Hi Philippe,
On 21/06/2021 23:32, Philippe Mathieu-Daudé wrote:
> Hi Dov,
>
> Minor comments inlined.
>
> On 6/21/21 9:05 PM, Dov Murik wrote:
>> Add the sev_add_kernel_loader_hashes function to calculate the hashes of
>> the kernel/initrd/cmdline and fill a designated OVMF encrypted hash
>> table area. For this to work, OVMF must support an encrypted area to
>> place the data which is advertised via a special GUID in the OVMF reset
>> table.
>>
>> The hashes of each of the files is calculated (or the string in the case
>> of the cmdline with trailing '\0' included). Each entry in the hashes
>> table is GUID identified and since they're passed through the
>> sev_encrypt_flash interface, the hashes will be accumulated by the PSP
>> measurement (SEV_LAUNCH_MEASURE).
>>
>> Co-developed-by: James Bottomley <j...@linux.ibm.com>
>> Signed-off-by: James Bottomley <j...@linux.ibm.com>
>> Signed-off-by: Dov Murik <dovmu...@linux.ibm.com>
>> ---
>> target/i386/sev-stub.c | 5 ++
>> target/i386/sev.c | 121 +++++++++++++++++++++++++++++++++++++++++
>> target/i386/sev_i386.h | 12 ++++
>> 3 files changed, 138 insertions(+)
>>
>> diff --git a/target/i386/sev-stub.c b/target/i386/sev-stub.c
>> index 0227cb5177..2b5e42d644 100644
>> --- a/target/i386/sev-stub.c
>> +++ b/target/i386/sev-stub.c
>> @@ -81,3 +81,8 @@ sev_get_attestation_report(const char *mnonce, Error
>> **errp)
>> error_setg(errp, "SEV is not available in this QEMU");
>> return NULL;
>> }
>> +
>> +bool sev_add_kernel_loader_hashes(KernelLoaderContext *ctx, Error **errp)
>> +{
>> + return false;
>
> Can't happen, so:
>
> g_assert_not_reached();
>
OK, I'll use it.
I guess the comment is relevant to other functions in that file as well
(e.g., sev_encrypt_flash), but I'll leave that to your SEV-housekeeping
series.
>> +}
>> diff --git a/target/i386/sev.c b/target/i386/sev.c
>> index 83df8c09f6..8e3f601bb6 100644
>> --- a/target/i386/sev.c
>> +++ b/target/i386/sev.c
>> @@ -23,6 +23,7 @@
>> #include "qemu/base64.h"
>> #include "qemu/module.h"
>> #include "qemu/uuid.h"
>> +#include "crypto/hash.h"
>> #include "sysemu/kvm.h"
>> #include "sev_i386.h"
>> #include "sysemu/sysemu.h"
>> @@ -83,6 +84,29 @@ typedef struct __attribute__((__packed__)) SevInfoBlock {
>> uint32_t reset_addr;
>> } SevInfoBlock;
>>
>> +#define SEV_HASH_TABLE_RV_GUID "7255371f-3a3b-4b04-927b-1da6efa8d454"
>> +typedef struct __attribute__((__packed__))
>
> The codebase used to use QEMU_PACKED (see "qemu/compiler.h" but
> apparently it isn't enforced.
>
I can use it.
> SevHashTableDescriptor {
>> + /* SEV hash table area guest address */
>> + uint32_t base;
>> + /* SEV hash table area size (in bytes) */
>> + uint32_t size;
>> +} SevHashTableDescriptor;
>> +
>> +/* hard code sha256 digest size */
>> +#define HASH_SIZE 32
>> +
>> +typedef struct __attribute__((__packed__)) SevHashTableEntry {
>> + uint8_t guid[16];
>
> What about using QemuUUID?
>
I agree. I'll use it, coupled with your .data init below.
>> + uint16_t len;
>> + uint8_t hash[HASH_SIZE];
>> +} SevHashTableEntry;
>> +
>> +typedef struct __attribute__((__packed__)) SevHashTable {
>> + uint8_t guid[16];
>> + uint16_t len;
>> + SevHashTableEntry entries[];
>> +} SevHashTable;
>> +
>> static SevGuestState *sev_guest;
>> static Error *sev_mig_blocker;
>>
>> @@ -1077,6 +1101,103 @@ int sev_es_save_reset_vector(void *flash_ptr,
>> uint64_t flash_size)
>> return 0;
>> }
>>
>> +static const uint8_t sev_hash_table_header_guid[] =
>> + UUID_LE(0x9438d606, 0x4f22, 0x4cc9, 0xb4, 0x79, 0xa7, 0x93,
>> + 0xd4, 0x11, 0xfd, 0x21);
>
> Personally I'd have used:
>
> static const QemuUUID sev_hash_table_header_guid = {
> .data = UUID_LE(...);
> };
Yes, I'll use this.
>
> and added qemu_uuid_copy() to complete the API, but that's fine.
I think simple C assignment works for structs (and hence QemuUUID),
something like:
SevHashTable *ht = ...;
ht->guid = sev_hash_table_header_guid;
(where both ht->guid and sev_hash_table_header_guid are QemuUUID.)
>
>> +
>> +static const uint8_t sev_kernel_entry_guid[] =
>> + UUID_LE(0x4de79437, 0xabd2, 0x427f, 0xb8, 0x35, 0xd5, 0xb1,
>> + 0x72, 0xd2, 0x04, 0x5b);
>> +static const uint8_t sev_initrd_entry_guid[] =
>> + UUID_LE(0x44baf731, 0x3a2f, 0x4bd7, 0x9a, 0xf1, 0x41, 0xe2,
>> + 0x91, 0x69, 0x78, 0x1d);
>> +static const uint8_t sev_cmdline_entry_guid[] =
>> + UUID_LE(0x97d02dd8, 0xbd20, 0x4c94, 0xaa, 0x78, 0xe7, 0x71,
>> + 0x4d, 0x36, 0xab, 0x2a);
>> +
>> +static void fill_sev_hash_table_entry(SevHashTableEntry *e, const uint8_t
>> *guid,
>> + const uint8_t *hash, size_t hash_len)
>> +{
>> + memcpy(e->guid, guid, sizeof(e->guid));
>> + e->len = sizeof(*e);
>> + memcpy(e->hash, hash, hash_len);
>> +}
>> +
>> +/*
>> + * Add the hashes of the linux kernel/initrd/cmdline to an encrypted guest
>> page
>> + * which is included in SEV's initial memory measurement.
>> + */
>> +bool sev_add_kernel_loader_hashes(KernelLoaderContext *ctx, Error **errp)
>> +{
>> + uint8_t *data;
>> + SevHashTableDescriptor *area;
>> + SevHashTable *ht;
>> + SevHashTableEntry *e;
>> + uint8_t hash_buf[HASH_SIZE];
>> + uint8_t *hash = hash_buf;
>> + size_t hash_len = sizeof(hash_buf);
>> + int ht_index = 0;
>> + int aligned_len;
>> +
>> + if (!pc_system_ovmf_table_find(SEV_HASH_TABLE_RV_GUID, &data, NULL)) {
>
> If we never use the data_len argument, can we simplify the prototype?
The current uses for the OVMF reset vector GUIDed table is for simple
structs with known length (secret injection page address, SEV-ES reset
address, SEV table of hashes address). But keeping the length there
allows adding variable-sized entries such as strings/blobs.
>
>> + error_setg(errp, "SEV: kernel specified but OVMF has no hash table
>> guid");
>> + return false;
>> + }
>> + area = (SevHashTableDescriptor *)data;
>> +
>> + ht = qemu_map_ram_ptr(NULL, area->base);
>> +
>> + /* Populate the hashes table header */
>> + memcpy(ht->guid, sev_hash_table_header_guid, sizeof(ht->guid));
>> + ht->len = sizeof(*ht);
>> +
>> + /* Calculate hash of kernel command-line */
>> + if (qcrypto_hash_bytes(QCRYPTO_HASH_ALG_SHA256, ctx->cmdline_data,
>> + ctx->cmdline_size,
>> + &hash, &hash_len, errp) < 0) {
>> + return false;
>> + }
>
> Maybe move the qcrypto_hash_bytes() call before filling ht?
(below)
>
>> + e = &ht->entries[ht_index++];
>> + fill_sev_hash_table_entry(e, sev_cmdline_entry_guid, hash, hash_len);
>> +
>> + /* Calculate hash of initrd */
>> + if (ctx->initrd_data) {
>> + if (qcrypto_hash_bytes(QCRYPTO_HASH_ALG_SHA256, ctx->initrd_data,
>> + ctx->initrd_size, &hash, &hash_len, errp) <
>> 0) {
>> + return false;
>> + }
>
> Ah, now I see the pattern. Hmm OK then.
>
But this might change if initrd_hash is no longer optional (see separate
self-reply to this patch). In such a case I'll probably first calculate
all the three hashes, and then fill in the SevHashTable struct.
-Dov
>> + e = &ht->entries[ht_index++];
>> + fill_sev_hash_table_entry(e, sev_initrd_entry_guid, hash, hash_len);
>> + }
>> +
>> + /* Calculate hash of the kernel */
>> + struct iovec iov[2] = {
>> + { .iov_base = ctx->setup_data, .iov_len = ctx->setup_size },
>> + { .iov_base = ctx->kernel_data, .iov_len = ctx->kernel_size }
>> + };
>> + if (qcrypto_hash_bytesv(QCRYPTO_HASH_ALG_SHA256, iov, 2,
>> + &hash, &hash_len, errp) < 0) {
>> + return false;
>> + }
>> + e = &ht->entries[ht_index++];
>> + fill_sev_hash_table_entry(e, sev_kernel_entry_guid, hash, hash_len);
>> +
>> + /* now we have all the possible entries, finalize the hashes table */
>> + ht->len += ht_index * sizeof(*e);
>> + /* SEV len has to be 16 byte aligned */
>> + aligned_len = ROUND_UP(ht->len, 16);
>> + if (aligned_len != ht->len) {
>> + /* zero the excess data so the measurement can be reliably
>> calculated */
>> + memset(&ht->entries[ht_index], 0, aligned_len - ht->len);
>> + }
>> +
>> + if (sev_encrypt_flash((uint8_t *)ht, aligned_len, errp) < 0) {
>> + return false;
>> + }
>> +
>> + return true;
>> +}
>
