linux-kernel - Re: [PATCH v4 2/6] tpm: remove definition of TPM2_ACTIVE_PCR

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Date:   Thu, 8 Nov 2018 15:52:28 +0100
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
CC:     <zohar@...ux.ibm.com>, <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <silviu.vlasceanu@...wei.com>
Subject: Re: [PATCH v4 2/6] tpm: remove definition of TPM2_ACTIVE_PCR_BANKS

On 11/8/2018 3:03 PM, Jarkko Sakkinen wrote:
> On Thu, Nov 08, 2018 at 04:02:08PM +0200, Jarkko Sakkinen wrote:
>> On Tue, Nov 06, 2018 at 04:01:55PM +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 and are not suitable for parsing events with type casting.
>>>
>>> Since declaring static arrays with hard-coded sizes does not help to parse
>>> data after these arrays, this patch removes the declaration of
>>> TPM2_ACTIVE_PCR_BANKS and sets the size of the arrays above 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;
>>
>> Last two fields make sense at least without comment as they overlap.
> 
> i.e. would be semantically equal to
> 
> union {
> 	struct tpm2_digest digests[0];
> 	struct tcg_event_field event;
> };

I didn't understand. Should I add the union?

Roberto


> /Jarkko
> 

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