linux-kernel - Re: [PATCH 1/3] x86: Bugfix bit-rot in the calling of legacy_cache

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: <alpine.DEB.2.11.1409302211560.4455@nanos>
Date:	Tue, 30 Sep 2014 22:28:52 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Bryan O'Donoghue <pure.logic@...us-software.ie>
cc:	mingo@...hat.com, davej@...hat.com, hpa@...or.com, hmh@....eng.br,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] x86: Bugfix bit-rot in the calling of
 legacy_cache_size

On Tue, 30 Sep 2014, Bryan O'Donoghue wrote:
>  static void default_init(struct cpuinfo_x86 *c)
>  {
> -#ifdef CONFIG_X86_64
>  	cpu_detect_cache_sizes(c);
> -#else
> +
>  	/* Not much we can do here... */
>  	/* Check if at least it has cpuid */
>  	if (c->cpuid_level == -1) {
> @@ -79,7 +78,6 @@ static void default_init(struct cpuinfo_x86 *c)
>  		else if (c->x86 == 3)
>  			strcpy(c->x86_model_id, "386");
>  	}
> -#endif

What's the exact point of this? This is the default init function
which is for X86_VENDOR_UNKNOWN, right?

>  }
>  
>  static const struct cpu_dev default_cpu = {
> @@ -874,6 +872,15 @@ static void identify_cpu(struct cpuinfo_x86 *c)
>  #endif
>  
>  	/*
> +	 * If c_x86_vendor != X86_VENDOR_UNKNOWN i.e. a known vendor then
> +	 * there's a vendor specific c_init()
> +	 *
> +	 * Even still Intel, AMD and VIA make use of legacy_cache_size which
> +	 * is reachable only through default_init right now

That's nonsense. It's called from cpu_detect_cache_sizes() and that is
called from:

arch/x86/kernel/cpu/amd.c:      cpu_detect_cache_sizes(c);
arch/x86/kernel/cpu/centaur.c:  cpu_detect_cache_sizes(c);
arch/x86/kernel/cpu/common.c:   cpu_detect_cache_sizes(c);
arch/x86/kernel/cpu/cyrix.c:            cpu_detect_cache_sizes(c);
arch/x86/kernel/cpu/transmeta.c:        cpu_detect_cache_sizes(c);

So we have 4 callsites outside of default_init() already. Now you're
adding another one into identify_cpu()

> +	 */
> +	if (this_cpu->c_x86_vendor != X86_VENDOR_UNKNOWN)
> +		default_init(c);

With the consequence that for amd/centaur/cyrix/transmeta
cpu_detect_cache_sizes() is invoked twice for nothing.

So the only CPU vendor c_init() callback which does not call
cpu_detect_cache_sizes() is the Intel one. And therefor we inflict
that call on all others twice. Brilliant solution!

So the proper solution is to add the call to identify_cpu()
unconditionally and remove it from _all_ other call sites, make it
static and be done with it.

Sigh,

	tglx


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/