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[84.106.84.65]) by smtp.gmail.com with ESMTPSA id 17sm21513114edu.21.2019.08.07.13.13.41 (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Wed, 07 Aug 2019 13:13:41 -0700 (PDT) Subject: Re: 5.3 boot regression caused by 5.3 TPM changes From: Hans de Goede 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: <36a0d34b-bebe-009b-c67e-88005376b983@redhat.com> Message-ID: Date: Wed, 7 Aug 2019 22:13:40 +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: <36a0d34b-bebe-009b-c67e-88005376b983@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org 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 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. 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