linux-kernel - Re: [PATCH v5 2/7] tpm: remove definition of TPM2_ACTIVE_PCR

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Date:   Wed, 28 Nov 2018 13:17:22 +0100
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
CC:     <zohar@...ux.ibm.com>, <david.safford@...com>,
        <monty.wiseman@...com>, <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <silviu.vlasceanu@...wei.com>
Subject: Re: [PATCH v5 2/7] tpm: remove definition of TPM2_ACTIVE_PCR_BANKS

On 11/16/2018 2:38 PM, Jarkko Sakkinen wrote:
> On Wed, Nov 14, 2018 at 04:31:03PM +0100, Roberto Sassu wrote:
>> tcg_efi_specid_event and tcg_pcr_event2 declaration contains static arrays
>> for a list of hash algorithms used for event logs and event log digests.
>>
>> However, according to TCG EFI Protocol Specification, these arrays have
>> variable sizes. Setting the array size to zero or 3 does not make any
>> difference, because the parser has to adjust the offset depending on the
>> actual array size to access structure members after the static arrays.
>>
>> Thus, this patch removes the declaration of TPM2_ACTIVE_PCR_BANKS and sets
>> the array size to zero.
>>
>> Fixes: 4d23cc323cdb ("tpm: add securityfs support for TPM 2.0 firmware
>> event log")
>>
>> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
>> ---
>>   include/linux/tpm_eventlog.h | 5 ++---
>>   1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h
>> index 20d9da77fc11..3d5d162f09cc 100644
>> --- a/include/linux/tpm_eventlog.h
>> +++ b/include/linux/tpm_eventlog.h
>> @@ -8,7 +8,6 @@
>>   #define TCG_EVENT_NAME_LEN_MAX	255
>>   #define MAX_TEXT_EVENT		1000	/* Max event string length */
>>   #define ACPI_TCPA_SIG		"TCPA"	/* 0x41504354 /'TCPA' */
>> -#define TPM2_ACTIVE_PCR_BANKS	3
>>   
>>   #define EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2 0x1
>>   #define EFI_TCG2_EVENT_LOG_FORMAT_TCG_2   0x2
>> @@ -90,7 +89,7 @@ struct tcg_efi_specid_event {
>>   	u8 spec_errata;
>>   	u8 uintnsize;
>>   	u32 num_algs;
>> -	struct tcg_efi_specid_event_algs digest_sizes[TPM2_ACTIVE_PCR_BANKS];
>> +	struct tcg_efi_specid_event_algs digest_sizes[0];
>>   	u8 vendor_info_size;
>>   	u8 vendor_info[0];
>>   } __packed;
>> @@ -117,7 +116,7 @@ struct tcg_pcr_event2 {
>>   	u32 pcr_idx;
>>   	u32 event_type;
>>   	u32 count;
>> -	struct tpm2_digest digests[TPM2_ACTIVE_PCR_BANKS];
>> +	struct tpm2_digest digests[0];
>>   	struct tcg_event_field event;
>>   } __packed;
>>   
>> -- 
>> 2.17.1
>>
> 
> NAK for the same reason as last time.

I added this comment to include/linux/tpm_eventlog.h:

/*
  * http://www.trustedcomputinggroup.org/tcg-efi-protocol-specification/
  *
  * Set the size of 'digest_sizes' and 'digests', members of 
tcg_efi_specid_event
  * and tcg_pcr_event2, to zero. Structures with variable-sized arrays 
placed
  * midway are not suitable for type casting.
  */

Is it ok?

Thanks

Roberto


> /Jarkko
> 

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