From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Matthew Garrett <mjg59@coreos.com>

Date: Sun, 9 Aug 2015 15:48:51 -0700

Subject: [PATCH] Add BIOS boot measurement

Measure the on-disk grub core on BIOS systems - unlike UEFI, the firmware

can't do this stage for us.

---

 grub-core/boot/i386/pc/boot.S     | 30 +++++++++++++++++++++++++-

 grub-core/boot/i386/pc/diskboot.S | 44 +++++++++++++++++++++++++++++++++++++++

 2 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/grub-core/boot/i386/pc/boot.S b/grub-core/boot/i386/pc/boot.S

index ea167fe12..c1df86dec 100644

--- a/grub-core/boot/i386/pc/boot.S

+++ b/grub-core/boot/i386/pc/boot.S

@@ -24,11 +24,14 @@

  *  defines for the code go here

  */

+#define TPM 1

+

 	/* Print message string */

 #define MSG(x)	movw $x, %si; call LOCAL(message)

 #define ERR(x)	movw $x, %si; jmp LOCAL(error_message)

 	.macro floppy

+#ifndef TPM

 part_start:

 LOCAL(probe_values):

@@ -85,6 +88,7 @@ fd_probe_error_string:	.asciz "Floppy"

 	movb	MACRO_DOLLAR(79), %ch

 	jmp	LOCAL(final_init)

+#endif

 	.endm

 	.macro scratch

@@ -252,6 +256,7 @@ real_start:

 	/* set %si to the disk address packet */

 	movw	$disk_address_packet, %si

+#ifndef TPM

 	/* check if LBA is supported */

 	movb	$0x41, %ah

 	movw	$0x55aa, %bx

@@ -271,6 +276,7 @@ real_start:

 	andw	$1, %cx

 	jz	LOCAL(chs_mode)

+#endif

 LOCAL(lba_mode):

 	xorw	%ax, %ax

@@ -314,6 +320,9 @@ LOCAL(lba_mode):

 	jmp	LOCAL(copy_buffer)

 LOCAL(chs_mode):

+#ifdef TPM

+	jmp	LOCAL(general_error)

+#else

 	/*

 	 *  Determine the hard disk geometry from the BIOS!

 	 *  We do this first, so that LS-120 IDE floppies work correctly.

@@ -425,7 +434,7 @@ setup_sectors:

 	jc	LOCAL(read_error)

 	movw	%es, %bx

-

+#endif /* TPM */

 LOCAL(copy_buffer):

 	/*

 	 * We need to save %cx and %si because the startup code in

@@ -448,6 +457,25 @@ LOCAL(copy_buffer):

 	popw	%ds

 	popa

+#ifdef TPM

+	pusha

+

+	movw	$0xBB00, %ax		/* TCG_StatusCheck */

+	int	$0x1A

+	test	%eax, %eax

+	jnz	boot			/* No TPM or TPM deactivated */

+

+	movw	$0xBB07, %ax		/* TCG_CompactHashLogExtendEvent */

+	movw	$GRUB_BOOT_MACHINE_KERNEL_ADDR, %di

+	xorl	%esi, %esi

+	movl	$0x41504354, %ebx	/* TCPA */

+	movl	$0x200, %ecx		/* Measure 512 bytes */

+	movl	$0x8, %edx		/* PCR 8 */

+	int	$0x1A

+

+	popa

+#endif

+boot:

 	/* boot kernel */

 	jmp	*(LOCAL(kernel_address))

diff --git a/grub-core/boot/i386/pc/diskboot.S b/grub-core/boot/i386/pc/diskboot.S

index 68d31de0c..f4744ec6f 100644

--- a/grub-core/boot/i386/pc/diskboot.S

+++ b/grub-core/boot/i386/pc/diskboot.S

@@ -19,6 +19,8 @@

 #include <grub/symbol.h>

 #include <grub/machine/boot.h>

+#define TPM 1

+

 /*

  *  defines for the code go here

  */

@@ -53,6 +55,21 @@ _start:

 	/* this sets up for the first run through "bootloop" */

 	movw	$LOCAL(firstlist), %di

+#ifdef TPM

+        /* clear EAX to remove potential garbage */

+	xorl    %eax, %eax

+	/* 8(%di) = number of sectors to read */

+	movw    8(%di), %ax

+

+	/* Multiply number of sectors to read with 512 bytes. EAX is 32bit

+	* which is large enough to hold values of up to 4GB. I doubt there

+	* will ever be a core.img larger than that. ;-) */

+	shll    $9, %eax

+

+	/* write result to bytes_to_measure var */

+	movl    %eax, bytes_to_measure

+#endif

+

 	/* save the sector number of the second sector in %ebp */

 	movl	(%di), %ebp

@@ -290,6 +307,29 @@ LOCAL(copy_buffer):

 /* END OF MAIN LOOP */

 LOCAL(bootit):

+#ifdef TPM

+	pusha

+	movw	$0xBB07, %ax		/* TCG_CompactHashLogExtendEvent */

+

+	movw	$0x0, %bx

+	movw	%bx, %es

+

+	/* We've already measured the first 512 bytes, now measure the rest */

+	xorl	%edi, %edi

+	movw	$(GRUB_BOOT_MACHINE_KERNEL_ADDR + 0x200), %di

+

+	movl	$0x41504354, %ebx	/* EBX = "TCPA" */

+

+	/* %ecx = The length, in bytes, of the buffer to measure  */

+	movl	$bytes_to_measure, %esi

+	movl	(%esi), %ecx

+	xorl	%esi, %esi

+	movl	$0x9, %edx		/* PCR 9 */

+

+	int	$0x1A

+

+	popa

+#endif

 	/* print a newline */

 	MSG(notification_done)

 	popw	%dx	/* this makes sure %dl is our "boot" drive */

@@ -324,6 +364,10 @@ geometry_error_string:	.asciz "Geom"

 read_error_string:	.asciz "Read"

 general_error_string:	.asciz " Error"

+#ifdef TPM

+bytes_to_measure:	.long 0

+#endif

+

 /*

  * message: write the string pointed to by %si

  *