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

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Message-ID: <f992901f-6dca-7d31-3426-5a74d36c2c8c@gmail.com>
Date:   Mon, 3 Aug 2020 16:29:57 -0400
From:   Stephen Smalley <stephen.smalley.work@...il.com>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>, sashal@...nel.org,
        James Morris <jmorris@...ei.org>,
        linux-integrity@...r.kernel.org,
        SElinux list <selinux@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/4] LSM: Define SELinux function to measure state and
 policy

On 8/3/20 4:00 PM, Stephen Smalley wrote:

> On Mon, Aug 3, 2020 at 12:14 PM Lakshmi Ramasubramanian
> <nramas@...ux.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).