[PATCH bpf v3 0/2] bpf: prevent offloaded programs from running on host via tcx/netkit

Jiayuan Chen
2026-04-25T11:00:11Z

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already been replaced by bpf_prog_warn_on_exec() during offload compile,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, netkit and bpf_xdp_link_update() can install an
offloaded program onto a software execution path without rejecting it.
Rather than sprinkling the same check across every attach/update entry
point, do it at the source:

- bpf_mprog_attach() is the single chokepoint for tcx/netkit (covers
all three of attach, link create and link update on both subsystems,
six call sites in total).
- dev_xdp_install() is the single chokepoint for XDP (covers both the
dev_xdp_attach() path and the bpf_xdp_link_update() path which
previously bypassed the check).

This series adds/moves the check into those two functions so offloaded
programs can no longer be attached to (or swapped into) the software
path, regardless of which entry point is used.

v2 -> v3:
- Alexei suggested converging the check rather than spreading it
across attach entry points. Consolidated into a single check at
bpf_mprog_attach() (covers all six tcx/netkit paths) and moved the
existing XDP check from dev_xdp_attach() into dev_xdp_install() so
the bpf_xdp_link_update() path is also covered. Three patches
collapse into two.
v2: https://lore.kernel.org/bpf/20260424104201.217604-1-jiayuan.chen@linux.dev/

v1 -> v2:
- tcx/netkit: also reject offloaded progs in the link update callback
(tcx_link_update/netkit_link_update), not just attach; pointed out
by the AI review on v1.
- Add patch 3/3 for the same hole in bpf_xdp_link_update().
v1: https://lore.kernel.org/bpf/20260423033609.252464-1-jiayuan.chen@linux.dev/

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

Jiayuan Chen (2):
bpf, tcx, netkit: reject offloaded programs
bpf, xdp: move offload check into dev_xdp_install()

kernel/bpf/mprog.c | 11 +++++++++++
net/core/dev.c | 9 +++++----
2 files changed, 16 insertions(+), 4 deletions(-)

--
2.43.0