Re: [PATCH] Platform lockdown information in SYSFS
From: Daniel Gutson
Date: Tue Aug 04 2020 - 13:37:16 EST
On Tue, Aug 4, 2020 at 1:42 PM Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Tue, Aug 04, 2020 at 11:37:02AM -0300, Daniel Gutson wrote:
> > static void mypci_remove(struct pci_dev *pdev)
> > {
> > /*
> > I tried enabling and disabling this
> > if (child_device != NULL) {
> > put_device(child_device);
> > device_unregister(child_device);
> > }
> > */
>
> You can just call device_destroy() here, but this should be the same.
There's a key difference:
void device_destroy(struct class *class, dev_t devt)
{
struct device *dev;
dev = class_find_device_by_devt(class, devt);
if (dev) {
put_device(dev);
device_unregister(dev);
}
}
It won't work because it receives a dev_t, which in my case is 0,0 and
won't find it.
>
> But, if you have it commented out, that's not good, you have to clean
> this up.
>
> > class_remove_file(&my_class, &class_attr_howareyou);
>
> You don't always have to remove files you create, but it doesn't hurt.
>
> > class_unregister(&my_class);
>
> class_destroy()? But this is the same as well, so all is good.
>
> Try running without the above code commented out.
kaboom :) Seems the reference counting went negative
[ 514.412418] kernfs: can not remove 'uevent', no directory
[ 514.412425] WARNING: CPU: 6 PID: 6203 at fs/kernfs/dir.c:1507
kernfs_remove_by_name_ns+0x8a/0xa0
[ 514.412425] Modules linked in: firmware_security_class(OE-) xxx
[ 514.412458] CPU: 6 PID: 6203 Comm: rmmod Tainted: G OE
5.8.0+ #1
[ 514.412458] Hardware name: xxx
[ 514.412459] RIP: 0010:kernfs_remove_by_name_ns+0x8a/0xa0
[ 514.412460] Code: 00 31 c0 41 5c 41 5d 41 5e 5d c3 48 c7 c7 80 14
93 b1 e8 19 b0 77 00 b8 fe ff ff ff eb e5 48 c7 c7 f8 56 5d b1 e8 3b
ca ce ff <0f> 0b b8 fe ff ff ff eb d0 66 66 2e 0f 1f 84 00 00 00 00 00
66 90
[ 514.412460] RSP: 0018:ffffbedac1a43d48 EFLAGS: 00010286
[ 514.412461] RAX: 0000000000000000 RBX: ffffa081de519c00 RCX: 0000000000000027
[ 514.412461] RDX: 0000000000000027 RSI: 0000000000000082 RDI: ffffa0823d798cc8
[ 514.412462] RBP: ffffbedac1a43d60 R08: 000000000000050e R09: 0000000000000004
[ 514.412462] R10: 0000000000000000 R11: 0000000000000001 R12: ffffa082384650b0
[ 514.412462] R13: ffffffffb15f9575 R14: dead000000000122 R15: dead000000000100
[ 514.412463] FS: 00007f912a4f6540(0000) GS:ffffa0823d780000(0000)
knlGS:0000000000000000
[ 514.412464] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 514.412464] CR2: 0000559b849611b8 CR3: 000000080650e001 CR4: 00000000003606e0
[ 514.412464] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 514.412465] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 514.412465] Call Trace:
[ 514.412468] sysfs_remove_file_ns+0x15/0x20
[ 514.412470] device_del+0x164/0x3e0
[ 514.412472] device_unregister+0x1b/0x60
[ 514.412473] mypci_remove+0x26/0x50 [firmware_security_class]
[ 514.412475] pci_device_remove+0x3e/0xb0
[ 514.412476] device_release_driver_internal+0xf0/0x1c0
[ 514.412477] driver_detach+0x4c/0x8f
[ 514.412477] bus_remove_driver+0x5c/0xd0
[ 514.412478] driver_unregister+0x31/0x50
[ 514.412479] pci_unregister_driver+0x40/0x90
[ 514.412480] my_pci_driver_exit+0x10/0xe80 [firmware_security_class]
[ 514.412482] __x64_sys_delete_module+0x146/0x2a0
[ 514.412483] ? __syscall_return_slowpath+0x31/0x160
[ 514.412485] do_syscall_64+0x52/0xc0
[ 514.412486] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 514.412487] RIP: 0033:0x7f912a642a3b
[ 514.412488] Code: 73 01 c3 48 8b 0d 55 84 0c 00 f7 d8 64 89 01 48
83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 b0 00 00
00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 25 84 0c 00 f7 d8 64 89
01 48
[ 514.412489] RSP: 002b:00007ffc3e5c6b58 EFLAGS: 00000206 ORIG_RAX:
00000000000000b0
[ 514.412489] RAX: ffffffffffffffda RBX: 0000559b84956770 RCX: 00007f912a642a3b
[ 514.412490] RDX: 000000000000000a RSI: 0000000000000800 RDI: 0000559b849567d8
[ 514.412490] RBP: 00007ffc3e5c6bb8 R08: 0000000000000000 R09: 0000000000000000
[ 514.412491] R10: 00007f912a6beac0 R11: 0000000000000206 R12: 00007ffc3e5c6d90
[ 514.412491] R13: 00007ffc3e5c77ba R14: 0000559b849562a0 R15: 0000559b84956770
[ 514.412492] ---[ end trace 6c3ef2924fc0afa7 ]---
[ 514.412492] ------------[ cut here ]------------
[ 514.412493] kernfs: can not remove 'online', no directory
[ 514.412496] WARNING: CPU: 6 PID: 6203 at fs/kernfs/dir.c:1507
kernfs_remove_by_name_ns+0x8a/0xa0
[ 514.412496] Modules linked in: firmware_security_class(OE-) xxx
[ 514.412513] CPU: 6 PID: 6203 Comm: rmmod Tainted: G W OE
5.8.0+ #1
[ 514.412513] Hardware name: xxx
[ 514.412513] RIP: 0010:kernfs_remove_by_name_ns+0x8a/0xa0
[ 514.412514] Code: 00 31 c0 41 5c 41 5d 41 5e 5d c3 48 c7 c7 80 14
93 b1 e8 19 b0 77 00 b8 fe ff ff ff eb e5 48 c7 c7 f8 56 5d b1 e8 3b
ca ce ff <0f> 0b b8 fe ff ff ff eb d0 66 66 2e 0f 1f 84 00 00 00 00 00
66 90
[ 514.412514] RSP: 0018:ffffbedac1a43d20 EFLAGS: 00010282
[ 514.412515] RAX: 0000000000000000 RBX: ffffffffc0c83120 RCX: 0000000000000027
[ 514.412515] RDX: 0000000000000027 RSI: 0000000000000092 RDI: ffffa0823d798cc8
[ 514.412516] RBP: ffffbedac1a43d38 R08: 000000000000053b R09: 0000000000000004
[ 514.412516] R10: 0000000000000000 R11: 0000000000000001 R12: ffffa081de519c00
[ 514.412516] R13: ffffffffb16650b8 R14: dead000000000122 R15: dead000000000100
[ 514.412517] FS: 00007f912a4f6540(0000) GS:ffffa0823d780000(0000)
knlGS:0000000000000000
[ 514.412517] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 514.412518] CR2: 0000559b849611b8 CR3: 000000080650e001 CR4: 00000000003606e0
[ 514.412518] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 514.412519] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 514.412519] Call Trace:
[ 514.412520] sysfs_remove_file_ns+0x15/0x20
[ 514.412521] device_remove_attrs+0x2f/0x70
[ 514.412521] device_del+0x173/0x3e0
[ 514.412523] device_unregister+0x1b/0x60
[ 514.412523] mypci_remove+0x26/0x50 [firmware_security_class]
[ 514.412524] pci_device_remove+0x3e/0xb0
[ 514.412525] device_release_driver_internal+0xf0/0x1c0
[ 514.412526] driver_detach+0x4c/0x8f
[ 514.412526] bus_remove_driver+0x5c/0xd0
[ 514.412527] driver_unregister+0x31/0x50
[ 514.412528] pci_unregister_driver+0x40/0x90
[ 514.412529] my_pci_driver_exit+0x10/0xe80 [firmware_security_class]
[ 514.412530] __x64_sys_delete_module+0x146/0x2a0
[ 514.412531] ? __syscall_return_slowpath+0x31/0x160
[ 514.412532] do_syscall_64+0x52/0xc0
[ 514.412533] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 514.412533] RIP: 0033:0x7f912a642a3b
[ 514.412534] Code: 73 01 c3 48 8b 0d 55 84 0c 00 f7 d8 64 89 01 48
83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 b0 00 00
00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 25 84 0c 00 f7 d8 64 89
01 48
[ 514.412534] RSP: 002b:00007ffc3e5c6b58 EFLAGS: 00000206 ORIG_RAX:
00000000000000b0
[ 514.412535] RAX: ffffffffffffffda RBX: 0000559b84956770 RCX: 00007f912a642a3b
[ 514.412535] RDX: 000000000000000a RSI: 0000000000000800 RDI: 0000559b849567d8
[ 514.412535] RBP: 00007ffc3e5c6bb8 R08: 0000000000000000 R09: 0000000000000000
[ 514.412536] R10: 00007f912a6beac0 R11: 0000000000000206 R12: 00007ffc3e5c6d90
[ 514.412536] R13: 00007ffc3e5c77ba R14: 0000559b849562a0 R15: 0000559b84956770
[ 514.412537] ---[ end trace 6c3ef2924fc0afa8 ]---
[ 514.412543] ------------[ cut here ]------------
[ 514.412543] refcount_t: underflow; use-after-free.
[ 514.412548] WARNING: CPU: 6 PID: 6203 at lib/refcount.c:28
refcount_warn_saturate+0xae/0xf0
[ 514.412548] Modules linked in: firmware_security_class(OE-) xxx
[ 514.412564] CPU: 6 PID: 6203 Comm: rmmod Tainted: G W OE
5.8.0+ #1
[ 514.412565] Hardware name: xxx
[ 514.412566] RIP: 0010:refcount_warn_saturate+0xae/0xf0
[ 514.412566] Code: 65 0c 2d 01 01 e8 77 0a b4 ff 0f 0b 5d c3 80 3d
52 0c 2d 01 00 75 91 48 c7 c7 40 6b 5f b1 c6 05 42 0c 2d 01 01 e8 57
0a b4 ff <0f> 0b 5d c3 80 3d 30 0c 2d 01 00 0f 85 6d ff ff ff 48 c7 c7
98 6b
[ 514.412566] RSP: 0018:ffffbedac1a43d90 EFLAGS: 00010286
[ 514.412567] RAX: 0000000000000000 RBX: ffffa08238465000 RCX: 0000000000000027
[ 514.412567] RDX: 0000000000000027 RSI: 0000000000000096 RDI: ffffa0823d798cc8
[ 514.412568] RBP: ffffbedac1a43d90 R08: 0000000000000569 R09: 0000000000000004
[ 514.412568] R10: 0000000000000000 R11: 0000000000000001 R12: ffffa081de519c00
[ 514.412568] R13: ffffffffc0c83000 R14: dead000000000122 R15: dead000000000100
[ 514.412569] FS: 00007f912a4f6540(0000) GS:ffffa0823d780000(0000)
knlGS:0000000000000000
[ 514.412569] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 514.412570] CR2: 0000559b849611b8 CR3: 000000080650e001 CR4: 00000000003606e0
[ 514.412570] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 514.412570] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 514.412571] Call Trace:
[ 514.412572] kobject_put+0xf1/0x190
[ 514.412573] device_unregister+0x28/0x60
[ 514.412574] mypci_remove+0x26/0x50 [firmware_security_class]
[ 514.412575] pci_device_remove+0x3e/0xb0
[ 514.412576] device_release_driver_internal+0xf0/0x1c0
[ 514.412577] driver_detach+0x4c/0x8f
[ 514.412577] bus_remove_driver+0x5c/0xd0
[ 514.412578] driver_unregister+0x31/0x50
[ 514.412579] pci_unregister_driver+0x40/0x90
[ 514.412580] my_pci_driver_exit+0x10/0xe80 [firmware_security_class]
[ 514.412581] __x64_sys_delete_module+0x146/0x2a0
[ 514.412582] ? __syscall_return_slowpath+0x31/0x160
[ 514.412583] do_syscall_64+0x52/0xc0
[ 514.412584] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 514.412584] RIP: 0033:0x7f912a642a3b
[ 514.412585] Code: 73 01 c3 48 8b 0d 55 84 0c 00 f7 d8 64 89 01 48
83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 b0 00 00
00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 25 84 0c 00 f7 d8 64 89
01 48
[ 514.412585] RSP: 002b:00007ffc3e5c6b58 EFLAGS: 00000206 ORIG_RAX:
00000000000000b0
[ 514.412586] RAX: ffffffffffffffda RBX: 0000559b84956770 RCX: 00007f912a642a3b
[ 514.412586] RDX: 000000000000000a RSI: 0000000000000800 RDI: 0000559b849567d8
[ 514.412586] RBP: 00007ffc3e5c6bb8 R08: 0000000000000000 R09: 0000000000000000
[ 514.412587] R10: 00007f912a6beac0 R11: 0000000000000206 R12: 00007ffc3e5c6d90
[ 514.412587] R13: 00007ffc3e5c77ba R14: 0000559b849562a0 R15: 0000559b84956770
[ 514.412588] ---[ end trace 6c3ef2924fc0afa9 ]---
>
> greg k-h
--
Daniel Gutson
Argentina Site Director
Enginieering Director
Eclypsium
Below The Surface: Get the latest threat research and insights on
firmware and supply chain threats from the research team at Eclypsium.
https://eclypsium.com/research/#threatreport