linux-kernel - Re: [PATCH 2/2] x86/boot: increase maximum number of avoided KASLR regions

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Message-ID: <20190206141753.GE7314@zn.tnic>
Date:   Wed, 6 Feb 2019 15:17:53 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Julian Stecklina <jsteckli@...zon.de>
Cc:     Julian Stecklina <js@...en8.de>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        linux-kernel@...r.kernel.org, jschoenh@...zon.de,
        Dave Jiang <dave.jiang@...el.com>,
        Kees Cook <keescook@...omium.org>, Baoquan He <bhe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] x86/boot: increase maximum number of avoided KASLR
 regions

On Wed, Feb 06, 2019 at 01:50:57PM +0100, Julian Stecklina wrote:
> Because at this point, we are not in a good position to handle an
> unlimited amount of regions.

We could save only the regions which are ok to kaslr into. And we do,
apparently:

static struct slot_area slot_areas[MAX_SLOT_AREA];

but I guess there was a reason to do the mem_avoid thing too instead of
collecting only OK ranges directly. Maybe Kees will know.

> As for the choice of "16", I took our usecase and multiplied it by two.
> FWIW, this could be even larger.

Because our kernel is not fat enough huh?

Btw, you missed a spot:

static unsigned long find_random_phys_addr(unsigned long minimum,
                                           unsigned long image_size)
{
        /* Check if we had too many memmaps. */
        if (memmap_too_large) {
                debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
								^^^^^^^^^^^^^
-- 
Regards/Gruss,
    Boris.

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