff813d79d7
..... 33: ffffffff813d88fc
..... 34: ffffffff8139a52e
..... 35: ffffffff8139a661
..... 36: ffffffff8152c193
..... 37: ffffffff8152cbc5
..... 38: ffffffff814a5908
..... 39: ffffffff814a72d3
..... 40: ffffffff814a758b
..... 41: ffffffff81008869
..... 42: ffffffff822323e8
..... 43: ffffffff8240012f
 ... thread: sleep:493
 ...... dso: /proc/kcore
sleep     493 [000]    55.483168:     410428  cycles:
        ffffffff81165930 __lock_acquire+0x580 ([kernel.kallsyms])
        ffffffff81167fcc lock_acquire+0xcc ([kernel.kallsyms])
        ffffffff813088f4 __bpf_prog_enter+0x34 ([kernel.kallsyms])
        ffffffffc000da5e bpf_trampoline_bpf_prog_075f577900bac1d2_bpf_cubic_acked+0x3a ([kernel.kallsyms])
        ffffffff81f243df tcp_ack+0xd4f ([kernel.kallsyms])
        ffffffff81f27326 tcp_rcv_established+0x3b6 ([kernel.kallsyms])
        ffffffff81f3a3c3 tcp_v4_do_rcv+0x193 ([kernel.kallsyms])
        ffffffff81f3c99b tcp_v4_rcv+0x11fb ([kernel.kallsyms])
        ffffffff81ef9870 ip_protocol_deliver_rcu+0x50 ([kernel.kallsyms])
        ffffffff81ef9b13 ip_local_deliver_finish+0xb3 ([kernel.kallsyms])
        ffffffff81ef9c69 ip_local_deliver+0x79 ([kernel.kallsyms])
        ffffffff81ef9f47 ip_sublist_rcv_finish+0xb7 ([kernel.kallsyms])
        ffffffff81efa15d ip_sublist_rcv+0x18d ([kernel.kallsyms])
        ffffffff81efa9c0 ip_list_rcv+0x110 ([kernel.kallsyms])
        ffffffff81d979eb __netif_receive_skb_list_core+0x21b ([kernel.kallsyms])
        ffffffff81d987e8 netif_receive_skb_list_internal+0x208 ([kernel.kallsyms])
        ffffffff81ddce16 napi_gro_receive+0xf6 ([kernel.kallsyms])
        ffffffff81bc7b90 virtnet_receive_done+0x340 ([kernel.kallsyms])
        ffffffff81bcf677 receive_buf+0xd7 ([kernel.kallsyms])
        ffffffff81bd1b4f virtnet_poll+0xcbf ([kernel.kallsyms])
        ffffffff81d99693 __napi_poll.constprop.0+0x33 ([kernel.kallsyms])
        ffffffff81d99a52 net_rx_action+0x1c2 ([kernel.kallsyms])
        ffffffff810c9eb2 handle_softirqs+0xe2 ([kernel.kallsyms])
        ffffffff810ca631 irq_exit_rcu+0x91 ([kernel.kallsyms])
        ffffffff822367db sysvec_apic_timer_interrupt+0x9b ([kernel.kallsyms])
        ffffffff824015ef asm_sysvec_apic_timer_interrupt+0x1f ([kernel.kallsyms])
        ffffffff811678e6 lock_release+0x186 ([kernel.kallsyms])
        ffffffff814f7d85 prepend_path+0x395 ([kernel.kallsyms])
        ffffffff814f8119 d_path+0x159 ([kernel.kallsyms])
        ffffffff81492fb9 file_path+0x19 ([kernel.kallsyms])
        ffffffff81355c53 perf_event_mmap+0x1e3 ([kernel.kallsyms])
        ffffffff813d79d7 mmap_region+0x2e7 ([kernel.kallsyms])
        ffffffff813d88fc do_mmap+0x4ec ([kernel.kallsyms])
        ffffffff8139a52e vm_mmap_pgoff+0xde ([kernel.kallsyms])
        ffffffff8139a661 vm_mmap+0x31 ([kernel.kallsyms])
        ffffffff8152c193 elf_load+0xa3 ([kernel.kallsyms])
        ffffffff8152cbc5 load_elf_binary+0x655 ([kernel.kallsyms])
        ffffffff814a5908 bprm_execve+0x2a8 ([kernel.kallsyms])
        ffffffff814a72d3 do_execveat_common.isra.0+0x193 ([kernel.kallsyms])
        ffffffff814a758b __x64_sys_execve+0x3b ([kernel.kallsyms])
        ffffffff81008869 x64_sys_call+0x1399 ([kernel.kallsyms])
        ffffffff822323e8 do_syscall_64+0x68 ([kernel.kallsyms])
        ffffffff8240012f entry_SYSCALL_64_after_hwframe+0x76 ([kernel.kallsyms])

Fixes: 85d33df357b6 ("bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS")
Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
Acked-by: Yonghong Song <yonghong.song@...ux.dev>
---
v2:
Refine the commit message for clarity and fix a test bot warning

v1:
https://lore.kernel.org/bpf/20241030111533.907289-1-xukuohai@huaweicloud.com/
---
 include/linux/bpf.h         |  3 +-
 kernel/bpf/bpf_struct_ops.c | 67 +++++++++++++++++++++++++++++++++++++
 kernel/bpf/dispatcher.c     |  3 +-
 kernel/bpf/trampoline.c     |  9 +++--
 4 files changed, 78 insertions(+), 4 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index c3ba4d475174..46f8d6c1a55c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1402,7 +1402,8 @@ int arch_prepare_bpf_dispatcher(void *image, void *buf, s64 *funcs, int num_func
 void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from,
 				struct bpf_prog *to);
 /* Called only from JIT-enabled code, so there's no need for stubs. */
-void bpf_image_ksym_add(void *data, unsigned int size, struct bpf_ksym *ksym);
+void bpf_image_ksym_init(void *data, unsigned int size, struct bpf_ksym *ksym);
+void bpf_image_ksym_add(struct bpf_ksym *ksym);
 void bpf_image_ksym_del(struct bpf_ksym *ksym);
 void bpf_ksym_add(struct bpf_ksym *ksym);
 void bpf_ksym_del(struct bpf_ksym *ksym);
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index fda3dd2ee984..172a081ed1c3 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -38,6 +38,9 @@ struct bpf_struct_ops_map {
 	 * that stores the func args before calling the bpf_prog.
 	 */
 	void *image_pages[MAX_TRAMP_IMAGE_PAGES];
+	u32 ksyms_cnt;
+	/* ksyms for bpf trampolines */
+	struct bpf_ksym *ksyms;
 	/* The owner moduler's btf. */
 	struct btf *btf;
 	/* uvalue->data stores the kernel struct
@@ -586,6 +589,35 @@ int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks,
 	return 0;
 }
 
+static void bpf_struct_ops_ksym_init(struct bpf_prog *prog, void *image,
+				     unsigned int size, struct bpf_ksym *ksym)
+{
+	int n;
+
+	n = strscpy(ksym->name, "bpf_trampoline_", KSYM_NAME_LEN);
+	strncat(ksym->name + n, prog->aux->ksym.name, KSYM_NAME_LEN - 1 - n);
+	INIT_LIST_HEAD_RCU(&ksym->lnode);
+	bpf_image_ksym_init(image, size, ksym);
+}
+
+static void bpf_struct_ops_map_ksyms_add(struct bpf_struct_ops_map *st_map)
+{
+	struct bpf_ksym *ksym = st_map->ksyms;
+	struct bpf_ksym *end = ksym + st_map->ksyms_cnt;
+
+	while (ksym != end && ksym->start)
+		bpf_image_ksym_add(ksym++);
+}
+
+static void bpf_struct_ops_map_ksyms_del(struct bpf_struct_ops_map *st_map)
+{
+	struct bpf_ksym *ksym = st_map->ksyms;
+	struct bpf_ksym *end = ksym + st_map->ksyms_cnt;
+
+	while (ksym != end && ksym->start)
+		bpf_image_ksym_del(ksym++);
+}
+
 static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 					   void *value, u64 flags)
 {
@@ -601,6 +633,7 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 	int prog_fd, err;
 	u32 i, trampoline_start, image_off = 0;
 	void *cur_image = NULL, *image = NULL;
+	struct bpf_ksym *ksym;
 
 	if (flags)
 		return -EINVAL;
@@ -640,6 +673,7 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 	kdata = &kvalue->data;
 
 	module_type = btf_type_by_id(btf_vmlinux, st_ops_ids[IDX_MODULE_ID]);
+	ksym = st_map->ksyms;
 	for_each_member(i, t, member) {
 		const struct btf_type *mtype, *ptype;
 		struct bpf_prog *prog;
@@ -735,6 +769,11 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 
 		/* put prog_id to udata */
 		*(unsigned long *)(udata + moff) = prog->aux->id;
+
+		/* init ksym for this trampoline */
+		bpf_struct_ops_ksym_init(prog, image + trampoline_start,
+					 image_off - trampoline_start,
+					 ksym++);
 	}
 
 	if (st_ops->validate) {
@@ -790,6 +829,8 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 unlock:
 	kfree(tlinks);
 	mutex_unlock(&st_map->lock);
+	if (!err)
+		bpf_struct_ops_map_ksyms_add(st_map);
 	return err;
 }
 
@@ -883,6 +924,10 @@ static void bpf_struct_ops_map_free(struct bpf_map *map)
 	 */
 	synchronize_rcu_mult(call_rcu, call_rcu_tasks);
 
+	/* no trampoline in the map is running anymore, delete symbols */
+	bpf_struct_ops_map_ksyms_del(st_map);
+	synchronize_rcu();
+
 	__bpf_struct_ops_map_free(map);
 }
 
@@ -895,6 +940,19 @@ static int bpf_struct_ops_map_alloc_check(union bpf_attr *attr)
 	return 0;
 }
 
+static u32 count_func_ptrs(const struct btf *btf, const struct btf_type *t)
+{
+	int i;
+	u32 count;
+	const struct btf_member *member;
+
+	count = 0;
+	for_each_member(i, t, member)
+		if (btf_type_resolve_func_ptr(btf, member->type, NULL))
+			count++;
+	return count;
+}
+
 static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 {
 	const struct bpf_struct_ops_desc *st_ops_desc;
@@ -905,6 +963,8 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 	struct bpf_map *map;
 	struct btf *btf;
 	int ret;
+	size_t ksyms_offset;
+	u32 ksyms_cnt;
 
 	if (attr->map_flags & BPF_F_VTYPE_BTF_OBJ_FD) {
 		/* The map holds btf for its whole life time. */
@@ -951,6 +1011,11 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 		 */
 		(vt->size - sizeof(struct bpf_struct_ops_value));
 
+	st_map_size = round_up(st_map_size, sizeof(struct bpf_ksym));
+	ksyms_offset = st_map_size;
+	ksyms_cnt = count_func_ptrs(btf, t);
+	st_map_size += ksyms_cnt * sizeof(struct bpf_ksym);
+
 	st_map = bpf_map_area_alloc(st_map_size, NUMA_NO_NODE);
 	if (!st_map) {
 		ret = -ENOMEM;
@@ -958,6 +1023,8 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 	}
 
 	st_map->st_ops_desc = st_ops_desc;
+	st_map->ksyms = (void *)st_map + ksyms_offset;
+	st_map->ksyms_cnt = ksyms_cnt;
 	map = &st_map->map;
 
 	st_map->uvalue = bpf_map_area_alloc(vt->size, NUMA_NO_NODE);
diff --git a/kernel/bpf/dispatcher.c b/kernel/bpf/dispatcher.c
index 70fb82bf1637..b77db7413f8c 100644
--- a/kernel/bpf/dispatcher.c
+++ b/kernel/bpf/dispatcher.c
@@ -154,7 +154,8 @@ void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from,
 			d->image = NULL;
 			goto out;
 		}
-		bpf_image_ksym_add(d->image, PAGE_SIZE, &d->ksym);
+		bpf_image_ksym_init(d->image, PAGE_SIZE, &d->ksym);
+		bpf_image_ksym_add(&d->ksym);
 	}
 
 	prev_num_progs = d->num_progs;
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 9f36c049f4c2..ecdd2660561f 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -115,10 +115,14 @@ bool bpf_prog_has_trampoline(const struct bpf_prog *prog)
 		(ptype == BPF_PROG_TYPE_LSM && eatype == BPF_LSM_MAC);
 }
 
-void bpf_image_ksym_add(void *data, unsigned int size, struct bpf_ksym *ksym)
+void bpf_image_ksym_init(void *data, unsigned int size, struct bpf_ksym *ksym)
 {
 	ksym->start = (unsigned long) data;
 	ksym->end = ksym->start + size;
+}
+
+void bpf_image_ksym_add(struct bpf_ksym *ksym)
+{
 	bpf_ksym_add(ksym);
 	perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
 			   PAGE_SIZE, false, ksym->name);
@@ -377,7 +381,8 @@ static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, int size)
 	ksym = &im->ksym;
 	INIT_LIST_HEAD_RCU(&ksym->lnode);
 	snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu", key);
-	bpf_image_ksym_add(image, size, ksym);
+	bpf_image_ksym_init(image, size, ksym);
+	bpf_image_ksym_add(ksym);
 	return im;
 
 out_free_image:
-- 
2.39.5

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