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Date: Fri, 28 Jul 2017 18:18:14 +0800
From: Baoquan He <bhe@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>, linux-kernel@vger.kernel.org,
        x86@kernel.org, keescook@chromium.org, tglx@linutronix.de,
        hpa@zytor.com, izumi.taku@jp.fujitsu.com, fanc.fnst@cn.fujitsu.com,
        thgarnie@google.com, n-horiguchi@ah.jp.nec.com
Subject: Re: [PATCH v6 RESEND] x86/boot/KASLR: Restrict kernel to be
 randomized in mirror regions
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 <20170724133410.GC11076@codeblueprint.co.uk>
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On 07/28/17 at 11:55am, Ingo Molnar wrote:
> 
> * Matt Fleming <matt@codeblueprint.co.uk> wrote:
> 
> > On Fri, 21 Jul, at 09:19:56PM, Baoquan He wrote:
> > >
> > > There are places where the efi map is getting and used like this. E.g
> > > in efi_high_alloc() of drivers/firmware/efi/libstub/efi-stub-helper.c.
> > > EFI developers worry the size of efi_memory_desc_t could not be the same
> > > as e->efi_memdesc_size?
> > > 
> > > Hi Matt,
> > > 
> > > Could you help have a look at this?
> > 
> > You're exactly right. The code guards against the size of the
> > efi_memory_desc_t struct changing. The UEFI spec says to traverse the
> > memory map this way.
> 
> This is not obvious and looks pretty ugly as well, and open coded in several 
> places.
> 
> At minimum we should have an efi_memdesc_ptr(efi, i) wrapper inline (or so) that 
> gives us the entry pointer, plus a comment that points out that ->memdesc_size 
> might not be equal to sizeof(efi_memory_memdesc_t).

Seems for_each_efi_memory_desc_in_map() can be used to hide the
calculation and type cast each time for better memmap loop.