Re: 5.3 boot regression caused by 5.3 TPM changes

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 07-08-19 21:58, Hans de Goede wrote:
> Hi,
> 
> On 05-08-19 18:01, Ard Biesheuvel wrote:
>> On Sun, 4 Aug 2019 at 19:12, Hans de Goede <hdegoede@redhat.com> wrote:
>>>
>>> Hi,
>>>
>>> On 04-08-19 17:33, Ard Biesheuvel wrote:
>>>> Hi Hans,
>>>>
>>>> On Sun, 4 Aug 2019 at 13:00, Hans de Goede <hdegoede@redhat.com> wrote:
>>>>>
>>>>> Hi All,
>>>>>
>>>>> While testing 5.3-rc2 on an Irbis TW90 Intel Cherry Trail based
>>>>> tablet I noticed that it does not boot on this device.
>>>>>
>>>>> A git bisect points to commit 166a2809d65b ("tpm: Don't duplicate
>>>>> events from the final event log in the TCG2 log")
>>>>>
>>>>> And I can confirm that reverting just that single commit makes
>>>>> the TW90 boot again.
>>>>>
>>>>> This machine uses AptIO firmware with base component versions
>>>>> of: UEFI 2.4 PI 1.3. I've tried to reproduce the problem on
>>>>> a Teclast X80 Pro which is also CHT based and also uses AptIO
>>>>> firmware with the same base components. But it does not reproduce
>>>>> there. Neither does the problem reproduce on a CHT tablet using
>>>>> InsideH20 based firmware.
>>>>>
>>>>> Note that these devices have a software/firmware TPM-2.0
>>>>> implementation, they do not have an actual TPM chip.
>>>>>
>>>>> Comparing TPM firmware setting between the 2 AptIO based
>>>>> tablets the settings are identical, but the troublesome
>>>>> TW90 does have some more setting then the X80, it has
>>>>> the following settings which are not shown on the X80:
>>>>>
>>>>> Active PCR banks:           SHA-1         (read only)
>>>>> Available PCR banks:        SHA-1,SHA256  (read only)
>>>>> TPM2.0 UEFI SPEC version:   TCG_2         (other possible setting: TCG_1_2
>>>>> Physical Presence SPEC ver: 1.2           (other possible setting: 1.3)
>>>>>
>>>>> I have the feeling that at least the first 2 indicate that
>>>>> the previous win10 installation has actually used the
>>>>> TPM, where as on the X80 the TPM is uninitialized.
>>>>> Note this is just a hunch I could be completely wrong.
>>>>>
>>>>> I would be happy to run any commands to try and debug this
>>>>> or to build a kernel with some patches to gather more info.
>>>>>
>>>>> Note any kernel patches to printk some debug stuff need
>>>>> to be based on 5.3 with 166a2809d65b reverted, without that
>>>>> reverted the device will not boot, and thus I cannot collect
>>>>> logs without it reverted.
>>>>>
>>>>
>>>> Are you booting a 64-bit kernel on 32-bit firmware?
>>>
>>> Yes you are right, I must say that this is somewhat surprising
>>> most Cherry Trail devices do use 64 bit firmware (where as Bay Trail
>>> typically uses 32 bit). But I just checked efibootmgr output and it
>>> says it is booting: \EFI\FEDORA\SHIMIA32.EFI so yeah 32 bit firmware.
>>>
>>> Recent Fedora releases take care of this so seamlessly I did not
>>> even realize...
>>>
>>
>> OK, so we'll have to find out how this patch affects 64-bit code
>> running on 32-bit firmware.
> 
> I was not sure this really is a 32 bit firmware issue, as I believed
> I saw 5.3 running fine on other 32 bit firmware devices, so I tried
> this on another device with 32 bit UEFI and you're right this is a
> 32 bit issue.
> 
>> The only EFI call in that patch is
>> get_config_table(), which is not actually a EFI boot service call but
>> a EFI stub helper that parses the config table array in the EFI system
>> table.
> 
> Well get_efi_config_table() is a new function in 5.3, introduced
> specifically for the 166a2809d65b ("tpm: Don't duplicate events from the
> final event log in the TCG2 log") commit.
> 
> It was introduced in commit 82d736ac56d7 ("Abstract out support for
> locating an EFI config table") and after taking a good look at this
> commit I'm pretty confident to say that the new get_efi_config_table()
> function is the problem, as it is broken in multiple ways.
> 
> In itself the new get_efi_config_table() is just factoring out some
> code used in drivers/firmware/efi/libstub/fdt.c into a new helper
> for reuse and not making any functional changes to the factored out
> code.
> 
> The problem is that the old code which it factors out contains a number
> of assumptions which are true in the get_fdt() context from which it
> was called but are not true when used in more generic code as is done
> from the 166a2809d65b ("tpm: Don't duplicate events from the
> final event log in the TCG2 log") commit.
> 
> There are 2 problems with the new get_efi_config_table() function:
> 
> 1) sys_table->tables contains a physical address, we cannot just
> cast that to a pointer and deref it, it needs to be early_memremap-ed
> and then we deref the mapping. I'm somewhat amazed that this works
> at all for the 64 bit case, but apparently it does.
> 
> 2) sys_table->tables points to either an array of either
> efi_config_table_64_t structd or an array of efi_config_table_32_t
> structs.  efi_config_table_t is a generic type for storing information
> when parsing it should NOT be used for reading the actual tables
> as they come from the firmware when parsing! Now efi_config_table_t
> happens to be an exact match for efi_config_table_64_t when building
> an x86_64 kernel, so this happens to work for the 64 bit firmware case.
> 
> The properway to deal with this would be to use the existing
> efi_config_parse_tables() functionality from drivers/firmware/efi/efi.c
> by adding entry for the LINUX_EFI_TPM_FINAL_LOG_GUID to the
> common_tables[] array in drivers/firmware/efi/efi.c and make that
> entry store the table address (if found) in a new efi.final_log
> member.

There actually already is a efi.tpm_final_log member where the
table's physical address is waiting for us all pre-parsed and ready
to use ...

> I'm not sure how important this functionality is to have in 5.3.
> 
> I will try to come up with a fix for this using efi_config_parse_tables()
> but it might be better to just revert for 5.3 .

Regards,

Hans