linux-kernel - Re: [PATCH v5 3/9] x86/head: Move early exception panic code into early_fixup

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: <20160402204752.GC2538@pd.tnic>
Date:	Sat, 2 Apr 2016 22:47:52 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	KVM list <kvm@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	xen-devel <Xen-devel@...ts.xen.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v5 3/9] x86/head: Move early exception panic code into
 early_fixup_exception

On Sat, Apr 02, 2016 at 01:13:37PM -0700, Andy Lutomirski wrote:
> Given that I this isn't really a regression with my patches (it
> probably never worked much better on 32-bit and the regs never would
> have shown at all on 64-bit),

You're right. That thing calls printk *and* early_printk, WTF:

#ifdef CONFIG_EARLY_PRINTK

	call early_printk
	...

	call dump_stack

	...

	call __print_symbol

those last two call printk. Great.

> I propose a different approach: make
> printk work earlier.  Something like:
> 
> if (early) {
>     early_printk(args);
> }
> 
> or early_vprintk or whatever.
> 
> If the cost of a branch mattered, this could be alternative-patched
> out later on, but that seems silly.  I also bet that a more sensible
> fallback could be created in which printk would try to use an early
> console if there's no real console.

So how about this:

printk() does

	vprintk_func = this_cpu_read(printk_func);

and that's

DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default

I guess we can make that function be early_printk-something and once
printk is initialized, we overwrite it with vprintk_default.

Elegant and no need for if branches and alternatives.

Hmmm.

-- 
Regards/Gruss,
    Boris.

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