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

From: Dov Murik <dovmurik@linux.ibm.com>
To: Tom Lendacky <thomas.lendacky@amd.com>, linux-efi@vger.kernel.org
Cc: Laszlo Ersek <lersek@redhat.com>,
	Ashish Kalra <ashish.kalra@amd.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Andi Kleen <ak@linux.intel.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	James Bottomley <jejb@linux.ibm.com>,
	Tobin Feldman-Fitzthum <tobin@linux.ibm.com>,
	Jim Cadden <jcadden@ibm.com>,
	linux-coco@lists.linux.dev,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 2/3] efi: Reserve confidential computing secret area
Date: Tue, 29 Jun 2021 09:04:48 +0300	[thread overview]
Message-ID: <996db75c-5648-17b1-5bae-f3b10d72c110@linux.ibm.com> (raw)
In-Reply-To: <9b9b682f-297e-9ebd-4d67-43c3ed9ad8c5@amd.com>

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@linux.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
>>