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From: Ingo Molnar <mingo@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@suse.de>, Baoquan He <bhe@redhat.com>,
	Yinghai Lu <yinghai@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	"x86@kernel.org" <x86@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	"H.J. Lu" <hjl.tools@gmail.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Andy Lutomirski <luto@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/5] x86, KASLR: Drop CONFIG_RANDOMIZE_BASE_MAX_OFFSET
Date: Fri, 22 Apr 2016 09:16:12 +0200	[thread overview]
Message-ID: <20160422071612.GA6819@gmail.com> (raw)
In-Reply-To: <CAGXu5j+n3GdKV9xHHTa1siD=C_+63oUm5Rby-qXCvVAD1Og9Fw@mail.gmail.com>


* Kees Cook <keescook@chromium.org> wrote:

> >> +       Since the kernel is built using 2GB addressing,
> >
> > Does that try to refer to the 1G kernel and 1G fixmap pagetable
> > mappings? I.e., level2_kernel_pgt and level2_fixmap_pgt in
> > arch/x86/kernel/head_64.S?
> 
> The "2GB addressing" part is in reference to:
> 
>        -mcmodel=kernel
>            Generate code for the kernel code model.  The kernel runs in the
>            negative 2 GB of the address space.  This model has to be used for
>            Linux kernel code.

On x86-64 this is a special GCC compiler small memory model, it is called the 
'kernel code model', which is rather generic and no 'real name' ever stuck.

Due to RIP-relative addressing and the sign-extension of 48 bit virtual addresses, 
this allows nearly as compact kernel code and (static) kernel data definitions as 
a 32-bit kernel would allow.

The (positive) 0-4GB virtual memory range has similar advantages, but is of course 
frequently used by user-space code. Negative addresses are reserved for the kernel 
only.

Thanks,

	Ingo

  reply	other threads:[~2016-04-22  7:16 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-20 20:55 [PATCH 0/5] x86, boot: clean up KASLR code (step 2) Kees Cook
2016-04-20 20:55 ` [PATCH 1/5] x86, KASLR: Update description for decompressor worst case size Kees Cook
2016-04-21 14:47   ` Borislav Petkov
2016-04-21 20:04     ` Kees Cook
2016-04-22  3:13       ` Baoquan He
2016-04-22  7:41   ` Ingo Molnar
2016-04-22  9:45   ` [tip:x86/boot] x86/KASLR: " tip-bot for Baoquan He
2016-04-20 20:55 ` [PATCH 2/5] x86, KASLR: Drop CONFIG_RANDOMIZE_BASE_MAX_OFFSET Kees Cook
2016-04-21 17:44   ` Borislav Petkov
2016-04-21 18:13     ` Kees Cook
2016-04-22  7:16       ` Ingo Molnar [this message]
2016-04-22  9:43         ` Borislav Petkov
2016-04-22  9:45   ` [tip:x86/boot] x86/KASLR: " tip-bot for Baoquan He
2016-04-20 20:55 ` [PATCH 3/5] x86, boot: Clean up things used by decompressors Kees Cook
2016-04-22  9:46   ` [tip:x86/boot] x86/boot: " tip-bot for Kees Cook
2016-04-20 20:55 ` [PATCH 4/5] x86, boot: Make memcpy handle overlaps Kees Cook
2016-04-22  7:49   ` Ingo Molnar
2016-04-22 22:18     ` Kees Cook
2016-04-22  7:56   ` Ingo Molnar
2016-04-22  9:46   ` [tip:x86/boot] x86/boot: Make memcpy() " tip-bot for Kees Cook
2016-04-22 21:05     ` Lasse Collin
2016-04-22 22:01       ` Kees Cook
2016-04-20 20:55 ` [PATCH 5/5] x86, KASLR: Warn when KASLR is disabled Kees Cook
2016-04-22  9:47   ` [tip:x86/boot] x86/KASLR: " tip-bot for Kees Cook
2016-04-22  7:43 ` [PATCH 0/5] x86, boot: clean up KASLR code (step 2) Ingo Molnar
2016-04-22 15:39   ` Kees Cook

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