DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 85B2F4E4D2
Date: Fri, 7 Jul 2017 11:07:59 +0800
From: Baoquan He <bhe@redhat.com>
To: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        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
Message-ID: <20170707030759.GA2343@x1>
References: <20170706083106.GA21796@hori1.linux.bs1.fc.nec.co.jp>
 <20170706145727.GB3080@codeblueprint.co.uk>
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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.