[PATCH v3 20/22] sev/i386: Introduce sev_add_kernel_loader_hashes for measured linux boot

[Philippe Mathieu-Daudé]

From: Dov Murik <dovmurik@linux.ibm.com>

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 AMD
PSP measurement (SEV_LAUNCH_MEASURE).

Co-developed-by: James Bottomley <jejb@linux.ibm.com>
Signed-off-by: James Bottomley <jejb@linux.ibm.com>
Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210930054915.13252-2-dovmurik@linux.ibm.com>
[PMD: Rebased on top of 0021c4765a6]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 target/i386/sev_i386.h |  12 ++++
 target/i386/sev.c      | 138 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 150 insertions(+)

diff --git a/target/i386/sev_i386.h b/target/i386/sev_i386.h
index 15a959d6174..17031cddd37 100644
--- a/target/i386/sev_i386.h
+++ b/target/i386/sev_i386.h
@@ -23,9 +23,21 @@
 #define SEV_POLICY_DOMAIN       0x10
 #define SEV_POLICY_SEV          0x20
 
+typedef struct SevKernelLoaderContext {
+    char *setup_data;
+    size_t setup_size;
+    char *kernel_data;
+    size_t kernel_size;
+    char *initrd_data;
+    size_t initrd_size;
+    char *cmdline_data;
+    size_t cmdline_size;
+} SevKernelLoaderContext;
+
 int sev_encrypt_flash(uint8_t *ptr, uint64_t len, Error **errp);
 int sev_inject_launch_secret(const char *hdr, const char *secret,
                              uint64_t gpa, Error **errp);
+bool sev_add_kernel_loader_hashes(SevKernelLoaderContext *ctx, Error **errp);
 
 int sev_es_save_reset_vector(void *flash_ptr, uint64_t flash_size);
 void sev_es_set_reset_vector(CPUState *cpu);
diff --git a/target/i386/sev.c b/target/i386/sev.c
index c6d8fc52eb2..91fdf0d4503 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"
@@ -86,6 +87,32 @@ typedef struct __attribute__((__packed__)) SevInfoBlock {
     uint32_t reset_addr;
 } SevInfoBlock;
 
+#define SEV_HASH_TABLE_RV_GUID  "7255371f-3a3b-4b04-927b-1da6efa8d454"
+typedef struct QEMU_PACKED 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 QEMU_PACKED SevHashTableEntry {
+    QemuUUID guid;
+    uint16_t len;
+    uint8_t hash[HASH_SIZE];
+} SevHashTableEntry;
+
+typedef struct QEMU_PACKED SevHashTable {
+    QemuUUID guid;
+    uint16_t len;
+    SevHashTableEntry cmdline;
+    SevHashTableEntry initrd;
+    SevHashTableEntry kernel;
+    uint8_t padding[];
+} SevHashTable;
+
 static SevGuestState *sev_guest;
 static Error *sev_mig_blocker;
 
@@ -1151,6 +1178,117 @@ int sev_es_save_reset_vector(void *flash_ptr, uint64_t 
flash_size)
     return 0;
 }
 
+static const QemuUUID sev_hash_table_header_guid = {
+    .data = UUID_LE(0x9438d606, 0x4f22, 0x4cc9, 0xb4, 0x79, 0xa7, 0x93,
+                    0xd4, 0x11, 0xfd, 0x21)
+};
+
+static const QemuUUID sev_kernel_entry_guid = {
+    .data = UUID_LE(0x4de79437, 0xabd2, 0x427f, 0xb8, 0x35, 0xd5, 0xb1,
+                    0x72, 0xd2, 0x04, 0x5b)
+};
+static const QemuUUID sev_initrd_entry_guid = {
+    .data = UUID_LE(0x44baf731, 0x3a2f, 0x4bd7, 0x9a, 0xf1, 0x41, 0xe2,
+                    0x91, 0x69, 0x78, 0x1d)
+};
+static const QemuUUID sev_cmdline_entry_guid = {
+    .data = UUID_LE(0x97d02dd8, 0xbd20, 0x4c94, 0xaa, 0x78, 0xe7, 0x71,
+                    0x4d, 0x36, 0xab, 0x2a)
+};
+
+/*
+ * 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(SevKernelLoaderContext *ctx, Error **errp)
+{
+    uint8_t *data;
+    SevHashTableDescriptor *area;
+    SevHashTable *ht;
+    uint8_t cmdline_hash[HASH_SIZE];
+    uint8_t initrd_hash[HASH_SIZE];
+    uint8_t kernel_hash[HASH_SIZE];
+    uint8_t *hashp;
+    size_t hash_len = HASH_SIZE;
+    int aligned_len;
+
+    if (!pc_system_ovmf_table_find(SEV_HASH_TABLE_RV_GUID, &data, NULL)) {
+        error_setg(errp,
+                   "SEV: kernel specified but OVMF has no hash table guid");
+        return false;
+    }
+    area = (SevHashTableDescriptor *)data;
+
+    /*
+     * Calculate hash of kernel command-line with the terminating null byte. If
+     * the user doesn't supply a command-line via -append, the 1-byte "\0" will
+     * be used.
+     */
+    hashp = cmdline_hash;
+    if (qcrypto_hash_bytes(QCRYPTO_HASH_ALG_SHA256, ctx->cmdline_data,
+                           ctx->cmdline_size, &hashp, &hash_len, errp) < 0) {
+        return false;
+    }
+    assert(hash_len == HASH_SIZE);
+
+    /*
+     * Calculate hash of initrd. If the user doesn't supply an initrd via
+     * -initrd, an empty buffer will be used (ctx->initrd_size == 0).
+     */
+    hashp = initrd_hash;
+    if (qcrypto_hash_bytes(QCRYPTO_HASH_ALG_SHA256, ctx->initrd_data,
+                           ctx->initrd_size, &hashp, &hash_len, errp) < 0) {
+        return false;
+    }
+    assert(hash_len == HASH_SIZE);
+
+    /* Calculate hash of the kernel */
+    hashp = kernel_hash;
+    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, ARRAY_SIZE(iov),
+                            &hashp, &hash_len, errp) < 0) {
+        return false;
+    }
+    assert(hash_len == HASH_SIZE);
+
+    /*
+     * Populate the hashes table in the guest's memory at the OVMF-designated
+     * area for the SEV hashes table
+     */
+    ht = qemu_map_ram_ptr(NULL, area->base);
+
+    ht->guid = sev_hash_table_header_guid;
+    ht->len = sizeof(*ht);
+
+    ht->cmdline.guid = sev_cmdline_entry_guid;
+    ht->cmdline.len = sizeof(ht->cmdline);
+    memcpy(ht->cmdline.hash, cmdline_hash, sizeof(ht->cmdline.hash));
+
+    ht->initrd.guid = sev_initrd_entry_guid;
+    ht->initrd.len = sizeof(ht->initrd);
+    memcpy(ht->initrd.hash, initrd_hash, sizeof(ht->initrd.hash));
+
+    ht->kernel.guid = sev_kernel_entry_guid;
+    ht->kernel.len = sizeof(ht->kernel);
+    memcpy(ht->kernel.hash, kernel_hash, sizeof(ht->kernel.hash));
+
+    /* When calling sev_encrypt_flash, the length 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->padding, 0, aligned_len - ht->len);
+    }
+
+    if (sev_encrypt_flash((uint8_t *)ht, aligned_len, errp) < 0) {
+        return false;
+    }
+
+    return true;
+}
+
 static void
 sev_register_types(void)
 {
-- 
2.31.1