Re: [Regression] "tpm: Require that all digests are present in TCG_PCR_EVENT2 structures" causes null pointer dereference

[Kai-Heng Feng]

> On Oct 21, 2020, at 13:48, Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx> wrote:
> 
> On 2020-10-20 17:07:50, Mimi Zohar wrote:
>> On Tue, 2020-09-29 at 13:52 -0400, Mimi Zohar wrote:
>>> On Mon, 2020-09-28 at 22:16 +0800, Kai-Heng Feng wrote:
>>>> Hi Jarkko,
>>>> 
>>>>> On Sep 28, 2020, at 22:06, Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote:
>>>>> 
>>>>> On Mon, Sep 28, 2020 at 08:31:04PM +0800, Kai-Heng Feng wrote:
>>>>>> Commit 7f3d176f5f7e "tpm: Require that all digests are present in
>>>>>> TCG_PCR_EVENT2 structures" causes a null pointer dereference on all
>>>>>> laptops I have:
>>>>> 
>>>>> ...
>>>>> 
>>>>>> [   17.868849] BUG: kernel NULL pointer dereference, address: 000000000000002c
>>>>>> [   17.868852] #PF: supervisor read access in kernel mode
>>>>>> [   17.868854] #PF: error_code(0x0000) - not-present page
>>>>>> [   17.868855] PGD 0 P4D 0 
>>>>>> [   17.868858] Oops: 0000 [#1] SMP PTI
>>>>>> [   17.868860] CPU: 0 PID: 1873 Comm: fwupd Not tainted 5.8.0-rc6+ #25
>>>>>> [   17.868861] Hardware name: LENOVO 20LAZ3TXCN/20LAZ3TXCN, BIOS N27ET38W (1.24 ) 11/28/2019
>>>>>> [   17.868866] RIP: 0010:tpm2_bios_measurements_start+0x38/0x1f0
>>>>>> [   17.868868] Code: 55 41 54 53 48 83 ec 30 4c 8b 16 65 48 8b 04 25 28 00 00 00 48 89 45 d0 48 8b 47 70 4c 8b a0 d0 06 00 00 48 8b 88 d8 06 00 00 <41> 8b 5c 24 1c 48 89 4d b0 48 89 d8 48 83 c3 20 4d 85 d2 75 31 4c
>>>>>> [   17.868869] RSP: 0018:ffff9da500a9fde0 EFLAGS: 00010282
>>>>>> [   17.868871] RAX: ffff917d03dc4000 RBX: 0000000000000000 RCX: 0000000000000010
>>>>>> [   17.868872] RDX: 0000000000001000 RSI: ffff917c99b19460 RDI: ffff917c99b19438
>>>>>> [   17.868873] RBP: ffff9da500a9fe38 R08: ffffbda4ffa33fc0 R09: ffff917cbfeae4c0
>>>>>> [   17.868874] R10: 0000000000000000 R11: 0000000000000002 R12: 0000000000000010
>>>>>> [   17.868875] R13: ffff917c99b19438 R14: ffff917c99b19460 R15: ffff917c99b19470
>>>>>> [   17.868876] FS:  00007f9d80988b00(0000) GS:ffff917d07400000(0000) knlGS:0000000000000000
>>>>>> [   17.868877] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>>> [   17.868878] CR2: 000000000000002c CR3: 0000000219b12004 CR4: 00000000003606f0
>>>>>> [   17.868879] Call Trace:
>>>>>> [   17.868884]  seq_read+0x95/0x470
>>>>>> [   17.868887]  ? security_file_permission+0x150/0x160
>>>>>> [   17.868889]  vfs_read+0xaa/0x190
>>>>>> [   17.868891]  ksys_read+0x67/0xe0
>>>>>> [   17.868893]  __x64_sys_read+0x1a/0x20
>>>>>> [   17.868896]  do_syscall_64+0x52/0xc0
>>>>>> [   17.868898]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>>>> [   17.868900] RIP: 0033:0x7f9d83be91dc
>>>>>> [   17.868901] Code: Bad RIP value.
>>>>>> [   17.868902] RSP: 002b:00007fff7f5e0250 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
>>>>>> [   17.868903] RAX: ffffffffffffffda RBX: 00005651d262f420 RCX: 00007f9d83be91dc
>>>>>> [   17.868904] RDX: 0000000000001000 RSI: 00007fff7f5e0350 RDI: 0000000000000010
>>>>>> [   17.868905] RBP: 00007f9d83cc54a0 R08: 0000000000000000 R09: 00005651d26c1830
>>>>>> [   17.868906] R10: 00005651d2582010 R11: 0000000000000246 R12: 0000000000001000
>>>>>> [   17.868907] R13: 00007fff7f5e0350 R14: 0000000000000d68 R15: 00007f9d83cc48a0
>>>>>> [   17.868909] Modules linked in: rfcomm ccm cmac algif_hash algif_skcipher af_alg snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic bnep joydev mei_hdcp wmi_bmof intel_rapl_msr intel_wmi_thunderbolt x86_pkg_temp_thermal intel_powerclamp coretemp nls_iso8859_1 kvm_intel kvm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel glue_helper crypto_simd cryptd rapl input_leds intel_cstate snd_hda_intel snd_intel_dspcfg rmi_smbus iwlmvm snd_hda_codec serio_raw snd_hwdep mac80211 rmi_core snd_hda_core libarc4 uvcvideo snd_pcm videobuf2_vmalloc btusb videobuf2_memops iwlwifi videobuf2_v4l2 btrtl btbcm videobuf2_common btintel thunderbolt i915 bluetooth mei_me videodev thinkpad_acpi nvram cfg80211 ledtrig_audio mei mc ecdh_generic ecc i2c_algo_bit processor_thermal_device snd_seq_midi drm_kms_helper snd_seq_midi_event intel_soc_dts_iosf syscopyarea sysfillrect snd_rawmidi intel_pch_thermal sysimgblt intel_rapl_common intel_xhci_usb_role_switch fb_sys_fops
>>  u
>>> cs
>>>> i_acpi r
>>>> o
>>>>> les cec
>>>>>> [   17.868935]  typec_ucsi typec nxp_nci_i2c snd_seq nxp_nci wmi nci nfc snd_timer snd_seq_device snd int3403_thermal soundcore int340x_thermal_zone video mac_hid int3400_thermal acpi_pad acpi_thermal_rel sch_fq_codel parport_pc ppdev lp parport drm ip_tables x_tables autofs4 btrfs blake2b_generic libcrc32c xor zstd_compress raid6_pq uas usb_storage psmouse e1000e nvme i2c_i801 i2c_smbus nvme_core intel_lpss_pci intel_lpss idma64 virt_dma pinctrl_sunrisepoint pinctrl_intel
>>>>>> [   17.868951] CR2: 000000000000002c
>>>>>> [   17.868953] ---[ end trace ee7716fff5dec2fb ]---
>>>>>> [   17.868955] RIP: 0010:tpm2_bios_measurements_start+0x38/0x1f0
>>>>>> [   17.868957] Code: 55 41 54 53 48 83 ec 30 4c 8b 16 65 48 8b 04 25 28 00 00 00 48 89 45 d0 48 8b 47 70 4c 8b a0 d0 06 00 00 48 8b 88 d8 06 00 00 <41> 8b 5c 24 1c 48 89 4d b0 48 89 d8 48 83 c3 20 4d 85 d2 75 31 4c
>>>>>> [   17.868958] RSP: 0018:ffff9da500a9fde0 EFLAGS: 00010282
>>>>>> [   17.868959] RAX: ffff917d03dc4000 RBX: 0000000000000000 RCX: 0000000000000010
>>>>>> [   17.868960] RDX: 0000000000001000 RSI: ffff917c99b19460 RDI: ffff917c99b19438
>>>>>> [   17.868961] RBP: ffff9da500a9fe38 R08: ffffbda4ffa33fc0 R09: ffff917cbfeae4c0
>>>>>> [   17.868962] R10: 0000000000000000 R11: 0000000000000002 R12: 0000000000000010
>>>>>> [   17.868963] R13: ffff917c99b19438 R14: ffff917c99b19460 R15: ffff917c99b19470
>>>>>> [   17.868964] FS:  00007f9d80988b00(0000) GS:ffff917d07400000(0000) knlGS:0000000000000000
>>>>>> [   17.868965] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>>> [   17.868966] CR2: 000000000000002c CR3: 0000000219b12004 CR4: 00000000003606f0
>>>>> 
>>>>> It is possible but initially feels a bit weird:
>>>>> 
>>>>> -                  sizeof(TCG_SPECID_SIG)) || count > efispecid->num_algs) {
>>>>> +                  sizeof(TCG_SPECID_SIG)) ||
>>>>> +           !efispecid->num_algs || count != efispecid->num_algs) {
>>>>> 
>>>>> Assuming that check does not pass because of a more strict constraint,
>>>>> __calc_tpm2_event_size() returns 0.
>>>>> 
>>>>> It is wrapped like this in drivers/char/tpm/eventlog/tpm2.c:
>>>>> 
>>>>> static size_t calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
>>>>> 				   struct tcg_pcr_event *event_header)
>>>>> {
>>>>> 	return __calc_tpm2_event_size(event, event_header, false);
>>>>> }
>>>>> 
>>>>> I.e. TPM_MEMUNMAP will not get executed because "do_mapping == false".
>>>>> tpm2_bios_measurements_start() checks for "size == 0" and returns NULL
>>>>> whenever this happens.
>>>>> 
>>>>> Are you 100% sure that it is exactly this commit that triggers the bug?
>>>> 
>>>> Yes I am 100% sure. The issue happens all the time, and never happens
>>>> if I checkout the previous commit.
>>> 
>>> I'm seeing this too on my test Ubuntu laptop.  Reverting the patch
>>> fixes it, but there's no data.
>> 
>> For a while I wasn't able to boot the test system with secure boot
>> enabled.  The NULL pointer dereference problem occurred during the
>> period of time that secure boot was disabled.   Once the secure boot
>> issue was resolved, the NULL pointer dereference problem was resolved
>> as well, when booting with/without secure boot enabled.
> 
> I noticed that Kai had disabled secure boot, as well. I found a Thinkpad
> with the same BIOS revision as Kai's Thinkpad (N27ET38W - 1.24) and
> tested an unpatched v5.9 kernel running on an up-to-date Ubuntu 20.04.1
> userspace. The main difference is that he has a Thinkpad T580 and I was
> using a Thinkpad P52s. I was unable to reproduce the crash either by
> running fwupdtpmevlog or cat'ing /sys/kernel/security/tpm0/binary_bios_measurements.
> 
> I noticed that Kai had cleared his secure boot allowed signature
> database (db) so I also tried that but was still unsuccessful in
> reproducing the crash.
> 
> Of course, I also tested with secure boot enabled and also after
> toggling every secure boot and TPM related option in the BIOS. Still no
> luck.
> 
> Kenneth mentioned elsewhere[1] that he experienced the crash with
> Ubuntu's 5.8.0-18 kernel so I also tried that but still no luck.
> 
> Everyone that has reported this crash[1][2][3][4] seems to have been
> running with an Ubuntu userspace. I do see that Ubuntu recently fixed a
> shim bug[5] on Sept 24. Ubuntu auto-installs security updates by default
> but this was not a security update so perhaps folks that were initially
> affected by this crash hadn't yet applied the update. It looks unrelated
> to me but it might explain why I can't reproduce this crash now, how the
> crash no longer affects Mimi, and why nobody else is complaining about
> the crash in recent weeks.
> 
> Kai, could you please try once more with v5.9 and ensuring that your
> Ubuntu system is fully updated?

Yes it's fully updated.

> If you're able to reproduce it with
> v5.9, please send me your kernel config and your raw

Ok, please refer to attachment.

> /sys/kernel/security/tpm0/binary_bios_measurements file contents after
> rebooting into a working kernel. I really appreciate it!

Hmm, it's empty.

Kai-Heng

Attachment: config-5.10.0-rc1
Description: Binary data

Attachment: dmesg
Description: Binary data

> 
> Tyler
> 
> [1] https://lore.kernel.org/linux-integrity/alpine.DEB.2.23.453.2009121522400.7398@xps-7390/
> [2] https://lore.kernel.org/lkml/E1FDCCCB-CA51-4AEE-AC83-9CDE995EAE52@xxxxxxxxxxxxx/
> [3] https://lore.kernel.org/lkml/846fe4da67d05f57fba33e38c9a6e394e657adc3.camel@xxxxxxxxxxxxx/
> [4] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1898998
> [5] https://bugs.launchpad.net/ubuntu/+source/shim/+bug/1864223
> 
>> 
>> Mimi