linux-kernel - Re: [RFC PATCH v2 3/3] virt: Add sev_secret module to expose confidential computing secrets

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Message-ID: <6e35f6db-9c5b-3c75-a66b-de1392295f6a@linux.ibm.com>
Date:   Tue, 29 Jun 2021 10:23:49 +0300
From:   Dov Murik <dovmurik@...ux.ibm.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     linux-efi@...r.kernel.org, Laszlo Ersek <lersek@...hat.com>,
        Ashish Kalra <ashish.kalra@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....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, Dov Murik <dovmurik@...ux.ibm.com>
Subject: Re: [RFC PATCH v2 3/3] virt: Add sev_secret module to expose
 confidential computing secrets



On 28/06/2021 22:30, Borislav Petkov wrote:
> On Mon, Jun 28, 2021 at 06:34:31PM +0000, Dov Murik wrote:
>> The new sev_secret module exposes the confidential computing secret area
>> via securityfs interface.
>>
>> When the module is loaded (and securityfs is mounted, typically under
>> /sys/kernel/security), an "sev_secret" directory is created in
>> securityfs.  In it, a file is created for each secret entry.  The name
>> of each such file is the GUID of the secret entry, and its content is
>> the secret data.
>>
>> This allows applications running in a confidential computing setting to
>> read secrets provided by the guest owner via a secure secret injection
>> mechanism (such as AMD SEV's LAUNCH_SECRET command).
>>
>> Removing (unlinking) files in the "sev_secret" directory will zero out
>> the secret in memory, and remove the filesystem entry.  If the module
>> is removed and loaded again, that secret will not appear in the
>> filesystem.
>>
>> Signed-off-by: Dov Murik <dovmurik@...ux.ibm.com>
>> ---
>>  drivers/virt/Kconfig                 |   2 +
>>  drivers/virt/Makefile                |   1 +
>>  drivers/virt/sev_secret/Kconfig      |  11 +
>>  drivers/virt/sev_secret/Makefile     |   2 +
>>  drivers/virt/sev_secret/sev_secret.c | 298 +++++++++++++++++++++++++++
>>  5 files changed, 314 insertions(+)
>>  create mode 100644 drivers/virt/sev_secret/Kconfig
>>  create mode 100644 drivers/virt/sev_secret/Makefile
>>  create mode 100644 drivers/virt/sev_secret/sev_secret.c
> 
> Same question here: maybe have 
> 
> drivers/virt/coco/
> 
> and put all coco guest stuff in there.
> 

I agree, according to what comes up of the conversation we have in
replies to the cover letter.


>> diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
>> index 8061e8ef449f..c222cc625891 100644
>> --- a/drivers/virt/Kconfig
>> +++ b/drivers/virt/Kconfig
>> @@ -36,4 +36,6 @@ source "drivers/virt/vboxguest/Kconfig"
>>  source "drivers/virt/nitro_enclaves/Kconfig"
>>  
>>  source "drivers/virt/acrn/Kconfig"
>> +
>> +source "drivers/virt/sev_secret/Kconfig"
>>  endif
>> diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
>> index 3e272ea60cd9..0765e5418d1d 100644
>> --- a/drivers/virt/Makefile
>> +++ b/drivers/virt/Makefile
>> @@ -8,3 +8,4 @@ obj-y				+= vboxguest/
>>  
>>  obj-$(CONFIG_NITRO_ENCLAVES)	+= nitro_enclaves/
>>  obj-$(CONFIG_ACRN_HSM)		+= acrn/
>> +obj-y				+= sev_secret/
>> diff --git a/drivers/virt/sev_secret/Kconfig b/drivers/virt/sev_secret/Kconfig
>> new file mode 100644
>> index 000000000000..4505526b8ef1
>> --- /dev/null
>> +++ b/drivers/virt/sev_secret/Kconfig
>> @@ -0,0 +1,11 @@
>> +# SPDX-License-Identifier: GPL-2.0-only
>> +config AMD_SEV_SECRET_SECURITYFS
>> +	tristate "AMD SEV secret area securityfs support"
>> +	depends on EFI
> 
> That probably needs to depend on CONFIG_AMD_MEM_ENCRYPT - otherwise
> what's the point for it.
> 

But not if it's a generic driver that is useful for other confidential
computing implementations.  Consider some non-encrypting guest memory
isolation mechanism where the host can't read most guest pages; this
module might be useful there too.

Also, isn't it a bit weird to depend on CONFIG_AMD_MEM_ENCRYPT but not
use any of its APIs?


-Dov