linux-kernel - Re: [PATCH v2 0/2] x86/boot/KASLR: Code bug fix about kernel virtual address randomization

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Message-ID: <20170630061423.GA13433@dhcp-128-65.nay.redhat.com>
Date:   Fri, 30 Jun 2017 14:14:23 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        hpa@...or.com
Subject: Re: [PATCH v2 0/2] x86/boot/KASLR: Code bug fix about kernel virtual
 address randomization

On 06/27/17 at 08:39pm, Baoquan He wrote:
> People complained that crashkernel high doesn't work when kaslr code
> compiled in but add 'nokaslr' to diable it. Kexec has the same
> phenomenon.

This is a regression, with 4.12* kernel kexec reboot fails always on
my desktop pc now without kaslr being enabled.

> 
> The root cause is a code bug which assigned the original loading address
> of kernel to the local variable 'virt_addr' which represents the offset
> of kernel virtual address randmoization. As we know, kernel can be loaded
> to anywhere under 64T physically, this wrong assignment could cause kernel
> relocation handling of x86 64 error if no kaslr is taken.
> 
> The v1 post can be found here:
>   x86/boot/KASLR: Skip relocation handling in no kaslr case
>   https://patchwork.kernel.org/patch/9807789/
> 
> In v2, Ingo suggested that we should add a judgement to check if 'virt_addr'
> is randomized to make kernel beyond the kernel mapping area. This checking
> can let us know the error but not reset to firmware quietly as it does now.
> 
> Baoquan He (2):
>   x86/boot/KASLR: Add checking for the offset of kernel virtual address
>     randomization
>   x86/boot/KASLR: Fix the wrong assignment to 'virt_addr'
> 
>  arch/x86/boot/compressed/kaslr.c | 3 ---
>  arch/x86/boot/compressed/misc.c  | 6 ++++--
>  arch/x86/boot/compressed/misc.h  | 2 --
>  3 files changed, 4 insertions(+), 7 deletions(-)
> 
> -- 
> 2.5.5
>