vboot: allow for dynamic work buffers

The vboot library currently relies on link-time known
address and sizes of the work buffer.  Not all platforms
can provide such semantics. Therefore, add an option
to use cbmem for the work buffer. This implies such platforms
can only do verification of the firmware after main memory
has been initialized.

Change-Id: If0b0f6b2a187b5c1fb56af08b6cb384a935be096
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/10157
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/vendorcode/google/chromeos/vboot2/Kconfig

@@ -101,3 +101,13 @@ config VBOOT_BOOT_LOADER_INDEX
 	help
 	  This is the index of the bootloader component in the verified
 	  firmware block.
+
+config VBOOT_DYNAMIC_WORK_BUFFER
+	bool "Vboot's work buffer is dynamically allocated."
+	default n
+	depends on VBOOT_VERIFY_FIRMWARE
+	help
+	  This option is used when there isn't enough pre-main memory
+	  ram to allocate the vboot work buffer. That means vboot verification
+	  is after memory init and requires main memory to back the work
+	  buffer.

src/vendorcode/google/chromeos/vboot2/common.c

@@ -18,6 +18,7 @@
  */
 
 #include <cbfs.h>
+#include <cbmem.h>
 #include <console/console.h>
 #include <reset.h>
 #include "../chromeos.h"
@@ -25,14 +26,23 @@
 #include "../vboot_handoff.h"
 #include "misc.h"
 
+static const size_t vb_work_buf_size = 16 * KiB;
+
 struct vb2_working_data * const vboot_get_working_data(void)
 {
-	return (struct vb2_working_data *)_vboot2_work;
+	if (IS_ENABLED(CONFIG_VBOOT_DYNAMIC_WORK_BUFFER))
+		/* cbmem_add() does a cbmem_find() first. */
+		return cbmem_add(CBMEM_ID_VBOOT_WORKBUF, vb_work_buf_size);
+	else
+		return (struct vb2_working_data *)_vboot2_work;
 }
 
 size_t vb2_working_data_size(void)
 {
-	return _vboot2_work_size;
+	if (IS_ENABLED(CONFIG_VBOOT_DYNAMIC_WORK_BUFFER))
+		return vb_work_buf_size;
+	else
+		return _vboot2_work_size;
 }
 
 void *vboot_get_work_buffer(struct vb2_working_data *wd)