security/lockdown: Write-protect WP_RO

Allow to write protect only the WP_RO region in case of enabled VBOOT.
One can either lock the boot device in VERSTAGE early if VBOOT is enabled,
or late in RAMSTAGE. Both options have their downsides as explained below.

Lock early if you don't trust the code that's stored in the writeable
flash partition. This prevents write-protecting the MRC cache, which
is written in ramstage. In case the contents of the MRC cache are
corrupted this can lead to system instability or trigger unwanted code
flows inside the firmware.

Lock late if you trust the code that's stored in the writeable
flash partition. This allows write-protecting the MRC cache, but
if a vulnerability is found in the code of the writeable partition
an attacker might be able to overwrite the whole flash as it hasn't
been locked yet.

Change-Id: I72c3e1a0720514b9b85b0433944ab5fb7109b2a2
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Christian Walter <christian.walter@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32705
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/include/boot_device.h b/src/include/boot_device.h
index 31464624b9..d5237cd45a 100644
--- a/src/include/boot_device.h
+++ b/src/include/boot_device.h
@@ -65,7 +65,7 @@ void boot_device_init(void);
 /*
  * Restrict read/write access to the bootmedia using platform defined rules.
  */
-#if CONFIG(BOOTMEDIA_LOCK_NONE)
+#if CONFIG(BOOTMEDIA_LOCK_NONE) || (CONFIG(BOOTMEDIA_LOCK_IN_VERSTAGE) && ENV_RAMSTAGE)
 static inline void boot_device_security_lockdown(void) {}
 #else
 void boot_device_security_lockdown(void);