[PATCH 3/4] efi/libstub: Measure into CC protocol if TCG2 protocol is absent

Ard Biesheuvel
2024-03-04T10:44:25Z

From: Ard Biesheuvel <ardb@kernel.org>

To accommodate confidential compute VMs that expose the simplified CC
measurement protocol instead of the full-blown TCG2 one, fall back to
the former if the latter does not exist.

The CC protocol was designed to be used in this manner, which is why the
types and prototypes have been kept the same where possible. So reuse
the existing code, and only deviate from the TCG2 code path where
needed.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
drivers/firmware/efi/libstub/efi-stub-helper.c | 67 +++++++++++++++-----
drivers/firmware/efi/libstub/efistub.h | 3 +
2 files changed, 53 insertions(+), 17 deletions(-)

diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index 0dbc9d3f4abd..21f4567324f6 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -223,44 +223,77 @@ static efi_status_t efi_measure_tagged_event(unsigned long load_addr,
unsigned long load_size,
enum efistub_event_type event)
{
+ union {
+ efi_status_t
+ (__efiapi *hash_log_extend_event)(void *, u64, efi_physical_addr_t,
+ u64, const union efistub_event *);
+ struct { u32 hash_log_extend_event; } mixed_mode;
+ } method;
struct efistub_measured_event *evt;
int size = struct_size(evt, tagged_event_data,
events[event].event_data_len);
efi_guid_t tcg2_guid = EFI_TCG2_PROTOCOL_GUID;
efi_tcg2_protocol_t *tcg2 = NULL;
+ union efistub_event ev;
efi_status_t status;
+ void *protocol;

efi_bs_call(locate_protocol, &tcg2_guid, NULL, (void **)&tcg2);
if (tcg2) {
- status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, size,
- (void **)&evt);
- if (status != EFI_SUCCESS)
- goto fail;
-
- evt->event_data.tcg2_data = (struct efi_tcg2_event){
+ ev.tcg2_data = (struct efi_tcg2_event){
.event_size = size,
- .event_header.header_size = sizeof(evt->event_data.tcg2_data.event_header),
+ .event_header.header_size = sizeof(ev.tcg2_data.event_header),
.event_header.header_version = EFI_TCG2_EVENT_HEADER_VERSION,
.event_header.pcr_index = events[event].pcr_index,
.event_header.event_type = EV_EVENT_TAG,
};
+ protocol = tcg2;
+ method.hash_log_extend_event =
+ (void *)efi_table_attr(tcg2, hash_log_extend_event);
+ } else {
+ efi_guid_t cc_guid = EFI_CC_MEASUREMENT_PROTOCOL_GUID;
+ efi_cc_protocol_t *cc = NULL;

- evt->tagged_event_id = events[event].event_id;
- evt->tagged_event_data_size = events[event].event_data_len;
-
- memcpy(evt->tagged_event_data, events[event].event_data,
- events[event].event_data_len);
+ efi_bs_call(locate_protocol, &cc_guid, NULL, (void **)&cc);
+ if (!cc)
+ return EFI_UNSUPPORTED;

- status = efi_call_proto(tcg2, hash_log_extend_event, 0,
- load_addr, load_size, &evt->event_data.tcg2_data);
- efi_bs_call(free_pool, evt);
+ ev.cc_data = (struct efi_cc_event){
+ .event_size = size,
+ .event_header.header_size = sizeof(ev.cc_data.event_header),
+ .event_header.header_version = EFI_CC_EVENT_HEADER_VERSION,
+ .event_header.event_type = EV_EVENT_TAG,
+ };

+ status = efi_call_proto(cc, map_pcr_to_mr_index,
+ events[event].pcr_index,
+ &ev.cc_data.event_header.mr_index);
if (status != EFI_SUCCESS)
goto fail;
- return EFI_SUCCESS;
+
+ protocol = cc;
+ method.hash_log_extend_event =
+ (void *)efi_table_attr(cc, hash_log_extend_event);
}

- return EFI_UNSUPPORTED;
+ status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, size, (void **)&evt);
+ if (status != EFI_SUCCESS)
+ goto fail;
+
+ evt->event_data = ev;
+ evt->tagged_event_id = events[event].event_id;
+ evt->tagged_event_data_size = events[event].event_data_len;
+
+ memcpy(evt->tagged_event_data, events[event].event_data,
+ events[event].event_data_len);
+
+ status = efi_fn_call(&method, hash_log_extend_event, protocol, 0,
+ load_addr, load_size, &evt->event_data);
+ efi_bs_call(free_pool, evt);
+
+ if (status == EFI_SUCCESS)
+ return EFI_SUCCESS;
+
fail:
efi_warn("Failed to measure data for event %d: 0x%lx\n", event, status);
return status;
diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index d621bfb719c4..4bf9a76796b7 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -954,8 +954,11 @@ union efi_cc_protocol {
} mixed_mode;
};

+static_assert(sizeof(efi_tcg2_event_t) == sizeof(efi_cc_event_t));
+
union efistub_event {
efi_tcg2_event_t tcg2_data;
+ efi_cc_event_t cc_data;
};

struct efistub_measured_event {
--
2.44.0.278.ge034bb2e1d-goog