From: Intel-wired-lan <redacted> On Behalf Of
Maciej Fijalkowski
Sent: Tuesday, October 26, 2021 10:17 PM
To: intel-wired-lan@lists.osuosl.org
Cc: Lobakin, Alexandr <redacted>;
netdev@vger.kernel.org; Plantykow, Marta A
[off-list ref]; kuba@kernel.org; bpf@vger.kernel.org;
davem@davemloft.net; Karlsson, Magnus [off-list ref]
Subject: [Intel-wired-lan] [PATCH intel-next 2/2] ice: avoid bpf_prog refcount
underflow

From: Marta Plantykow <redacted>

Ice driver has the routines for managing XDP resources that are shared
between ndo_bpf op and VSI rebuild flow. The latter takes place for example
when user changes queue count on an interface via ethtool's set_channels().

There is an issue around the bpf_prog refcounting when VSI is being rebuilt -
since ice_prepare_xdp_rings() is called with vsi->xdp_prog as an argument
that is used later on by ice_vsi_assign_bpf_prog(), same bpf_prog pointers
are swapped with each other. Then it is also interpreted as an 'old_prog'
which in turn causes us to call bpf_prog_put on it that will decrement its
refcount.

Below splat can be interpreted in a way that due to zero refcount of a
bpf_prog it is wiped out from the system while kernel still tries to refer to it:

[  481.069429] BUG: unable to handle page fault for address:
ffffc9000640f038 [  481.077390] #PF: supervisor read access in kernel mode [
481.083335] #PF: error_code(0x0000) - not-present page [  481.089276] PGD
100000067 P4D 100000067 PUD 1001cb067 PMD 106d2b067 PTE 0 [
481.097141] Oops: 0000 [#1] PREEMPT SMP PTI
[  481.101980] CPU: 12 PID: 3339 Comm: sudo Tainted: G           OE     5.15.0-
rc5+ #1
[  481.110840] Hardware name: Intel Corp. GRANTLEY/GRANTLEY, BIOS
GRRFCRB1.86B.0276.D07.1605190235 05/19/2016 [  481.122021] RIP:
0010:dev_xdp_prog_id+0x25/0x40 [  481.127265] Code: 80 00 00 00 00 0f 1f
44 00 00 89 f6 48 c1 e6 04 48 01 fe 48 8b 86 98 08 00 00 48 85 c0 74 13 48 8b
50 18 31 c0 48 85 d2 74 07 <48> 8b 42 38 8b 40 20 c3 48 8b 96 90 08 00 00 eb
e8 66 2e 0f 1f 84 [  481.148991] RSP: 0018:ffffc90007b63868 EFLAGS:
00010286 [  481.155034] RAX: 0000000000000000 RBX: ffff889080824000
RCX: 0000000000000000 [  481.163278] RDX: ffffc9000640f000 RSI:
ffff889080824010 RDI: ffff889080824000 [  481.171527] RBP:
ffff888107af7d00 R08: 0000000000000000 R09: ffff88810db5f6e0 [
481.179776] R10: 0000000000000000 R11: ffff8890885b9988 R12:
ffff88810db5f4bc [  481.188026] R13: 0000000000000000 R14:
0000000000000000 R15: 0000000000000000 [  481.196276] FS:
00007f5466d5bec0(0000) GS:ffff88903fb00000(0000)
knlGS:0000000000000000 [  481.205633] CS:  0010 DS: 0000 ES: 0000 CR0:
0000000080050033 [  481.212279] CR2: ffffc9000640f038 CR3:
000000014429c006 CR4: 00000000003706e0 [  481.220530] DR0:
0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [
481.228771] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400 [  481.237029] Call Trace:
[  481.239856]  rtnl_fill_ifinfo+0x768/0x12e0 [  481.244602]
rtnl_dump_ifinfo+0x525/0x650 [  481.249246]  ? __alloc_skb+0xa5/0x280 [
481.253484]  netlink_dump+0x168/0x3c0 [  481.257725]
netlink_recvmsg+0x21e/0x3e0 [  481.262263]  ____sys_recvmsg+0x87/0x170
[  481.266707]  ? __might_fault+0x20/0x30 [  481.271046]  ?
_copy_from_user+0x66/0xa0 [  481.275591]  ? iovec_from_user+0xf6/0x1c0 [
481.280226]  ___sys_recvmsg+0x82/0x100 [  481.284566]  ?
sock_sendmsg+0x5e/0x60 [  481.288791]  ? __sys_sendto+0xee/0x150 [
481.293129]  __sys_recvmsg+0x56/0xa0 [  481.297267]
do_syscall_64+0x3b/0xc0 [  481.301395]
entry_SYSCALL_64_after_hwframe+0x44/0xae
[  481.307238] RIP: 0033:0x7f5466f39617
[  481.311373] Code: 0c 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb bd 0f 1f 00 f3 0f
1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2f 00 00 00 0f 05 <48> 3d 00 f0 ff
ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10 [  481.342944] RSP:
002b:00007ffedc7f4308 EFLAGS: 00000246 ORIG_RAX: 000000000000002f [
481.361783] RAX: ffffffffffffffda RBX: 00007ffedc7f5460 RCX:
00007f5466f39617 [  481.380278] RDX: 0000000000000000 RSI:
00007ffedc7f5360 RDI: 0000000000000003 [  481.398500] RBP:
00007ffedc7f53f0 R08: 0000000000000000 R09: 000055d556f04d50 [
481.416463] R10: 0000000000000077 R11: 0000000000000246 R12:
00007ffedc7f5360 [  481.434131] R13: 00007ffedc7f5350 R14:
00007ffedc7f5344 R15: 0000000000000e98 [  481.451520] Modules linked in:
ice(OE) af_packet binfmt_misc nls_iso8859_1 ipmi_ssif intel_rapl_msr
intel_rapl_common x86_pkg_temp_thermal intel_powerclamp mxm_wmi
mei_me coretemp mei ipmi_si ipmi_msghandler wmi acpi_pad
acpi_power_meter ip_tables x_tables autofs4 crct10dif_pclmul crc32_pclmul
ghash_clmulni_intel aesni_intel ahci crypto_simd cryptd libahci lpc_ich [last
unloaded: ice] [  481.528558] CR2: ffffc9000640f038 [  481.542041] ---[ end
trace d1f24c9ecf5b61c1 ]---

Fix this by only calling ice_vsi_assign_bpf_prog() inside
ice_prepare_xdp_rings() when current vsi->xdp_prog pointer is NULL.
This way set_channels() flow will not attempt to swap the vsi->xdp_prog
pointers with itself.

Also, sprinkle around some comments that provide a reasoning about
correlation between driver and kernel in terms of bpf_prog refcount.

Fixes: efc2214b6047 ("ice: Add support for XDP")
Reviewed-by: Alexander Lobakin <redacted>
Signed-off-by: Marta Plantykow <redacted> [ Maciej:
don't assign the prog if already present, expand commit
  message ]
Co-developed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
 drivers/net/ethernet/intel/ice/ice_main.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

Tested-by: Kiran Bhandare <redacted>  A Contingent Worker at Intel