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Message-ID: <64da54e35d473_2138e2945f@dwillia2-xfh.jf.intel.com.notmuch>
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.
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