linux-kernel - Re: [PATCH v2 07/15] x86/lib/copy_user_64.S: Convert to ALTERNATIVE

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Date:	Thu, 5 Mar 2015 09:35:19 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	X86 ML <x86@...nel.org>, Andy Lutomirski <luto@...capital.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 07/15] x86/lib/copy_user_64.S: Convert to ALTERNATIVE_2

On Thu, Mar 05, 2015 at 01:32:49AM +0100, Ingo Molnar wrote:
> We could also do a (limited) relink during early bootup, as part of
> the alternatives patching pass in essence: for that we need to stick
> the relocation info into a section and put that into the vmlinux.

Oh, you want us to do our own asm inlining, so to speak, and save us
even a CALL. Well, that would be more involved and saving a single CALL
is making me question the effort.

Also, with shifted virtual addresses at boot time, debuggability becomes
a serious pain because "objdump -D vmlinux" output is worthless all of a
sudden.

For example, even during doing those patches, I had to go and dump
kernel memory to see what actually gets patched in. And without kvm and
the monitor console, I would've had a serious hard time. If you change
larger portions of the kernel at early boot, that might make the whole
endeavor of debugging a serious undertaking. I already dread the moment
when I'd have to look at a kaslr'ed splat.

We'll see.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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