Re: [PATCH] efistub/tpm: Use ACPI reclaim memory for event log to avoid corruption

[Jiri Slaby <jirislaby@kernel.org>]

On 24. 10. 24, 18:20, Jiri Slaby wrote:
> On 12. 09. 24, 17:52, Ard Biesheuvel wrote:
>> From: Ard Biesheuvel <ardb@kernel.org>
>>
>> The TPM event log table is a Linux specific construct, where the data
>> produced by the GetEventLog() boot service is cached in memory, and
>> passed on to the OS using a EFI configuration table.
>>
>> The use of EFI_LOADER_DATA here results in the region being left
>> unreserved in the E820 memory map constructed by the EFI stub, and this
>> is the memory description that is passed on to the incoming kernel by
>> kexec, which is therefore unaware that the region should be reserved.
>>
>> Even though the utility of the TPM2 event log after a kexec is
>> questionable, any corruption might send the parsing code off into the
>> weeds and crash the kernel. So let's use EFI_ACPI_RECLAIM_MEMORY
>> instead, which is always treated as reserved by the E820 conversion
>> logic.
>>
>> Cc: <stable@vger.kernel.org>
>> Reported-by: Breno Leitao <leitao@debian.org>
>> Tested-by: Usama Arif <usamaarif642@gmail.com>
>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>> ---
>>   drivers/firmware/efi/libstub/tpm.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/firmware/efi/libstub/tpm.c b/drivers/firmware/ 
>> efi/libstub/tpm.c
>> index df3182f2e63a..1fd6823248ab 100644
>> --- a/drivers/firmware/efi/libstub/tpm.c
>> +++ b/drivers/firmware/efi/libstub/tpm.c
>> @@ -96,7 +96,7 @@ static void efi_retrieve_tcg2_eventlog(int version, 
>> efi_physical_addr_t log_loca
>>       }
>>       /* Allocate space for the logs and copy them. */
>> -    status = efi_bs_call(allocate_pool, EFI_LOADER_DATA,
>> +    status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
>>                    sizeof(*log_tbl) + log_size, (void **)&log_tbl);
> 
> Hi,
> 
> this, for some reason, corrupts system configuration table. On good 
> boots, memattr points to 0x77535018, on bad boots (this commit applied), 
> it points to 0x77526018.
> 
> And the good content at 0x77526018:
> tab=0x77526018 size=16+45*48=0x0000000000000880
> 
> bad content at 0x77535018:
> tab=0x77535018 size=16+2*1705353216=0x00000000cb4b4010
> 
> This happens only on cold boots. Subsequent boots (having the commit or 
> not) are all fine.
> 
> Any ideas?

====
EFI_ACPI_RECLAIM_MEMORY

This memory is to be preserved by the UEFI OS loader and OS until ACPI
is enabled. Once ACPI is enabled, the memory in this range is available 
for general use.
====

BTW doesn't the above mean it is released by the time TPM actually reads it?

Isn't the proper fix to actually memblock_reserve() that TPM portion. 
The same as memattr in efi_memattr_init()?

> DMI: Dell Inc. Latitude 7290/09386V, BIOS 1.39.0 07/04/2024
> 
> This was reported downstream at:
> https://bugzilla.suse.com/show_bug.cgi?id=1231465
> 
> thanks,
-- 
js
suse labs