From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Fleming Subject: Re: [PATCH] x86 efi: bugfix interrupt disabling sequence Date: Fri, 20 Sep 2013 16:28:59 +0100 Message-ID: <20130920152859.GC21381@console-pimps.org> References: <1379525333-4373-1-git-send-email-bemk@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1379525333-4373-1-git-send-email-bemk-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: linux-efi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Bart Kuivenhoven Cc: matt.fleming-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org, tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org, mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, jcm-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, msalter-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org List-Id: linux-efi@vger.kernel.org On Wed, 18 Sep, at 07:28:53PM, Bart Kuivenhoven wrote: > The problem in efi_main was that the idt was cleared before the > interrupts were disabled. > > The UEFI spec states that interrupts aren't used so this shouldn't be > too much of a problem. Peripherals however don't necessarily know about > this and thus might cause interrupts to happen anyway. Even if > ExitBootServices() has been called. > > This means there is a risk of an interrupt being triggered while the IDT > register is nullified and the interrupt bit hasn't been cleared, > allowing for a triple fault. Just to be clear, you haven't witnessed a triple fault, correct? > This patch fixes this by clearing the interrupt bit before the lidt > instruction. I think we can go even further than this and get rid of all of the IDT code in the EFI boot stub. The kernel maintains its own IDT anyway. -- Matt Fleming, Intel Open Source Technology Center