Re: [PATCH 4/5] common: Add OS anti-rollback grace period

Hi Sean,

On Fri, 11 Aug 2023 at 18:28, seanedmond@linux.microsoft.com wrote:

From: Stephen Carlson stcarlso@microsoft.com

New config CONFIG_FIT_ARBVP_GRACE to add a one unit grace period to OS anti-rollback protection, allowing images with anti-rollback counters exactly one less than the platform value to still be loaded. No update to the platform anti-rollback counter will be performed in this case.

This seems like a grace version rather than a grace period? I'm not sure if that is a better name, but I might imagine a grace period of one month, for example.

Signed-off-by: Stephen Carlson stcarlso@microsoft.com

boot/Kconfig | 10 ++++++++++ boot/image-fit-sig.c | 7 ++++++- 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/boot/Kconfig b/boot/Kconfig index e08c274b7c..cd16bb8e53 100644 --- a/boot/Kconfig +++ b/boot/Kconfig @@ -112,6 +112,16 @@ config FIT_ARBP when a platform needs to retire previous versions of FIT images due to security flaws and prevent devices from being reverted to them.

+config FIT_ARBP_GRACE

•   bool "Enable FIT Anti rollback grace period"
  

•   depends on FIT_ARBP
  

•   default n
  

•   help
  

•     Enables a one unit grace period for FIT image anti-rollback protection,
  

•     where anti-rollback protection will still accept a FIT image with an
  

•     anti-rollback version one less than the current number, but will not
  

•     update the platform anti-rollback counter in that case.
  

config FIT_VERBOSE bool "Show verbose messages when FIT images fail" depends on FIT diff --git a/boot/image-fit-sig.c b/boot/image-fit-sig.c index bf3b81a3a3..dc88a4b2cb 100644 --- a/boot/image-fit-sig.c +++ b/boot/image-fit-sig.c @@ -70,6 +70,7 @@ static int fit_image_verify_arbvn(const void *fit, int image_noffset) { u64 image_arbvn; u64 plat_arbvn = 0ULL;

•   u64 target_arbvn;
    struct udevice *dev;
    int ret;
  
  

@@ -85,7 +86,11 @@ static int fit_image_verify_arbvn(const void *fit, int image_noffset) if (ret) return -EIO;

•   if (image_arbvn < plat_arbvn) {
  

•   target_arbvn = plat_arbvn;
  

•   /* Calculate target ARBVN, including grace period if enabled */
  

•   if (CONFIG_IS_ENABLED(FIT_ARBP_GRACE) && plat_arbvn > 0ULL)
  

0

•           target_arbvn = plat_arbvn - 1ULL;
  

•   if (image_arbvn < target_arbvn) {
            return -EPERM;
    } else if (image_arbvn > plat_arbvn) {
            ret = dm_security_arbvn_set(dev, image_arbvn);
  

-- 2.40.0

Regards, Simon