Re: [PATCH v2 5/5] virt: sevguest: Add TSM_REPORTS support for SNP_{GET, GET_EXT}_REPORT
From: Tom Lendacky
Date: Tue Aug 15 2023 - 16:51:54 EST
On 8/14/23 02:43, 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.
I just got back from vacation, so I'll apply and test as soon as I get a
chance.
Link: http://lore.kernel.org/r/64961c3baf8ce_142af829436@xxxxxxxxxxxxxxxxxxxxxxxxx.notmuch [1]
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Dionna Glaze <dionnaglaze@xxxxxxxxxx>
Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
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)
+{
+ struct snp_guest_dev *snp_dev = dev_get_drvdata(dev);
+ const int report_size = SZ_16K;
The response buffer from the PSP is limited to 4K, so the report size can
be SZ_4K.
+ const int ext_size = SZ_16K;
+ int ret, size;
+
+ if (desc->inblob_len != 64)
+ return ERR_PTR(-EINVAL);
+
+ if (desc->outblob_format == TSM_FORMAT_EXTENDED)
+ size = report_size + ext_size;
+ else
+ size = report_size;
+
+ u8 *buf __free(kvfree) = kvzalloc(size, GFP_KERNEL);
+
+ if (desc->outblob_format == TSM_FORMAT_EXTENDED) {
+ struct snp_ext_report_req ext_req = {
+ .data = { .vmpl = desc->privlevel },
+ .certs_address = (__u64)buf + report_size,
+ .certs_len = ext_size,
+ };
+ memcpy(&ext_req.data.user_data, desc->inblob, desc->inblob_len);
+
+ struct snp_guest_request_ioctl input = {
+ .msg_version = 1,
+ .req_data = (__u64)&ext_req,
+ .resp_data = (__u64)buf,
+ };
Won't the compiler complain about this declaration being after the memcpy()?
+
+ ret = get_ext_report(snp_dev, &input, SNP_KARG);
+ } else {
+ struct snp_report_req req = {
+ .vmpl = desc->privlevel,
+ };
+ memcpy(&req.user_data, desc->inblob, desc->inblob_len);
+
+ struct snp_guest_request_ioctl input = {
+ .msg_version = 1,
+ .req_data = (__u64) &req,
+ .resp_data = (__u64) buf,
+ };
Ditto here.
Thanks,
Tom
+
+ ret = get_report(snp_dev, &input, SNP_KARG);
+ }
+
+ if (ret)
+ return ERR_PTR(ret);
+
+ *outblob_len = size;
+ no_free_ptr(buf);
+ return buf;
+}
+
+static const struct tsm_ops sev_tsm_ops = {
+ .name = KBUILD_MODNAME,
+ .report_new = sev_report_new,
+};
+
+static const struct attribute_group *sev_tsm_attribute_groups[] = {
+ &tsm_default_attribute_group,
+ &tsm_extra_attribute_group,
+ NULL,
+};
+
+static void unregister_sev_tsm(void *data)
+{
+ unregister_tsm(&sev_tsm_ops);
+}
+
static int __init sev_guest_probe(struct platform_device *pdev)
{
struct snp_secrets_page_layout *layout;
@@ -842,6 +915,14 @@ static int __init sev_guest_probe(struct platform_device *pdev)
snp_dev->input.resp_gpa = __pa(snp_dev->response);
snp_dev->input.data_gpa = __pa(snp_dev->certs_data);
+ ret = register_tsm(&sev_tsm_ops, &pdev->dev, sev_tsm_attribute_groups);
+ if (ret)
+ goto e_free_cert_data;
+
+ ret = devm_add_action_or_reset(&pdev->dev, unregister_sev_tsm, NULL);
+ if (ret)
+ goto e_free_cert_data;
+
ret = misc_register(misc);
if (ret)
goto e_free_cert_data;