linux-kernel - Re: [PATCH v6 RESEND] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

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Message-ID: <20170728095525.y4tuv6aavzfs4ekb@gmail.com>
Date:   Fri, 28 Jul 2017 11:55:25 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, keescook@...omium.org, tglx@...utronix.de,
        hpa@...or.com, izumi.taku@...fujitsu.com, fanc.fnst@...fujitsu.com,
        thgarnie@...gle.com, n-horiguchi@...jp.nec.com
Subject: Re: [PATCH v6 RESEND] x86/boot/KASLR: Restrict kernel to be
 randomized in mirror regions


* Matt Fleming <matt@...eblueprint.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).

Thanks,

	Ingo