[v2,5/5] virt: sevguest: Add TSM_REPORTS support for SNP_{GET, GET_EXT}_REPORT
Commit Message
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@alien8.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Dionna Glaze <dionnaglaze@google.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/virt/coco/sev-guest/Kconfig | 1
drivers/virt/coco/sev-guest/sev-guest.c | 81 +++++++++++++++++++++++++++++++
2 files changed, 82 insertions(+)
Comments
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@alien8.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Dionna Glaze <dionnaglaze@google.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.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.
Jeremi
> +{
> + struct snp_guest_dev *snp_dev = dev_get_drvdata(dev);
> + const int report_size = SZ_16K;
> + 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,
> + };
> +
> + 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,
> + };
> +
> + 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;
>
On Mon, Aug 14, 2023 at 12:43:38AM -0700, Dan Williams wrote:
> +static u8 *sev_report_new(struct device *dev, const struct tsm_desc *desc,
> + size_t *outblob_len)
> +{
> +
> + u8 *buf __free(kvfree) = kvzalloc(size, GFP_KERNEL);
> +
> +
> + *outblob_len = size;
> + no_free_ptr(buf);
> + return buf;
This seems broken, no_free_ptr(x) is basically xchg(X, NULL) (except no
atomics). So the above would end up being:
return NULL;
What you want to write is somehting like:
return no_free_ptr(buf);
or, a convenient shorthand:
return_ptr(buf);
Peter Zijlstra wrote:
> On Mon, Aug 14, 2023 at 12:43:38AM -0700, Dan Williams wrote:
> > +static u8 *sev_report_new(struct device *dev, const struct tsm_desc *desc,
>
> > + size_t *outblob_len)
> > +{
>
> > +
> > + u8 *buf __free(kvfree) = kvzalloc(size, GFP_KERNEL);
> > +
>
> > +
> > + *outblob_len = size;
> > + no_free_ptr(buf);
> > + return buf;
>
> This seems broken, no_free_ptr(x) is basically xchg(X, NULL) (except no
> atomics). So the above would end up being:
>
> return NULL;
>
> What you want to write is somehting like:
>
> return no_free_ptr(buf);
>
> or, a convenient shorthand:
>
> return_ptr(buf);
>
Oh, I indeed did not realize that no_free_ptr() had side effects beyond
canceling the free when the variable goes out of scope. Will switch to
return_ptr().
On Mon, Aug 14, 2023 at 09:25:06AM -0700, Dan Williams wrote:
> Peter Zijlstra wrote:
> > On Mon, Aug 14, 2023 at 12:43:38AM -0700, Dan Williams wrote:
> > > +static u8 *sev_report_new(struct device *dev, const struct tsm_desc *desc,
> >
> > > + size_t *outblob_len)
> > > +{
> >
> > > +
> > > + u8 *buf __free(kvfree) = kvzalloc(size, GFP_KERNEL);
> > > +
> >
> > > +
> > > + *outblob_len = size;
> > > + no_free_ptr(buf);
> > > + return buf;
> >
> > This seems broken, no_free_ptr(x) is basically xchg(X, NULL) (except no
> > atomics). So the above would end up being:
> >
> > return NULL;
> >
> > What you want to write is somehting like:
> >
> > return no_free_ptr(buf);
> >
> > or, a convenient shorthand:
> >
> > return_ptr(buf);
> >
>
> Oh, I indeed did not realize that no_free_ptr() had side effects beyond
> canceling the free when the variable goes out of scope. Will switch to
> return_ptr().
Indeed -- ideally no_free_ptr() would be combined with __must_check, but
I'm not immediately sure how to pull that off. Let me stick that on the
to-do list.
@@ -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,
@@ -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;
+ 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,
+ };
+
+ 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,
+ };
+
+ 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;