linux-kernel - Re: [PATCH 07/13] kexec: Implementation of new syscall kexec_file

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Date:	Fri, 13 Jun 2014 16:00:28 +0800
From:	WANG Chao <chaowang@...hat.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
	mjg59@...f.ucam.org, bhe@...hat.com, jkosina@...e.cz,
	greg@...ah.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, ebiederm@...ssion.com, hpa@...or.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 07/13] kexec: Implementation of new syscall
 kexec_file_load

On 06/13/14 at 09:50am, Borislav Petkov wrote:
> On Mon, Jun 09, 2014 at 11:41:37AM -0400, Vivek Goyal wrote:
> > IIUC, COMMAND_LINE_SIZE gives max limits of running kernel and it does
> > not tell us anything about command line size supported by kernel being
> > loaded.
> 
> Whatever you do, you do need a sane default because even querying the
> boot protocol is not reliable as the to-be-loaded kernel's boot protocol
> might be manipulated too, before signing (who knows what people do
> in the wild).

Make sense.

> 
> So having a sane, unconditional fallback COMMAND_LINE_SIZE from the
> first kernel is a must, methinks.

By greping for COMMAND_LINE_SIZE for different arch, I think 8K being
the fallback, in general, is good for now and the future:

alpha/include/uapi/asm/setup.h
4:#define COMMAND_LINE_SIZE     256

arm/include/uapi/asm/setup.h
19:#define COMMAND_LINE_SIZE 1024

avr32/include/uapi/asm/setup.h
14:#define COMMAND_LINE_SIZE 256

cris/include/uapi/asm/setup.h
4:#define COMMAND_LINE_SIZE     256

frv/include/uapi/asm/setup.h
15:#define COMMAND_LINE_SIZE       512

ia64/include/uapi/asm/setup.h
4:#define COMMAND_LINE_SIZE     2048

m32r/include/uapi/asm/setup.h
8:#define COMMAND_LINE_SIZE       512

m68k/include/uapi/asm/setup.h
14:#define COMMAND_LINE_SIZE 256

mips/include/uapi/asm/setup.h
4:#define COMMAND_LINE_SIZE     4096

parisc/include/uapi/asm/setup.h
4:#define COMMAND_LINE_SIZE     1024

powerpc/include/uapi/asm/setup.h
4:#define COMMAND_LINE_SIZE     2048

s390/include/uapi/asm/setup.h
9:#define COMMAND_LINE_SIZE     4096

um/include/asm/setup.h
8:#define COMMAND_LINE_SIZE 4096

x86/include/asm/setup.h
6:#define COMMAND_LINE_SIZE 2048

xtensa/include/uapi/asm/setup.h
14:#define COMMAND_LINE_SIZE    256

c6x/include/uapi/asm/setup.h
4:#define COMMAND_LINE_SIZE   1024

microblaze/include/uapi/asm/setup.h
14:#define COMMAND_LINE_SIZE    256

mn10300/include/uapi/asm/param.h
16:#define COMMAND_LINE_SIZE 256

score/include/uapi/asm/setup.h
4:#define COMMAND_LINE_SIZE     256

tile/include/uapi/asm/setup.h
18:#define COMMAND_LINE_SIZE    2048

arc/include/asm/setup.h
15:#define COMMAND_LINE_SIZE 256

arm64/include/uapi/asm/setup.h
24:#define COMMAND_LINE_SIZE    2048
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