linux-kernel - Re: [RFC] ELF Relocatable x86 and x86

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <m18xlz8zdo.fsf@ebiederm.dsl.xmission.com>
Date:	Tue, 08 Aug 2006 01:23:15 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Horms <horms@...ge.net.au>
Cc:	"H. Peter Anvin" <hpa@...or.com>, vgoyal@...ibm.com,
	fastboot@...l.org, linux-kernel@...r.kernel.org,
	Jan Kratochvil <lace@...kratochvil.net>,
	Magnus Damm <magnus.damm@...il.com>,
	Linda Wang <lwang@...hat.com>
Subject: Re: [RFC] ELF Relocatable x86 and x86_64 bzImages

Horms <horms@...ge.net.au> writes:

> On Mon, Aug 07, 2006 at 09:32:23PM -0700, H. Peter Anvin wrote:
>> Horms wrote:
>> >
>> >I also agree that it is non-intitive. But I wonder if a cleaner
>> >fix would be to remove CONFIG_PHYSICAL_START all together. Isn't
>> >it just a work around for the kernel not being relocatable, or
>> >are there uses for it that relocation can't replace?
>> >
>> 
>> Yes, booting with the 2^n existing bootloaders.
>
> Ok, I must be confused then. I though CONFIG_PHYSICAL_START was
> introduced in order to allow an alternative address to be provided for
> kdump, and that previously it was hard-coded to some
> architecture-specific value.
>
> What I was really getting as is if it needs to be configurable at
> compile time or not. Obviously there needs to be some sane default
> regardless.

CONFIG_PHYSICAL_START has had 2 uses.
1) To allow a kernel to run a completely different address for use
   with kexec on panic.
2) To allow the kernel to be better aligned for better performance.

For maintenance reasons I propose we introduce CONFIG_PHYSICAL_ALIGN.
Which will round our load address up to the nearest aligned address
and run the kernel there.  That is roughly what I am doing on x86_64
at this point.

s/CONFIG_PHYSICAL_START/CONFIG_PHYSICAL_ALIGN/ gives me well defined
behavior and allows the alignment optimization without getting into 
weird semantics.

Before CONFIG_PHYSICAL_START we _always_ ran the arch/i386 kernel
where it was loaded and I assumed we always would.  Since people have
realized better aligned kernels can run better this assumption became
false.  Going to CONFIG_PHYSICAL_ALIGN allows us to return to the
simple assumption of always running the kernel where it is loaded
modulo a little extra alignment.

Eric
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/