[PATCH bpf 0/2] bpf: prevent offloaded programs from running on host via tcx/netkit

[PATCH bpf 0/2] bpf: prevent offloaded programs from running on host via tcx/netkit

[Jiayuan Chen]

Yinhao reported a splat [1] when attaching a BPF program loaded with
prog_ifindex (targeted at an offload-capable device such as netdevsim)
to the software path via BPF_TCX_EGRESS. The program's bpf_func had
already been replaced by bpf_prog_warn_on_exec() during offload compile,
so the first packet that reaches tcx_run() trips the WARN:

[   19.592982] ------------[ cut here ]------------
[   19.594654] attempt to execute device eBPF program on the host!
[   19.594659] WARNING: kernel/bpf/offload.c:420 at 0x0, CPU#0: poc/337
[   19.599906] Modules linked in:
[   19.600680] CPU: 0 UID: 0 PID: 337 Comm: poc Not tainted
6.18.0-rc7-next-20251125 #10 PREEMPT(none)
[   19.601659] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX,
1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[   19.602684] RIP: 0010:bpf_prog_warn_on_exec+0xc/0x20
[   19.603241] Code: 28 00 48 89 ef e8 74 44 2f 00 eb d7 66 90 90 90 90
90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 48 8d 3d a4 eb 95
06 <67> 48 0f b9 3a 31 c0 e9 83 76 44 ff 0f 1f 84 00 00 00 00 00 90 90
[   19.605093] RSP: 0018:ffff8881066e73d8 EFLAGS: 00010246
[   19.605663] RAX: ffffffff81cbca70 RBX: ffff8881013c4210 RCX:
0000000000000004
[   19.606378] RDX: 1ffff11020278842 RSI: ffffc90000563060 RDI:
ffffffff8861b620
[   19.607107] RBP: ffff8881010d0640 R08: ffff8881013c4210 R09:
ffff8881010d06b0
[   19.607827] R10: ffff8881010d06c3 R11: ffffc90000563000 R12:
ffffc90000563000
[   19.608751] R13: ffff8881010d06b4 R14: ffff888115eb1a34 R15:
dffffc0000000000
[   19.609478] FS:  000000000294c380(0000) GS:ffff8881911e9000(0000)
knlGS:0000000000000000
[   19.610316] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   19.610943] CR2: 000057f6b9eb38c0 CR3: 00000001010ea000 CR4:
0000000000750ef0
[   19.611712] PKRU: 55555554
[   19.612006] Call Trace:
[   19.612281]  <TASK>
[   19.612523]  __dev_queue_xmit+0x22cb/0x3530
[   19.617607]  ip_finish_output2+0x621/0x1a60
[   19.621371]  ip_output+0x170/0x2e0
[   19.624586]  ip_send_skb+0x129/0x180
[   19.624940]  udp_send_skb+0x65d/0x1300
[   19.625316]  udp_sendmsg+0x13bf/0x2000
[   19.629960]  __sys_sendto+0x396/0x470
[   19.633720]  __x64_sys_sendto+0xdc/0x1b0
[   19.635066]  do_syscall_64+0x76/0x10a0
[   19.641701]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[   19.642240] RIP: 0033:0x4240d7
[   19.642597] Code: 00 89 01 e9 c1 fe ff ff e8 f6 03 00 00 66 0f 1f 44
00 00 f3 0f 1e fa 80 3d 8d 3f 09 00 00 41 89 ca 74 10 b8 2c 00 00 00 0f
05 <48> 3d 00 f0 ff ff 77 69 c3 55 48 89 e5 53 48 83 ec 38 44 89 4d d0
[   19.646088] RSP: 002b:00007fffcb9ecb68 EFLAGS: 00000202 ORIG_RAX:
000000000000002c
[   19.648938] RAX: ffffffffffffffda RBX: 0000000000000001 RCX:
00000000004240d7
[   19.652116] RDX: 0000000000000008 RSI: 00007fffcb9ecce0 RDI:
0000000000000005
[   19.653148] RBP: 00007fffcb9eccf0 R08: 00007fffcb9ecbb0 R09:
0000000000000010
[   19.653951] R10: 0000000000000000 R11: 0000000000000202 R12:
00007fffcb9ece08
[   19.654760] R13: 00007fffcb9ece18 R14: 00000000004b2868 R15:
0000000000000001
[   19.657462]  </TASK>
[   19.657703] ---[ end trace 0000000000000000 ]---

The reason is that tcx and netkit never checked for offloaded programs
on attach, unlike XDP which already rejects this in dev_xdp_attach().
This series adds the same guard to both so offloaded programs can't be
attached to the software path.

[1]: https://lore.kernel.org/bpf/64d8e2b5-a214-4f3c-b9e8-bcedbcb2c602@hust.edu.cn/

Jiayuan Chen (2):
  bpf, tcx: reject offloaded programs on attach
  bpf, netkit: reject offloaded programs on attach

 drivers/net/netkit.c | 6 ++++++
 kernel/bpf/tcx.c     | 6 ++++++
 2 files changed, 12 insertions(+)

-- 
2.43.0

[PATCH bpf 1/2] bpf, tcx: reject offloaded programs on attach

[Jiayuan Chen]

An offloaded prog's bpf_func is replaced by bpf_prog_warn_on_exec(),
since it's supposed to run on the NIC, not the host. But tcx doesn't
check this and happily attaches it to the software path, so the first
packet hits the WARN.

XDP already guards this in dev_xdp_attach(); tcx just never got the
same check. Add it to both tcx_prog_attach() and tcx_link_attach().

Use bpf_prog_is_offloaded() instead of bpf_prog_is_dev_bound() so that
dev-bound-only programs (still JITed for host) keep working.

Fixes: e420bed025071 ("bpf: Add fd-based tcx multi-prog infra with link support")
Reported-by: Yinhao Hu <dddddd@hust.edu.cn>
Reported-by: Kaiyan Mei <M202472210@hust.edu.cn>
Reported-by: Dongliang Mu <dzm91@hust.edu.cn>
Closes: https://lore.kernel.org/bpf/64d8e2b5-a214-4f3c-b9e8-bcedbcb2c602@hust.edu.cn/
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
 kernel/bpf/tcx.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/bpf/tcx.c b/kernel/bpf/tcx.c
index 02db0113b8e7c..86f4636d5a677 100644
--- a/kernel/bpf/tcx.c
+++ b/kernel/bpf/tcx.c
@@ -16,6 +16,9 @@ int tcx_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 	struct net_device *dev;
 	int ret;
 
+	if (bpf_prog_is_offloaded(prog->aux))
+		return -EINVAL;
+
 	rtnl_lock();
 	dev = __dev_get_by_index(net, attr->target_ifindex);
 	if (!dev) {
@@ -315,6 +318,9 @@ int tcx_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 	struct tcx_link *tcx;
 	int ret;
 
+	if (bpf_prog_is_offloaded(prog->aux))
+		return -EINVAL;
+
 	rtnl_lock();
 	dev = __dev_get_by_index(net, attr->link_create.target_ifindex);
 	if (!dev) {
-- 
2.43.0

[PATCH bpf 2/2] bpf, netkit: reject offloaded programs on attach

[Jiayuan Chen]

Same issue as the tcx fix: netkit accepts SCHED_CLS programs but never
checks if they were loaded for hardware offload. If someone loads a
program with prog_ifindex pointing to an offload-capable device and then
attaches it to a netkit peer, the bpf_func is bpf_prog_warn_on_exec()
and the first packet triggers the WARN.

Reject offloaded programs in both netkit_prog_attach() and
netkit_link_attach().

Fixes: 35dfaad7188cd ("netkit, bpf: Add bpf programmable net device")
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
 drivers/net/netkit.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/netkit.c b/drivers/net/netkit.c
index 5c0e01396e064..c4f764034c90f 100644
--- a/drivers/net/netkit.c
+++ b/drivers/net/netkit.c
@@ -533,6 +533,9 @@ int netkit_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 	struct net_device *dev;
 	int ret;
 
+	if (bpf_prog_is_offloaded(prog->aux))
+		return -EINVAL;
+
 	rtnl_lock();
 	dev = netkit_dev_fetch(current->nsproxy->net_ns, attr->target_ifindex,
 			       attr->attach_type);
@@ -788,6 +791,9 @@ int netkit_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 	struct net_device *dev;
 	int ret;
 
+	if (bpf_prog_is_offloaded(prog->aux))
+		return -EINVAL;
+
 	rtnl_lock();
 	dev = netkit_dev_fetch(current->nsproxy->net_ns,
 			       attr->link_create.target_ifindex,
-- 
2.43.0