Some distributions have turned on the reset attack mitigation feature, which is designed to force the platform to clear the contents of RAM if the machine is shut down uncleanly. However, in order for the platform to be able to determine whether the shutdown was clean or not, userspace has to be configured to clear the MemoryOverwriteRequest flag on shutdown - otherwise the firmware will end up clearing RAM on every reboot, which is unnecessarily time consuming. Add some additional clarity to the kconfig text to reduce the risk of systems being configured this way.

Signed-off-by: Matthew Garrett mjg59@google.com Cc: Ard Biesheuvel ard.biesheuvel@linaro.org Cc: linux-efi@vger.kernel.org Cc: stable@vger.kernel.org --- drivers/firmware/efi/Kconfig | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig index 2b4c39fdfa91..86210f75d233 100644 --- a/drivers/firmware/efi/Kconfig +++ b/drivers/firmware/efi/Kconfig @@ -159,7 +159,10 @@ config RESET_ATTACK_MITIGATION using the TCG Platform Reset Attack Mitigation specification. This protects against an attacker forcibly rebooting the system while it still contains secrets in RAM, booting another OS and extracting the - secrets. + secrets. This should only be enabled when userland is configured to + clear the MemoryOverwriteRequest flag on clean shutdown after secrets + have been evicted, since otherwise it will trigger even on clean + reboots.

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