This is a note to let you know that I've just added the patch titled
x86/efi: Clarify that reset attack mitigation needs appropriate userspace
to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: x86-efi-clarify-that-reset-attack-mitigation-needs-appropriate-userspace.patch and it can be found in the queue-4.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From a5c03c31af2291f13689d11760c0b59fb70c9a5a Mon Sep 17 00:00:00 2001
From: Matthew Garrett mjg59@google.com Date: Tue, 16 Jan 2018 09:10:02 +0000 Subject: x86/efi: Clarify that reset attack mitigation needs appropriate userspace
From: Matthew Garrett mjg59@google.com
commit a5c03c31af2291f13689d11760c0b59fb70c9a5a upstream.
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 Acked-by: Ard Biesheuvel ard.biesheuvel@linaro.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-efi@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/firmware/efi/Kconfig | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- 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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Patches currently in stable-queue which might be from mjg59@google.com are
queue-4.15/x86-efi-clarify-that-reset-attack-mitigation-needs-appropriate-userspace.patch