linux-kernel - Re: [PATCH v3 0/3] Handle memmap and mem kernel options in boot stage kaslr

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Date:   Sat, 29 Apr 2017 07:02:51 +0800
From:   Baoquan He <bhe@...hat.com>
To:     YASUAKI ISHIMATSU <yasu.isimatu@...il.com>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org, dyoung@...hat.com,
        douly.fnst@...fujitsu.com, dan.j.williams@...el.com
Subject: Re: [PATCH v3 0/3] Handle memmap and mem kernel options in boot
 stage kaslr

On 04/27/17 at 03:57pm, YASUAKI ISHIMATSU wrote:
> Hi Baoquan,
> 
> 
> On 04/26/2017 06:16 AM, Baoquan He wrote:
> > People reported kernel panic occurs during system boots up with mem boot option.
> > After checking code, several problems are found about memmap= and mem= in boot stage
> > kaslr.
> > 
> > *) In commit f28442497b5c ("x86/boot: Fix KASLR and memmap= collision"), only one memmap
> >    entry is considered and only the last one if multiple memmap entries are specified.
> > 
> 
> > *) mem= and memmap=nn[KMG] are not considered yet. They are used to limit max address
> >    of system. Kernel can't be randomized to be above the limit.
> 
> I confirmed that mem= works correctly.
> 
> Tested-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>

Thanks for your effort, Yasuaki Ishimatsu!

> 
> 
> > 
> > *) kernel-parameters.txt doesn't tell the updated behaviour of memmap=.
> > 
> > This patchset tries to solve above issues, and it sits on top of
> > tip:x86/boot branch.
> > 
> > Changelog
> > 
> > v2->v3:
> > No functionality change in this round.
> > a)Use local static variable insted of global variable
> >   mem_avoid_memmap_index in patch 1/3.
> > b)Fix a typo in patch 3/3.
> > 
> > v1->v2:
> > a)The original patch 1/4 has been put in tip:x86/boot and no update,
> >   so it's not included in this post.
> > b)Use patch log Ingo reorganized.
> > c)lib/ctype.c and lib/cmdline.c are needed for kaslr.c, while those
> >   EXPORT_SYMBOL(x) contained caused failure of build on 32-bit allmodconfig:
> >   ......
> >   ld: -r and -shared may not be used together
> >   scripts/Makefile.build:294: recipe for target 'arch/x86/boot/compressed/kaslr.o' failed
> >   ......
> >   Disabling the symbol exporting removes the build failure.
> > d)Use dynamic allocation to allocate memory to contain copied kernel cmdline
> >   buffer, it's implemented in include/linux/decompress/mm.h.
> > 
> > 
> > 
> > Baoquan He (3):
> >   KASLR: Parse all memmap entries in cmdline
> >   KASLR: Handle memory limit specified by memmap and mem option
> >   Documentation/kernel-parameters.txt: Update 'memmap=' option
> >     description
> > 
> >  Documentation/admin-guide/kernel-parameters.txt |   9 ++
> >  arch/x86/boot/compressed/cmdline.c              |   2 +-
> >  arch/x86/boot/compressed/kaslr.c                | 183 +++++++++++++++---------
> >  arch/x86/boot/string.c                          |   8 ++
> >  4 files changed, 136 insertions(+), 66 deletions(-)
> >