[PATCH v5 3/4] LSM: Define SELinux function to measure state and policy

Mon Aug 3 21:07:24 UTC 2020

On 8/3/20 4:37 PM, Lakshmi Ramasubramanian wrote:

> On 8/3/20 1:29 PM, Stephen Smalley wrote:
>> On 8/3/20 4:00 PM, Stephen Smalley wrote:
>>
>>> On Mon, Aug 3, 2020 at 12:14 PM Lakshmi Ramasubramanian
>>> <nramas at linux.microsoft.com> wrote:
>>>> On 8/3/20 8:11 AM, Stephen Smalley wrote:
>>>>> Possibly I'm missing something but with these patches applied on 
>>>>> top of
>>>>> next-integrity, and the following lines added to /etc/ima/ima-policy:
>>>>>
>>>>> measure func=LSM_STATE template=ima-buf
>>>>> measure func=LSM_POLICY
>>>>>
>>>>> I still don't get the selinux-state or selinux-policy-hash entries in
>>>>> the ascii_runtime_measurements file.  No errors during loading of the
>>>>> ima policy as far as I can see.
>>>>>
>>>> Could you please check if the following config is set?
>>>> CONFIG_IMA_QUEUE_EARLY_BOOT_DATA=y
>>> Yes, I have that set.
>>>
>>>> Try changing /sys/fs/selinux/checkreqprot and check
>>>> ascii_runtime_measurements file again?
>>> No change.  Likewise for changing enforce or running load_policy again.
>>>
>>>> Also, could you please check if
>>>> /sys/kernel/security/integrity/ima/policy contains LSM_STATE and
>>>> LSM_POLICY entries?
>>> Yes, it does.  However, I noticed that if I reduce the policy to only
>>> contain those entries and no others and reboot, then I get
>>> measurements.  Whereas if I append them to an existing policy like the
>>> one below, they seem to be ignored:
>>> dont_measure fsmagic=0x9fa0
>>> dont_measure fsmagic=0x62656572
>>> dont_measure fsmagic=0x64626720
>>> dont_measure fsmagic=0x1021994
>>> dont_measure fsmagic=0x858458f6
>>> dont_measure fsmagic=0x73636673
>>> measure func=BPRM_CHECK
>>> measure func=MMAP_CHECK mask=MAY_EXEC
>>> measure func=MODULE_CHECK uid=0
>>> measure func=LSM_STATE template=ima-buf
>>> measure func=LSM_POLICY
>>>
>>> Also, I noticed the following in my dmesg output:
>>> [   68.870715] ------------[ cut here ]------------
>>> [   68.870715] WARNING: CPU: 2 PID: 1 at mm/page_alloc.c:4826
>>> __alloc_pages_nodemask+0x627/0x700
>>> [   68.870715] Modules linked in: 8139too crct10dif_pclmul
>>> crc32_pclmul crc32c_intel ghash_clmulni_intel qxl serio_raw
>>> drm_ttm_helper ttm drm_kms_helper virtio_console cec drm 8139cp
>>> ata_generic mii pata_acpi floppy qemu_fw_cfg fuse
>>> [   68.870715] CPU: 2 PID: 1 Comm: systemd Not tainted 5.8.0-rc2+ #44
>>> [   68.870715] RIP: 0010:__alloc_pages_nodemask+0x627/0x700
>>> [   68.870715] Code: ff ff 75 6c 48 8b 85 48 ff ff ff 4c 89 c2 44 89
>>> e6 44 89 ff 41 c6 45 d0 00 49 89 45 b8 e8 41 e2 ff ff 49 89 c6 e9 9d
>>> fc ff ff <0f> 0b e9 d4 fd ff ff 0f 0b e9 bc fc ff ff 0f 0b e9 f9 fd ff
>>> ff e8
>>> [   68.870715] RSP: 0000:ffff8881e82a7a18 EFLAGS: 00010246
>>> [   68.870715] RAX: ffffed103d054f48 RBX: 1ffff1103d054f48 RCX: 
>>> 0000000000000000
>>> [   68.870715] RDX: 0000000000000000 RSI: 000000000000000b RDI: 
>>> 0000000000000000
>>> [   68.870715] RBP: ffff8881e82a7ae8 R08: ffffffffaa3fe2d5 R09: 
>>> 0000000000000001
>>> [   68.870715] R10: fffffbfff5a88f0f R11: 0000000000000001 R12: 
>>> 00000000007eef6a
>>> [   68.870715] R13: 0000000000040cc0 R14: 000000000000000b R15: 
>>> ffffffffadde766b
>>> [   68.870715] FS:  00007fdeb168c600(0000) GS:ffff8881e9800000(0000)
>>> knlGS:0000000000000000
>>> [   68.870715] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> [   68.870715] CR2: 00007fdeb17dd1d6 CR3: 00000001cc2d2002 CR4: 
>>> 00000000003606e0
>>> [   68.870715] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 
>>> 0000000000000000
>>> [   68.870715] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 
>>> 0000000000000400
>>> [   68.870715] Call Trace:
>>> [   68.870715]  ? sched_clock_cpu+0xf5/0x110
>>> [   68.870715]  ? __alloc_pages_slowpath.constprop.0+0x17a0/0x17a0
>>> [   68.870715]  ? match_held_lock+0x2e/0x240
>>> [   68.870715]  ? policy_nodemask+0x1a/0xa0
>>> [   68.870715]  ? policy_node+0x56/0x60
>>> [   68.870715]  kmalloc_order+0x25/0xc0
>>> [   68.870715]  kmalloc_order_trace+0x1d/0x140
>>> [   68.870715]  kmemdup+0x1a/0x40
>>> [   68.870715]  ima_queue_data+0x61/0x370
>>> [   68.870715]  ima_measure_lsm_data+0x32/0x60
>>> [   68.870715]  selinux_measure_state+0x2b8/0x2bd
>>> [   68.870715]  ? selinux_event_name+0xe0/0xe0
>>> [   68.870715]  ? rcu_is_watching+0x39/0x50
>>> [   68.870715]  security_load_policy+0x44c/0x8e0
>>> [   68.870715]  ? mark_lock+0xa6/0xbd0
>>> [   68.870715]  ? security_change_sid+0x90/0x90
>>> [   68.870715]  ? mark_held_locks+0x3e/0xa0
>>> [   68.870715]  ? lockdep_hardirqs_on_prepare+0x100/0x260
>>> [   68.870715]  ? asm_exc_page_fault+0x1e/0x30
>>> [   68.870715]  ? lockdep_hardirqs_on+0xc5/0x1b0
>>> [   68.870715]  ? asm_exc_page_fault+0x1e/0x30
>>> [   68.870715]  ? copy_user_enhanced_fast_string+0xe/0x30
>>> [   68.870715]  sel_write_load+0x157/0x260
>>> [   68.870715]  vfs_write+0x135/0x290
>>> [   68.870715]  ksys_write+0xb1/0x140
>>> [   68.870715]  ? __ia32_sys_read+0x50/0x50
>>> [   68.870715]  ? lockdep_hardirqs_on_prepare+0x100/0x260
>>> [   68.870715]  ? do_syscall_64+0x12/0xb0
>>> [   68.870715]  do_syscall_64+0x52/0xb0
>>> [   68.870715]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>> [   68.870715] RIP: 0033:0x7fdeb2539497
>>> [   68.870715] Code: Bad RIP value.
>>> [   68.870715] RSP: 002b:00007fff6352b308 EFLAGS: 00000246 ORIG_RAX:
>>> 0000000000000001
>>> [   68.870715] RAX: ffffffffffffffda RBX: 0000000000000020 RCX: 
>>> 00007fdeb2539497
>>> [   68.870715] RDX: 00000000007eef6a RSI: 00007fdeb0de1000 RDI: 
>>> 0000000000000004
>>> [   68.870715] RBP: 0000000000000004 R08: 00007fdeb25d0040 R09: 
>>> 00007fff6352b1a0
>>> [   68.870715] R10: 0000000000000000 R11: 0000000000000246 R12: 
>>> 00007fdeb0de1000
>>> [   68.870715] R13: 00000000007eef6a R14: 000000000000000f R15: 
>>> 0000000000000003
>>> [   68.870715] irq event stamp: 23486085
>>> [   68.870715] hardirqs last  enabled at (23486085):
>>> [<ffffffffaa419406>] _raw_spin_unlock_irqrestore+0x46/0x60
>>> [   68.870715] hardirqs last disabled at (23486084):
>>> [<ffffffffaa419443>] _raw_spin_lock_irqsave+0x23/0x90
>>> [   68.870715] softirqs last  enabled at (23486074):
>>> [<ffffffffaa8004f3>] __do_softirq+0x4f3/0x662
>>> [   68.870715] softirqs last disabled at (23486067):
>>> [<ffffffffaa601072>] asm_call_on_stack+0x12/0x20
>>> [   68.870715] ---[ end trace fb02740ff6f4d0cd ]---
>>
>> I think one issue here is that systemd loads SELinux policy first, 
>> then IMA policy, so it doesn't know whether it needs to measure 
>> SELinux policy on first policy load, and another issue is that the 
>> policy is too large to just queue the policy data itself this way (or 
>> you need to use an allocator that can handle larger sizes).
>>
>
> The problem seems to be that a lock is held when the IMA hook to 
> measure the LSM state is called. So memory allocation is not allowed, 
> but the hook is doing an allocation. I'll address this - thanks for 
> catching it.
>
> I have the following CONFIGs enabled, but I still don't see the above 
> issue on my machine.
>
The warning has to do with the memory allocation order being above the 
max order supported for kmalloc.  I think the problem is that 
ima_alloc_data_entry() is using kmemdup() to duplicate a payload of 
arbitrary size.  Policies on e.g. Fedora can be quite large, so you 
can't assume they can be allocated with kmalloc and friends.