linux-kernel - Re: [RFC PATCH v2 2/3] efi: Reserve confidential computing secret area

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Message-ID: <996db75c-5648-17b1-5bae-f3b10d72c110@linux.ibm.com>
Date:   Tue, 29 Jun 2021 09:04:48 +0300
From:   Dov Murik <dovmurik@...ux.ibm.com>
To:     Tom Lendacky <thomas.lendacky@....com>, linux-efi@...r.kernel.org
Cc:     Laszlo Ersek <lersek@...hat.com>,
        Ashish Kalra <ashish.kalra@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@...ux.ibm.com>,
        Jim Cadden <jcadden@....com>, linux-coco@...ts.linux.dev,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 2/3] efi: Reserve confidential computing secret
 area

Hi Tom,

On 28/06/2021 23:40, Tom Lendacky wrote:
> On 6/28/21 1:34 PM, Dov Murik wrote:
>> When efi-stub copies an EFI-provided confidential computing secret area,
>> reserve that memory block for future use within the kernel.
>>
>> Signed-off-by: Dov Murik <dovmurik@...ux.ibm.com>
>> ---
>>  drivers/firmware/efi/Makefile                 |  2 +-
>>  drivers/firmware/efi/confidential-computing.c | 41 +++++++++++++++++++
>>  drivers/firmware/efi/efi.c                    |  5 +++
>>  include/linux/efi.h                           |  4 ++
>>  4 files changed, 51 insertions(+), 1 deletion(-)
>>  create mode 100644 drivers/firmware/efi/confidential-computing.c
>>
>> diff --git a/include/linux/efi.h b/include/linux/efi.h
>> index 4f647f1ee298..e9740bd16db0 100644
>> --- a/include/linux/efi.h
>> +++ b/include/linux/efi.h
>> @@ -551,6 +551,8 @@ extern struct efi {
>>  	unsigned long			tpm_log;		/* TPM2 Event Log table */
>>  	unsigned long			tpm_final_log;		/* TPM2 Final Events Log table */
>>  	unsigned long			mokvar_table;		/* MOK variable config table */
>> +	unsigned long			confidential_computing_secret;	/* Confidential computing */
>> +									/* secret table           */
> 
> If there is any possibility that someone could reuse a form of this
> confidential computing secret table in a bare metal system, then this
> table needs to be added to the efi_tables[] array in
> arch/x86/platform/efi/efi.c. Otherwise, it will be mapped improperly on a
> system with SME active.

Good catch, thanks.  I see that all existing table addresses from
struct efi are added to the efi_tables[] array, so for completeness it
makes sense to add efi.confidential_computing_secret as well (even
though currently bare metal firmware doesn't have this table).

Thanks,
-Dov


> 
> Thanks,
> Tom
> 
>>  
>>  	efi_get_time_t			*get_time;
>>  	efi_set_time_t			*set_time;
>> @@ -1190,6 +1192,8 @@ extern int efi_tpm_final_log_size;
>>  
>>  extern unsigned long rci2_table_phys;
>>  
>> +extern int efi_confidential_computing_secret_area_reserve(void);
>> +
>>  /*
>>   * efi_runtime_service() function identifiers.
>>   * "NONE" is used by efi_recover_from_page_fault() to check if the page
>>