Date: Thu, 5 Jan 2017 15:16:05 -0800 From: Thomas Garnier <thgarnie@...gle.com> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Andy Lutomirski <luto@...nel.org>, Arjan van de Ven <arjan@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave@...1.net>, Chen Yucong <slaoub@...il.com>, Paul Gortmaker <paul.gortmaker@...driver.com>, Andrew Morton <akpm@...ux-foundation.org>, Masahiro Yamada <yamada.masahiro@...ionext.com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Anna-Maria Gleixner <anna-maria@...utronix.de>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, Michael Ellerman <mpe@...erman.id.au>, Juergen Gross <jgross@...e.com>, Richard Weinberger <richard@....at>, X86 ML <x86@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com> Subject: Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location On Thu, Jan 5, 2017 at 3:05 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote: > On Thu, Jan 5, 2017 at 12:18 PM, Andy Lutomirski <luto@...nel.org> wrote: >> >> Hmm. I bet that if we preset the accessed bits in all the segments >> then we don't need it to be writable in general. > > I'm not sure that this is architecturally safe. > > IIRC, we do mark the IDT read-only - but that one we started doing due > to the f00f bug, so we knew it was ok. I'm not sure you can do the > same with the GDT/LDT. > I started testing a variant that make the GDT remapping read-only by default and writeable only for LTR. Everything works fine, even hibernation. I need to do more testing though on different architectures. To be on the safe side, I could separate the read-only part in a separate patch so we can easily remove it if extended testing show something. > Linus -- Thomas
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