[PATCH 5.6 018/194] hv_netvsc: Fix netvsc_start_xmits return type

Greg Kroah-Hartman
2020-05-18T18:00:29Z

From: Nathan Chancellor <natechancellor@gmail.com>

[ Upstream commit 7fdc66debebc6a7170a37c8c9b0d9585a9788fb4 ]

netvsc_start_xmit is used as a callback function for the ndo_start_xmit
function pointer. ndo_start_xmit's return type is netdev_tx_t but
netvsc_start_xmit's return type is int.

This causes a failure with Control Flow Integrity (CFI), which requires
function pointer prototypes and callback function definitions to match
exactly. When CFI is in enforcing, the kernel panics. When booting a
CFI kernel with WSL 2, the VM is immediately terminated because of this.

The splat when CONFIG_CFI_PERMISSIVE is used:

[ 5.916765] CFI failure (target: netvsc_start_xmit+0x0/0x10):
[ 5.916771] WARNING: CPU: 8 PID: 0 at kernel/cfi.c:29 __cfi_check_fail+0x2e/0x40
[ 5.916772] Modules linked in:
[ 5.916774] CPU: 8 PID: 0 Comm: swapper/8 Not tainted 5.7.0-rc3-next-20200424-microsoft-cbl-00001-ged4eb37d2c69-dirty #1
[ 5.916776] RIP: 0010:__cfi_check_fail+0x2e/0x40
[ 5.916777] Code: 48 c7 c7 70 98 63 a9 48 c7 c6 11 db 47 a9 e8 69 55 59 00 85 c0 75 02 5b c3 48 c7 c7 73 c6 43 a9 48 89 de 31 c0 e8 12 2d f0 ff <0f> 0b 5b c3 00 00 cc cc 00 00 cc cc 00 00 cc cc 00 00 85 f6 74 25
[ 5.916778] RSP: 0018:ffffa803c0260b78 EFLAGS: 00010246
[ 5.916779] RAX: 712a1af25779e900 RBX: ffffffffa8cf7950 RCX: ffffffffa962cf08
[ 5.916779] RDX: ffffffffa9c36b60 RSI: 0000000000000082 RDI: ffffffffa9c36b5c
[ 5.916780] RBP: ffff8ffc4779c2c0 R08: 0000000000000001 R09: ffffffffa9c3c300
[ 5.916781] R10: 0000000000000151 R11: ffffffffa9c36b60 R12: ffff8ffe39084000
[ 5.916782] R13: ffffffffa8cf7950 R14: ffffffffa8d12cb0 R15: ffff8ffe39320140
[ 5.916784] FS: 0000000000000000(0000) GS:ffff8ffe3bc00000(0000) knlGS:0000000000000000
[ 5.916785] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 5.916786] CR2: 00007ffef5749408 CR3: 00000002f4f5e000 CR4: 0000000000340ea0
[ 5.916787] Call Trace:
[ 5.916788] <IRQ>
[ 5.916790] __cfi_check+0x3ab58/0x450e0
[ 5.916793] ? dev_hard_start_xmit+0x11f/0x160
[ 5.916795] ? sch_direct_xmit+0xf2/0x230
[ 5.916796] ? __dev_queue_xmit.llvm.11471227737707190958+0x69d/0x8e0
[ 5.916797] ? neigh_resolve_output+0xdf/0x220
[ 5.916799] ? neigh_connected_output.cfi_jt+0x8/0x8
[ 5.916801] ? ip6_finish_output2+0x398/0x4c0
[ 5.916803] ? nf_nat_ipv6_out+0x10/0xa0
[ 5.916804] ? nf_hook_slow+0x84/0x100
[ 5.916807] ? ip6_input_finish+0x8/0x8
[ 5.916807] ? ip6_output+0x6f/0x110
[ 5.916808] ? __ip6_local_out.cfi_jt+0x8/0x8
[ 5.916810] ? mld_sendpack+0x28e/0x330
[ 5.916811] ? ip_rt_bug+0x8/0x8
[ 5.916813] ? mld_ifc_timer_expire+0x2db/0x400
[ 5.916814] ? neigh_proxy_process+0x8/0x8
[ 5.916816] ? call_timer_fn+0x3d/0xd0
[ 5.916817] ? __run_timers+0x2a9/0x300
[ 5.916819] ? rcu_core_si+0x8/0x8
[ 5.916820] ? run_timer_softirq+0x14/0x30
[ 5.916821] ? __do_softirq+0x154/0x262
[ 5.916822] ? native_x2apic_icr_write+0x8/0x8
[ 5.916824] ? irq_exit+0xba/0xc0
[ 5.916825] ? hv_stimer0_vector_handler+0x99/0xe0
[ 5.916826] ? hv_stimer0_callback_vector+0xf/0x20
[ 5.916826] </IRQ>
[ 5.916828] ? hv_stimer_global_cleanup.cfi_jt+0x8/0x8
[ 5.916829] ? raw_setsockopt+0x8/0x8
[ 5.916830] ? default_idle+0xe/0x10
[ 5.916832] ? do_idle.llvm.10446269078108580492+0xb7/0x130
[ 5.916833] ? raw_setsockopt+0x8/0x8
[ 5.916833] ? cpu_startup_entry+0x15/0x20
[ 5.916835] ? cpu_hotplug_enable.cfi_jt+0x8/0x8
[ 5.916836] ? start_secondary+0x188/0x190
[ 5.916837] ? secondary_startup_64+0xa5/0xb0
[ 5.916838] ---[ end trace f2683fa869597ba5 ]---

Avoid this by using the right return type for netvsc_start_xmit.

Fixes: fceaf24a943d8 ("Staging: hv: add the Hyper-V virtual network driver")
Link: https://github.com/ClangBuiltLinux/linux/issues/1009
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/hyperv/netvsc_drv.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 2c0a24c606fc7..28a5d46ad5266 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -710,7 +710,8 @@ static int netvsc_xmit(struct sk_buff *skb, struct net_device *net, bool xdp_tx)
goto drop;
}

-static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *ndev)
+static netdev_tx_t netvsc_start_xmit(struct sk_buff *skb,
+ struct net_device *ndev)
{
return netvsc_xmit(skb, ndev, false);
}
--
2.20.1