From: Ingo Molnar <mingo@kernel.org>
Subject: Re: x86: PIE support and option to extend KASLR randomization
Date: Fri, 11 Aug 2017 14:41:27 +0200
Message-ID: <20170811124127.kkb5pnkljz4umxuj@gmail.com>
References: <20170810172615.51965-1-thgarnie@google.com>
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Cc: Herbert Xu <herbert@gondor.apana.org.au>,
	"David S . Miller" <davem@davemloft.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
	Matthias Kaehlcke <mka@chromium.org>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Juergen Gross <jgross@suse.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
	Joerg Roedel <joro@8bytes.org>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@suse.de>,
	Brian Gerst <brgerst@gmail.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
	Tejun Heo <tj@kernel.org>, Christoph Lamete
To: Thomas Garnier <thgarnie@google.com>
Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
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In-Reply-To: <20170810172615.51965-1-thgarnie@google.com>


* Thomas Garnier <thgarnie@google.com> wrote:

> Changes:
>  - v2:
>    - Add support for global stack cookie while compiler default to fs without
>      mcmodel=kernel
>    - Change patch 7 to correctly jump out of the identity mapping on kexec load
>      preserve.
> 
> These patches make the changes necessary to build the kernel as Position
> Independent Executable (PIE) on x86_64. A PIE kernel can be relocated below
> the top 2G of the virtual address space. It allows to optionally extend the
> KASLR randomization range from 1G to 3G.

So this:

 61 files changed, 923 insertions(+), 299 deletions(-)

... is IMHO an _awful_ lot of churn and extra complexity in pretty fragile pieces 
of code, to gain what appears to be only ~1.5 more bits of randomization!

Do these changes get us closer to being able to build the kernel as truly position 
independent, i.e. to place it anywhere in the valid x86-64 address space? Or any 
other advantages?

Thanks,

	Ingo