linux-kernel - Re: [PATCH] x86, kdump: Fix efi=noruntime NULL pointer dereference

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Date:   Thu, 09 Aug 2018 09:33:30 +0200
From:   Mike Galbraith <efault@....de>
To:     Dave Young <dyoung@...hat.com>
Cc:     Baoquan He <bhe@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        lkml <linux-kernel@...r.kernel.org>, kexec@...ts.infradead.org
Subject: Re: [PATCH] x86, kdump: Fix efi=noruntime NULL pointer dereference

On Thu, 2018-08-09 at 12:21 +0800, Dave Young wrote:
> Hi Mike,
> 
> Thanks for the patch!
> On 08/08/18 at 04:03pm, Mike Galbraith wrote:
> > When booting with efi=noruntime, we call efi_runtime_map_copy() while
> > loading the kdump kernel, and trip over a NULL efi.memmap.map.  Avoid
> > that and a useless allocation when the only mapping we can use (1:1)
> > is not available.
> 
> At first glance, efi_get_runtime_map_size should return 0 in case
> noruntime.

What efi does internally at unmap time is to leave everything except
efi.mmap.map untouched, setting it to NULL and turning off EFI_MEMMAP,
rendering efi.mmap.map accessors useless/unsafe without first checking
EFI_MEMMAP.

	-Mike