[Xen-devel] [PATCH 7/9] stubdom/grub: send kernel measurements to vTPM

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

This allows a domU with an arbitrary kernel and initrd to take advantage
of the static root of trust provided by a vTPM.

Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
---
 stubdom/Makefile        |  2 +-
 stubdom/grub/Makefile   |  1 +
 stubdom/grub/kexec.c    | 54 +++++++++++++++++++++++++++++++++++++++++++++++++
 stubdom/grub/minios.cfg |  1 +
 4 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/stubdom/Makefile b/stubdom/Makefile
index 4744b79..790b547 100644
--- a/stubdom/Makefile
+++ b/stubdom/Makefile
@@ -399,7 +399,7 @@ grub-upstream: grub-$(GRUB_VERSION).tar.gz
        done
 
 .PHONY: grub
-grub: grub-upstream $(CROSS_ROOT)
+grub: cross-polarssl grub-upstream $(CROSS_ROOT)
        mkdir -p grub-$(XEN_TARGET_ARCH)
        CPPFLAGS="$(TARGET_CPPFLAGS)" CFLAGS="$(TARGET_CFLAGS)" $(MAKE) 
DESTDIR= -C $@ OBJ_DIR=$(CURDIR)/grub-$(XEN_TARGET_ARCH)
 
diff --git a/stubdom/grub/Makefile b/stubdom/grub/Makefile
index d6e3a1e..6bd2c4c 100644
--- a/stubdom/grub/Makefile
+++ b/stubdom/grub/Makefile
@@ -60,6 +60,7 @@ NETBOOT_SOURCES:=$(addprefix netboot/,$(NETBOOT_SOURCES))
 $(BOOT): DEF_CPPFLAGS+=-D__ASSEMBLY__
 
 PV_GRUB_SOURCES = kexec.c mini-os.c
+PV_GRUB_SOURCES += ../polarssl-$(XEN_TARGET_ARCH)/library/sha1.o
 
 SOURCES = $(NETBOOT_SOURCES) $(STAGE2_SOURCES) $(PV_GRUB_SOURCES)
 
diff --git a/stubdom/grub/kexec.c b/stubdom/grub/kexec.c
index b21c91a..cef357e 100644
--- a/stubdom/grub/kexec.c
+++ b/stubdom/grub/kexec.c
@@ -28,7 +28,9 @@
 #include <blkfront.h>
 #include <netfront.h>
 #include <fbfront.h>
+#include <tpmfront.h>
 #include <shared.h>
+#include <byteswap.h>
 
 #include "mini-os.h"
 
@@ -54,6 +56,22 @@ static unsigned long allocated;
 int pin_table(xc_interface *xc_handle, unsigned int type, unsigned long mfn,
               domid_t dom);
 
+#define TPM_TAG_RQU_COMMAND 0xC1
+#define TPM_ORD_Extend 20
+
+struct pcr_extend_cmd {
+       uint16_t tag;
+       uint32_t size;
+       uint32_t ord;
+
+       uint32_t pcr;
+       unsigned char hash[20];
+} __attribute__((packed));
+
+/* Not imported from polarssl's header since the prototype unhelpfully defines
+ * the input as unsigned char, which causes pointer type mismatches */
+void sha1(const void *input, size_t ilen, unsigned char output[20]);
+
 /* We need mfn to appear as target_pfn, so exchange with the MFN there */
 static void do_exchange(struct xc_dom_image *dom, xen_pfn_t target_pfn, 
xen_pfn_t source_mfn)
 {
@@ -117,6 +135,40 @@ int kexec_allocate(struct xc_dom_image *dom, xen_vaddr_t 
up_to)
     return 0;
 }
 
+static void tpm_hash2pcr(struct xc_dom_image *dom, char *cmdline)
+{
+       struct tpmfront_dev* tpm = init_tpmfront(NULL);
+       uint8_t *resp;
+       size_t resplen = 0;
+       struct pcr_extend_cmd cmd;
+
+       /* If all guests have access to a vTPM, it may be useful to replace this
+        * with ASSERT(tpm) to prevent configuration errors from allowing a 
guest
+        * to boot without a TPM (or with a TPM that has not been sent any
+        * measurements, which could allow forging the measurements).
+        */
+       if (!tpm)
+               return;
+
+       cmd.tag = bswap_16(TPM_TAG_RQU_COMMAND);
+       cmd.size = bswap_32(sizeof(cmd));
+       cmd.ord = bswap_32(TPM_ORD_Extend);
+       cmd.pcr = bswap_32(4); // PCR #4 for kernel
+       sha1(dom->kernel_blob, dom->kernel_size, cmd.hash);
+
+       tpmfront_cmd(tpm, (void*)&cmd, sizeof(cmd), &resp, &resplen);
+
+       cmd.pcr = bswap_32(5); // PCR #5 for cmdline
+       sha1(cmdline, strlen(cmdline), cmd.hash);
+       tpmfront_cmd(tpm, (void*)&cmd, sizeof(cmd), &resp, &resplen);
+
+       cmd.pcr = bswap_32(5); // PCR #5 for initrd
+       sha1(dom->ramdisk_blob, dom->ramdisk_size, cmd.hash);
+       tpmfront_cmd(tpm, (void*)&cmd, sizeof(cmd), &resp, &resplen);
+
+       shutdown_tpmfront(tpm);
+}
+
 void kexec(void *kernel, long kernel_size, void *module, long module_size, 
char *cmdline, unsigned long flags)
 {
     struct xc_dom_image *dom;
@@ -151,6 +203,8 @@ void kexec(void *kernel, long kernel_size, void *module, 
long module_size, char
     dom->console_evtchn = start_info.console.domU.evtchn;
     dom->xenstore_evtchn = start_info.store_evtchn;
 
+    tpm_hash2pcr(dom, cmdline);
+
     if ( (rc = xc_dom_boot_xen_init(dom, xc_handle, domid)) != 0 ) {
         grub_printf("xc_dom_boot_xen_init returned %d\n", rc);
         errnum = ERR_BOOT_FAILURE;
diff --git a/stubdom/grub/minios.cfg b/stubdom/grub/minios.cfg
index 40cfa68..8df4909 100644
--- a/stubdom/grub/minios.cfg
+++ b/stubdom/grub/minios.cfg
@@ -1,2 +1,3 @@
 CONFIG_START_NETWORK=n
 CONFIG_SPARSE_BSS=n
+CONFIG_TPMFRONT=y
-- 
1.7.11.7


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