linux-kernel - Re: [RFC PATCH 2/2] x86/sev: Disable jump tables in SEV startup code

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: <CAHk-=wgRQppa6o0G4booOsBteuMCu9twmw05=noScFJLoY=ybQ@mail.gmail.com>
Date: Mon, 27 Jan 2025 09:09:44 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, 
	Ard Biesheuvel <ardb@...nel.org>, Ingo Molnar <mingo@...nel.org>, 
	Tom Lendacky <thomas.lendacky@....com>, Nathan Chancellor <nathan@...nel.org>
Subject: Re: [RFC PATCH 2/2] x86/sev: Disable jump tables in SEV startup code

On Mon, 27 Jan 2025 at 03:43, Ard Biesheuvel <ardb+git@...gle.com> wrote:
>
> +# jump tables are emitted using absolute references in non-PIC code
> +# so they cannot be used in the early SEV startup code
> +CFLAGS_core.o += -fno-jump-tables

I can confirm that this looks like it fixes the problem for my
particular config.

Is the SEV code the only thing that needs this? And on the other hand,
isn't it just a _part_ of core.c that needs this? Maybe the "_head"
parts should be in a separate file?

I'm looking at (for example) arch/x86/mm/mem_encrypt_identity.c and
arch/x86/kernel/head64.c, and it looks like it really should have that
-fno-jump-tables thing too.

It just randomly may not have any switch tables or other things that
makes the compiler generate that code pattern.

(I did this just by a grep, maybe there's something else protecting
those files that I just didn't see)

           Linus