On 10/9/2024 12:13 AM, Leon Hwang wrote:
This patch prevents an infinite loop issue caused by combination of tailcall
and freplace.
For example:
tc_bpf2bpf.c:
// SPDX-License-Identifier: GPL-2.0
\#include <linux/bpf.h>
\#include <bpf/bpf_helpers.h>
__noinline
int subprog_tc(struct __sk_buff *skb)
{
return skb->len * 2;
}
SEC("tc")
int entry_tc(struct __sk_buff *skb)
{
return subprog_tc(skb);
}
char __license[] SEC("license") = "GPL";
tailcall_freplace.c:
// SPDX-License-Identifier: GPL-2.0
\#include <linux/bpf.h>
\#include <bpf/bpf_helpers.h>
struct {
__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
__uint(max_entries, 1);
__uint(key_size, sizeof(__u32));
__uint(value_size, sizeof(__u32));
} jmp_table SEC(".maps");
int count = 0;
SEC("freplace")
int entry_freplace(struct __sk_buff *skb)
{
count++;
bpf_tail_call_static(skb, &jmp_table, 0);
return count;
}
char __license[] SEC("license") = "GPL";
The attach target of entry_freplace is subprog_tc, and the tail callee
in entry_freplace is entry_tc.
Then, the infinite loop will be entry_tc -> subprog_tc -> entry_freplace
--tailcall-> entry_tc, because tail_call_cnt in entry_freplace will count
from zero for every time of entry_freplace execution. Kernel will panic,
like:
[ 15.310490] BUG: TASK stack guard page was hit at (____ptrval____)
(stack is (____ptrval____)..(____ptrval____))
[ 15.310490] Oops: stack guard page: 0000 [#1] PREEMPT SMP NOPTI
[ 15.310490] CPU: 1 PID: 89 Comm: test_progs Tainted: G OE
6.10.0-rc6-g026dcdae8d3e-dirty #72
[ 15.310490] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX,
1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 15.310490] RIP: 0010:bpf_prog_3a140cef239a4b4f_subprog_tail+0x14/0x53
[ 15.310490] Code: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
cc cc cc cc cc f3 0f 1e fa 0f 1f 44 00 00 0f 1f 00 55 48 89 e5 f3 0f 1e
fa <50> 50 53 41 55 48 89 fb 49 bd 00 2a 46 82 98 9c ff ff 48 89 df 4c
[ 15.310490] RSP: 0018:ffffb500c0aa0000 EFLAGS: 00000202
[ 15.310490] RAX: ffffb500c0aa0028 RBX: ffff9c98808b7e00 RCX:
0000000000008cb5
[ 15.310490] RDX: 0000000000000000 RSI: ffff9c9882462a00 RDI:
ffff9c98808b7e00
[ 15.310490] RBP: ffffb500c0aa0000 R08: 0000000000000000 R09:
0000000000000000
[ 15.310490] R10: 0000000000000001 R11: 0000000000000000 R12:
ffffb500c01af000
[ 15.310490] R13: ffffb500c01cd000 R14: 0000000000000000 R15:
0000000000000000
[ 15.310490] FS: 00007f133b665140(0000) GS:ffff9c98bbd00000(0000)
knlGS:0000000000000000
[ 15.310490] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 15.310490] CR2: ffffb500c0a9fff8 CR3: 0000000102478000 CR4:
00000000000006f0
[ 15.310490] Call Trace:
[ 15.310490] <#DF>
[ 15.310490] ? die+0x36/0x90
[ 15.310490] ? handle_stack_overflow+0x4d/0x60
[ 15.310490] ? exc_double_fault+0x117/0x1a0
[ 15.310490] ? asm_exc_double_fault+0x23/0x30
[ 15.310490] ? bpf_prog_3a140cef239a4b4f_subprog_tail+0x14/0x53
[ 15.310490] </#DF>
[ 15.310490] <TASK>
[ 15.310490] bpf_prog_85781a698094722f_entry+0x4c/0x64
[ 15.310490] bpf_prog_1c515f389a9059b4_entry2+0x19/0x1b
[ 15.310490] ...
[ 15.310490] bpf_prog_85781a698094722f_entry+0x4c/0x64
[ 15.310490] bpf_prog_1c515f389a9059b4_entry2+0x19/0x1b
[ 15.310490] bpf_test_run+0x210/0x370
[ 15.310490] ? bpf_test_run+0x128/0x370
[ 15.310490] bpf_prog_test_run_skb+0x388/0x7a0
[ 15.310490] __sys_bpf+0xdbf/0x2c40
[ 15.310490] ? clockevents_program_event+0x52/0xf0
[ 15.310490] ? lock_release+0xbf/0x290
[ 15.310490] __x64_sys_bpf+0x1e/0x30
[ 15.310490] do_syscall_64+0x68/0x140
[ 15.310490] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 15.310490] RIP: 0033:0x7f133b52725d
[ 15.310490] Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa
48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f
05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 8b bb 0d 00 f7 d8 64 89 01 48
[ 15.310490] RSP: 002b:00007ffddbc10258 EFLAGS: 00000206 ORIG_RAX:
0000000000000141
[ 15.310490] RAX: ffffffffffffffda RBX: 00007ffddbc10828 RCX:
00007f133b52725d
[ 15.310490] RDX: 0000000000000050 RSI: 00007ffddbc102a0 RDI:
000000000000000a
[ 15.310490] RBP: 00007ffddbc10270 R08: 0000000000000000 R09:
00007ffddbc102a0
[ 15.310490] R10: 0000000000000064 R11: 0000000000000206 R12:
0000000000000004
[ 15.310490] R13: 0000000000000000 R14: 0000558ec4c24890 R15:
00007f133b6ed000
[ 15.310490] </TASK>
[ 15.310490] Modules linked in: bpf_testmod(OE)
[ 15.310490] ---[ end trace 0000000000000000 ]---
[ 15.310490] RIP: 0010:bpf_prog_3a140cef239a4b4f_subprog_tail+0x14/0x53
[ 15.310490] Code: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
cc cc cc cc cc f3 0f 1e fa 0f 1f 44 00 00 0f 1f 00 55 48 89 e5 f3 0f 1e
fa <50> 50 53 41 55 48 89 fb 49 bd 00 2a 46 82 98 9c ff ff 48 89 df 4c
[ 15.310490] RSP: 0018:ffffb500c0aa0000 EFLAGS: 00000202
[ 15.310490] RAX: ffffb500c0aa0028 RBX: ffff9c98808b7e00 RCX:
0000000000008cb5
[ 15.310490] RDX: 0000000000000000 RSI: ffff9c9882462a00 RDI:
ffff9c98808b7e00
[ 15.310490] RBP: ffffb500c0aa0000 R08: 0000000000000000 R09:
0000000000000000
[ 15.310490] R10: 0000000000000001 R11: 0000000000000000 R12:
ffffb500c01af000
[ 15.310490] R13: ffffb500c01cd000 R14: 0000000000000000 R15:
0000000000000000
[ 15.310490] FS: 00007f133b665140(0000) GS:ffff9c98bbd00000(0000)
knlGS:0000000000000000
[ 15.310490] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 15.310490] CR2: ffffb500c0a9fff8 CR3: 0000000102478000 CR4:
00000000000006f0
[ 15.310490] Kernel panic - not syncing: Fatal exception in interrupt
[ 15.310490] Kernel Offset: 0x30000000 from 0xffffffff81000000
(relocation range: 0xffffffff80000000-0xffffffffbfffffff)
This patch prevents this panic by preventing updating extended prog to
prog_array map and preventing extending a prog, which has been updated
to prog_array map, with freplace prog.
If a prog or its subprog has been extended by freplace prog, the prog
can not be updated to prog_array map.
If a prog has been updated to prog_array map, it or its subprog can not
be extended by freplace prog.
BTW, fix a minor code style issue by replacing 8 spaces with a tab.
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202410080455.vy5GT8Vz-lkp@xxxxxxxxx/
Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx>
---
include/linux/bpf.h | 21 ++++++++++++++++++++
kernel/bpf/arraymap.c | 23 +++++++++++++++++++++-
kernel/bpf/core.c | 1 +
kernel/bpf/syscall.c | 21 ++++++++++++++------
kernel/bpf/trampoline.c | 43 +++++++++++++++++++++++++++++++++++++++++
5 files changed, 102 insertions(+), 7 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 19d8ca8ac960f..213a68c59bdf7 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1294,6 +1294,12 @@ bool __bpf_dynptr_is_rdonly(const struct bpf_dynptr_kern *ptr);
#ifdef CONFIG_BPF_JIT
int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr);
int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr);
+int bpf_extension_link_prog(struct bpf_tramp_link *link,
+ struct bpf_trampoline *tr,
+ struct bpf_prog *tgt_prog);
+int bpf_extension_unlink_prog(struct bpf_tramp_link *link,
+ struct bpf_trampoline *tr,
+ struct bpf_prog *tgt_prog);
struct bpf_trampoline *bpf_trampoline_get(u64 key,
struct bpf_attach_target_info *tgt_info);
void bpf_trampoline_put(struct bpf_trampoline *tr);
@@ -1383,6 +1389,18 @@ static inline int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
{
return -ENOTSUPP;
}
+static inline int bpf_extension_link_prog(struct bpf_tramp_link *link,
+ struct bpf_trampoline *tr,
+ struct bpf_prog *tgt_prog)
+{
+ return -ENOTSUPP;
+}
+static inline int bpf_extension_unlink_prog(struct bpf_tramp_link *link,
+ struct bpf_trampoline *tr,
+ struct bpf_prog *tgt_prog)
+{
+ return -ENOTSUPP;
+}
static inline struct bpf_trampoline *bpf_trampoline_get(u64 key,
struct bpf_attach_target_info *tgt_info)
{
@@ -1483,6 +1501,9 @@ struct bpf_prog_aux {
bool xdp_has_frags;
bool exception_cb;
bool exception_boundary;
+ bool is_extended; /* true if extended by freplace program */
+ u64 prog_array_member_cnt; /* counts how many times as member of prog_array */
+ struct mutex ext_mutex; /* mutex for is_extended and prog_array_member_cnt */
struct bpf_arena *arena;
/* BTF_KIND_FUNC_PROTO for valid attach_btf_id */
const struct btf_type *attach_func_proto;
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 79660e3fca4c1..f9bd63a74eee7 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -947,6 +947,7 @@ static void *prog_fd_array_get_ptr(struct bpf_map *map,
struct file *map_file, int fd)
{
struct bpf_prog *prog = bpf_prog_get(fd);
+ bool is_extended;
if (IS_ERR(prog))
return prog;
@@ -956,13 +957,33 @@ static void *prog_fd_array_get_ptr(struct bpf_map *map,
return ERR_PTR(-EINVAL);
}
+ mutex_lock(&prog->aux->ext_mutex);
+ is_extended = prog->aux->is_extended;
+ if (!is_extended)
+ prog->aux->prog_array_member_cnt++;
+ mutex_unlock(&prog->aux->ext_mutex);
+ if (is_extended) {
+ /* Extended prog can not be tail callee. It's to prevent a
+ * potential infinite loop like:
+ * tail callee prog entry -> tail callee prog subprog ->
+ * freplace prog entry --tailcall-> tail callee prog entry.
+ */
+ bpf_prog_put(prog);
+ return ERR_PTR(-EBUSY);
+ }
Sorry for the delay.
IIUC, extension prog should not be tailcalled independently, so an error
should also be returned if prog->type == BPF_PROG_TYPE_EXT
+
return prog;
}
static void prog_fd_array_put_ptr(struct bpf_map *map, void *ptr, bool need_defer)
{
+ struct bpf_prog *prog = ptr;
+
+ mutex_lock(&prog->aux->ext_mutex);
+ prog->aux->prog_array_member_cnt--;
+ mutex_unlock(&prog->aux->ext_mutex);
/* bpf_prog is freed after one RCU or tasks trace grace period */
- bpf_prog_put(ptr);
+ bpf_prog_put(prog);
}
static u32 prog_fd_array_sys_lookup_elem(void *ptr)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 5e77c58e06010..233ea78f8f1bd 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -131,6 +131,7 @@ struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flag
INIT_LIST_HEAD_RCU(&fp->aux->ksym_prefix.lnode);
#endif
mutex_init(&fp->aux->used_maps_mutex);
+ mutex_init(&fp->aux->ext_mutex);
mutex_init(&fp->aux->dst_mutex);
return fp;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index a8f1808a1ca54..4a5a44bbb5f50 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3212,15 +3212,21 @@ static void bpf_tracing_link_release(struct bpf_link *link)
{
struct bpf_tracing_link *tr_link =
container_of(link, struct bpf_tracing_link, link.link);
+ struct bpf_prog *tgt_prog = tr_link->tgt_prog;
- WARN_ON_ONCE(bpf_trampoline_unlink_prog(&tr_link->link,
- tr_link->trampoline));
+ if (link->prog->type == BPF_PROG_TYPE_EXT)
+ WARN_ON_ONCE(bpf_extension_unlink_prog(&tr_link->link,
+ tr_link->trampoline,
+ tgt_prog));
+ else
+ WARN_ON_ONCE(bpf_trampoline_unlink_prog(&tr_link->link,
+ tr_link->trampoline));
bpf_trampoline_put(tr_link->trampoline);
/* tgt_prog is NULL if target is a kernel function */
- if (tr_link->tgt_prog)
- bpf_prog_put(tr_link->tgt_prog);
+ if (tgt_prog)
+ bpf_prog_put(tgt_prog);
}
static void bpf_tracing_link_dealloc(struct bpf_link *link)
@@ -3354,7 +3360,7 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
* in prog->aux
*
* - if prog->aux->dst_trampoline is NULL, the program has already been
- * attached to a target and its initial target was cleared (below)
+ * attached to a target and its initial target was cleared (below)
*
* - if tgt_prog != NULL, the caller specified tgt_prog_fd +
* target_btf_id using the link_create API.
@@ -3429,7 +3435,10 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
if (err)
goto out_unlock;
- err = bpf_trampoline_link_prog(&link->link, tr);
+ if (prog->type == BPF_PROG_TYPE_EXT)
+ err = bpf_extension_link_prog(&link->link, tr, tgt_prog);
+ else
+ err = bpf_trampoline_link_prog(&link->link, tr);
if (err) {
bpf_link_cleanup(&link_primer);
link = NULL;
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index f8302a5ca400d..b14f56046ad4e 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -580,6 +580,35 @@ int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline
return err;
}
+int bpf_extension_link_prog(struct bpf_tramp_link *link,
+ struct bpf_trampoline *tr,
+ struct bpf_prog *tgt_prog)
+{
+ struct bpf_prog_aux *aux = tgt_prog->aux;
+ int err;
+
+ mutex_lock(&aux->ext_mutex);
+ if (aux->prog_array_member_cnt) {
+ /* Program extensions can not extend target prog when the target
+ * prog has been updated to any prog_array map as tail callee.
+ * It's to prevent a potential infinite loop like:
+ * tgt prog entry -> tgt prog subprog -> freplace prog entry
+ * --tailcall-> tgt prog entry.
+ */
+ err = -EBUSY;
+ goto out_unlock;
+ }
+
+ err = bpf_trampoline_link_prog(link, tr);
+ if (err)
+ goto out_unlock;
+
+ aux->is_extended = true;
+out_unlock:
+ mutex_unlock(&aux->ext_mutex);
+ return err;
+}
+
static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr)
{
enum bpf_tramp_prog_type kind;
@@ -609,6 +638,20 @@ int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampolin
return err;
}
+int bpf_extension_unlink_prog(struct bpf_tramp_link *link,
+ struct bpf_trampoline *tr,
+ struct bpf_prog *tgt_prog)
+{
+ struct bpf_prog_aux *aux = tgt_prog->aux;
+ int err;
+
+ mutex_lock(&aux->ext_mutex);
+ err = bpf_trampoline_unlink_prog(link, tr);
+ aux->is_extended = false;
+ mutex_unlock(&aux->ext_mutex);
+ return err;
+}
+
#if defined(CONFIG_CGROUP_BPF) && defined(CONFIG_BPF_LSM)
static void bpf_shim_tramp_link_release(struct bpf_link *link)
{
