linux-kernel - Re: [PATCH v2 5/5] virt: sevguest: Add TSM_REPORTS support for SNP_{GET, GET_EXT}

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Date:   Mon, 14 Aug 2023 09:22:59 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>,
        Dan Williams <dan.j.williams@...el.com>,
        <linux-coco@...ts.linux.dev>
CC:     Borislav Petkov <bp@...en8.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Dionna Glaze <dionnaglaze@...gle.com>,
        Brijesh Singh <brijesh.singh@....com>, <peterz@...radead.org>,
        <x86@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] virt: sevguest: Add TSM_REPORTS support for
 SNP_{GET, GET_EXT}_REPORT

Jeremi Piotrowski wrote:
> On 8/14/2023 9:43 AM, Dan Williams wrote:
> > The sevguest driver was a first mover in the confidential computing
> > space. As a first mover that afforded some leeway to build the driver
> > without concern for common infrastructure.
> > 
> > Now that sevguest is no longer a singleton [1] the common operation of
> > building and transmitting attestation report blobs can / should be made
> > common. In this model the so called "TSM-provider" implementations can
> > share a common envelope ABI even if the contents of that envelope remain
> > vendor-specific. When / if the industry agrees on an attestation record
> > format, that definition can also fit in the same ABI. In the meantime
> > the kernel's maintenance burden is reduced and collaboration on the
> > commons is increased.
> > 
> > Convert sevguest to use CONFIG_TSM_REPORTS to retrieve the blobs that
> > the SNP_{GET,GET_EXT}_REPORT ioctls produce. An example flow for
> > retrieving the SNP_GET_REPORT blob via the TSM interface utility,
> > assuming no nonce and VMPL==2:
> > 
> >     echo 2 > /sys/class/tsm/tsm0/privlevel
> >     dd if=/dev/urandom bs=64 count=1 | xxd -p -c 0 > /sys/class/tsm/tsm0/inhex
> >     hexdump -C /sys/class/tsm/tsm0/outblob
> > 
> > ...while the SNP_GET_EXT_REPORT flow needs to additionally set the
> > format to "extended":
> > 
> >     echo 2 > /sys/class/tsm/tsm0/privlevel
> >     echo extended > /sys/class/tsm/tsm0/format
> >     dd if=/dev/urandom bs=64 count=1 | xxd -p -c 0 > /sys/class/tsm/tsm0/inhex
> >     hexdump -C /sys/class/tsm/tsm0/outblob
> > 
> > The old ioctls can be lazily deprecated, the main motivation of this
> > effort is to stop the proliferation of new ioctls, and to increase
> > cross-vendor colloboration.
> > 
> > Note, only compile-tested.
> > 
> > Link: http://lore.kernel.org/r/64961c3baf8ce_142af829436@dwillia2-xfh.jf.intel.com.notmuch [1]
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Tom Lendacky <thomas.lendacky@....com>
> > Cc: Dionna Glaze <dionnaglaze@...gle.com>
> > Cc: Brijesh Singh <brijesh.singh@....com>
> > Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> > ---
> >  drivers/virt/coco/sev-guest/Kconfig     |    1 
> >  drivers/virt/coco/sev-guest/sev-guest.c |   81 +++++++++++++++++++++++++++++++
> >  2 files changed, 82 insertions(+)
> > 
> > diff --git a/drivers/virt/coco/sev-guest/Kconfig b/drivers/virt/coco/sev-guest/Kconfig
> > index da2d7ca531f0..1cffc72c41cb 100644
> > --- a/drivers/virt/coco/sev-guest/Kconfig
> > +++ b/drivers/virt/coco/sev-guest/Kconfig
> > @@ -5,6 +5,7 @@ config SEV_GUEST
> >  	select CRYPTO
> >  	select CRYPTO_AEAD2
> >  	select CRYPTO_GCM
> > +	select TSM_REPORTS
> >  	help
> >  	  SEV-SNP firmware provides the guest a mechanism to communicate with
> >  	  the PSP without risk from a malicious hypervisor who wishes to read,
> > diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> > index f48c4764a7a2..5941081502e8 100644
> > --- a/drivers/virt/coco/sev-guest/sev-guest.c
> > +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> > @@ -16,6 +16,7 @@
> >  #include <linux/miscdevice.h>
> >  #include <linux/set_memory.h>
> >  #include <linux/fs.h>
> > +#include <linux/tsm.h>
> >  #include <crypto/aead.h>
> >  #include <linux/scatterlist.h>
> >  #include <linux/psp-sev.h>
> > @@ -769,6 +770,78 @@ static u8 *get_vmpck(int id, struct snp_secrets_page_layout *layout, u32 **seqno
> >  	return key;
> >  }
> >  
> > +static u8 *sev_report_new(struct device *dev, const struct tsm_desc *desc,
> > +			  size_t *outblob_len)
> 
> get_report and get_ext_report both have a:
> 
>     lockdep_assert_held(&snp_cmd_mutex);
> 
> so you'd need to take that lock somewhere here.

Got it, and in general this needs testing from someone with actual
hardware.