From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To: Baoquan He <bhe@redhat.com>
CC: Matt Fleming <matt@codeblueprint.co.uk>,
        Kees Cook <keescook@chromium.org>, LKML <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Ingo Molnar <mingo@kernel.org>,
        "izumi.taku@jp.fujitsu.com" <izumi.taku@jp.fujitsu.com>,
        Thomas Garnier <thgarnie@google.com>,
        "fanc.fnst@cn.fujitsu.com" <fanc.fnst@cn.fujitsu.com>,
        Junichi Nomura <j-nomura@ce.jp.nec.com>
Subject: Re: [PATCH] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA}
 from KASLR's choice
Thread-Topic: [PATCH] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA}
 from KASLR's choice
Thread-Index: AQHS9jI2mWWdXsD8kkSmPgVylBsaHqJGTRmAgADMHICAADM/AA==
Date: Fri, 7 Jul 2017 06:11:24 +0000
Message-ID: <20170707061123.GA32236@hori1.linux.bs1.fc.nec.co.jp>
References: <20170706083106.GA21796@hori1.linux.bs1.fc.nec.co.jp>
 <20170706145727.GB3080@codeblueprint.co.uk> <20170707030759.GA2343@x1>
In-Reply-To: <20170707030759.GA2343@x1>
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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