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[84.106.84.65]) by smtp.gmail.com with ESMTPSA id i6sm21515015eda.79.2019.08.07.12.58.12 (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Wed, 07 Aug 2019 12:58:13 -0700 (PDT) Subject: Re: 5.3 boot regression caused by 5.3 TPM changes To: Ard Biesheuvel Cc: Matthew Garrett , Jarkko Sakkinen , Peter Huewe , Greg Kroah-Hartman , Thomas Gleixner , Ingo Molnar , linux-integrity , Linux Kernel Mailing List , linux-efi References: From: Hans de Goede Message-ID: <36a0d34b-bebe-009b-c67e-88005376b983@redhat.com> Date: Wed, 7 Aug 2019 21:58:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 05-08-19 18:01, Ard Biesheuvel wrote: > On Sun, 4 Aug 2019 at 19:12, Hans de Goede wrote: >> >> Hi, >> >> On 04-08-19 17:33, Ard Biesheuvel wrote: >>> Hi Hans, >>> >>> On Sun, 4 Aug 2019 at 13:00, Hans de Goede 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. 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