linux-kernel - Re: [PATCH 9/9] x86/kexec: Use typedef for relocate_kernel

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: <111B7BEE-FDA0-4085-8A97-89EC9DE7A51B@infradead.org>
Date: Tue, 17 Dec 2024 11:06:57 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: Ard Biesheuvel <ardb@...nel.org>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 Eric Biederman <ebiederm@...ssion.com>, David Woodhouse <dwmw@...zon.co.uk>,
 Sourabh Jain <sourabhjain@...ux.ibm.com>,
 Hari Bathini <hbathini@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>,
 Thomas Zimmermann <tzimmermann@...e.de>,
 Andrew Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>,
 Yuntao Wang <ytcoode@...il.com>, David Kaplan <david.kaplan@....com>,
 Tao Liu <ltao@...hat.com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Kai Huang <kai.huang@...el.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
 Breno Leitao <leitao@...ian.org>, Wei Yang <richard.weiyang@...il.com>,
 Rong Xu <xur@...gle.com>,
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
 linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
 Simon Horman <horms@...nel.org>, Dave Young <dyoung@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, bsz@...zon.de, nathan@...nel.org
Subject: Re: [PATCH 9/9] x86/kexec: Use typedef for relocate_kernel_fn function prototype

On 17 December 2024 10:54:19 CET, Ard Biesheuvel <ardb@...nel.org> wrote:
>On Tue, 17 Dec 2024 at 10:42, David Woodhouse <dwmw2@...radead.org> wrote:
>> Hm, I am perfectly happy to believe that my memory is failing me, especially when it comes to specifics of i386 assembler code. But are you also telling me that
>> <https://kernelnewbies.org/FAQ/asmlinkage> is a lie?
>>
>
>It seems wildly out of date, at least.
>
>Commit 96a388de5dc53a8b2 from 2007 removed the asmlinkage definition
>containing regparm(0) from include/asm-i386/linkage.h, and I'm not
>convinced it was ever sound to conflate linkage with calling
>convention like that. Today, asmlinkage evaluates to 'extern "C"' when
>using a C++ compiler, which is also not part of the type.
>
>However, I failed to notice that this just moves code around, and only
>applies to 32-bit in the first place. So I won't waste any more of
>your time obsessing over this.

Too late :)

You've already made me concerned about what the calling convention *is* for relocate_kernel() on i386. Because if asmlinkage doesn't mean regparm(0) any more and the i386 kernel is still built with -mregparm=3, then how does the asm code (which seems to believe all its arguments are on the stack) actually work?

It seems slightly unlikely that kexec on i386 has just been broken since 2007 but I'm not sure I'd completely rule it out.

So now I guess I have to actually build a 32-bit userspace test case and *test* it.

And that means I no longer have any excuse for not doing all the same cleanups in the i386 version of the code that I've done for x86_64...

Thanks for that :)