linux-kernel - Re: [PATCH] x86/boot/KASLR: exclude EFI_BOOT_SERVICES

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Date:   Fri, 7 Jul 2017 06:11:24 +0000
From:   Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:     Baoquan He <bhe@...hat.com>
CC:     Matt Fleming <matt@...eblueprint.co.uk>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
        "izumi.taku@...fujitsu.com" <izumi.taku@...fujitsu.com>,
        Thomas Garnier <thgarnie@...gle.com>,
        "fanc.fnst@...fujitsu.com" <fanc.fnst@...fujitsu.com>,
        Junichi Nomura <j-nomura@...jp.nec.com>
Subject: Re: [PATCH] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA}
 from KASLR's choice

On Fri, Jul 07, 2017 at 11:07:59AM +0800, Baoquan He wrote:
> On 07/06/17 at 03:57pm, Matt Fleming wrote:
> > On Thu, 06 Jul, at 08:31:07AM, Naoya Horiguchi wrote:
> > > +	for (i = 0; i < nr_desc; i++) {
> > > +		md = (efi_memory_desc_t *)(pmap + (i * e->efi_memdesc_size));
> > > +
> > > +		/*
> > > +		 * EFI_BOOT_SERVICES_{CODE|DATA} are avoided because boot
> > > +		 * services regions could be accessed after ExitBootServices()
> > > +		 * due to the workaround for buggy firmware.
> > > +		 */
> > > +		if (!(md->type == EFI_LOADER_CODE ||
> > > +		      md->type == EFI_LOADER_DATA ||
> > > +		      md->type == EFI_CONVENTIONAL_MEMORY))
> > > +			continue;
> > 
> > Wouldn't it make more sense to *only* use EFI_CONVENTIONAL_MEMORY?
> > 
> > You can't re-use EFI_LOADER_* regions because the kaslr code is run so
> > early in boot that you've no idea if data the kernel will need is in
> > those EFI_LOADER_* regions.
> > 
> > For example, we pass struct setup_data objects inside of
> > EFI_LOADER_DATA regions.
> 
> It doesn't matter because we have tried to avoid those memory setup_data
> resides in in mem_avoid_overlap(). Here discarding EFI_LOADER_* could
> discard the whole regions while setup_data could occupy small part of
> them.

Hi Matt, Baoquan,

I added these three checks to accept any regions corresponding to
E820_TYPE_RAM except EFI_BOOT_SERVICES_*, just thinking of that it's minimum
surprising.  Baoquan gave a good justification on that, so I'll leave it
as-is in next version.

Thanks,
Naoya Horiguchi