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

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Date:   Thu, 27 Apr 2017 15:57:25 -0400
From:   YASUAKI ISHIMATSU <yasu.isimatu@...il.com>
To:     Baoquan He <bhe@...hat.com>, mingo@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     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

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,
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(-)
>