linux-kernel - Re: [PATCH 0/4] Handle memmap and mem kernel options in boot stage kaslr

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Date:   Thu, 20 Apr 2017 21:59:47 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, keescook@...omium.org,
        dave.jiang@...el.com, dan.j.williams@...el.com, hpa@...or.com,
        tglx@...utronix.de, dyoung@...hat.com
Subject: Re: [PATCH 0/4] Handle memmap and mem kernel options in boot stage
 kaslr

On 04/18/17 at 02:51pm, Ingo Molnar wrote:
> 
> * Baoquan He <bhe@...hat.com> wrote:
> 
> > On 04/18/17 at 11:47am, Ingo Molnar wrote:
> > > 
> > > * Baoquan He <bhe@...hat.com> 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.
> > > > 
> > > > *) kernel-parameters.txt doesn't tell the updated behaviour of memmap=.
> > > > 
> > > > This patchset tries to solve above issues.
> > > > 
> > > > Baoquan He (4):
> > > >   param: Move function next_arg to lib/cmdline.c for later reuse
> > > >   KASLR: Parse all memmap entries in cmdline
> > > >   KASLR: Handle memory limit specified by memmap and mem option
> > > >   doc: Update description about memmap option in kernel-parameter.txt
> > > > 
> > > >  Documentation/admin-guide/kernel-parameters.txt |   9 ++
> > > >  arch/x86/boot/compressed/cmdline.c              |   2 +-
> > > >  arch/x86/boot/compressed/kaslr.c                | 161 ++++++++++++++----------
> > > >  arch/x86/boot/string.c                          |   8 ++
> > > >  include/linux/kernel.h                          |   1 +
> > > >  kernel/params.c                                 |  52 --------
> > > >  lib/cmdline.c                                   |  57 +++++++++
> > > >  7 files changed, 172 insertions(+), 118 deletions(-)
> > > 
> > > I ported this series to tip:x86/boot (please post future versions against that), 
> > > and beyond a trivial conflict with e820entry => e820_entry, it fails to 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
> > > 
> > > ... which could be due to bad relocations, but I've not dug any further.
> > 
> > Thanks, Ingo!
> > 
> > I will find a x86_32 system to try allmodconfig.
> 
> No need, on a 64-bit system just do:
> 
> 	make ARCH=i386 allmodconfig
> 
> and build the kernel the regular way.

Sorry for late update. I tried on a x86 64 system with "make ARCH=i386
allmodconfig", and saw the ld warning.  I added a '-r' after -pie, the
building passed. Seems including lib/ctype.c or lib/cmdline.c caused
this. Will dig further to see what's going on.

ifeq ($(CONFIG_X86_32),y)      
LDFLAGS += $(call ld-option, -pie -r) $(call ld-option, --no-dynamic-linker)
else

Thanks
Baoquan