All of lore.kernel.org
 help / color / mirror / Atom feed
From: "H. Peter Anvin" <hpa@zytor.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: whissi@whissi.de, ak@linux.intel.com, keescook@chromium.org,
	Baoquan He <bhe@redhat.com>,
	x86@kernel.org, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org,
	mingo@redhat.com, kumagai-atsushi@mxc.nes.nec.co.jp,
	ebiederm@xmission.com, tglx@linutronix.de
Subject: Re: [resend Patch v3 1/2] kaslr: check if kernel location is changed
Date: Wed, 08 Oct 2014 08:09:59 -0700	[thread overview]
Message-ID: <543553C7.9010906@zytor.com> (raw)
In-Reply-To: <20141001135237.GA13689@redhat.com>

On 10/01/2014 06:52 AM, Vivek Goyal wrote:
> 
> Hi Peter,
> 
> I think there is some confusion. I will try to clarify.
> 
> If we have 32bit signed overflow, we will not have a functional kernel.
> And that's the message we get when we try to kexec with
> CONFIG_RANDOMIZE_BASE=y.
> 

And how does that happen?

> **********************************************************************
> [  340.709078] kexec: Starting new kernel
> early console in decompress_kernel
> KASLR disabled by default...
> 
> Decompressing Linux... Parsing ELF...
> 
> Performing relocations...
> 32-bit relocation outside of kernel!
> 
> 
>  -- System halted
> *****************************************************************
> 
> We realized that kexec tries to load kernel at higher physical addresses
> and that can lead to problmes.
> 
> Currently for x86_64, handle_relocations() will perform relocations if
> kernel is not loaded at LOAD_PHYSICAL_ADDR. I think this does not work for
> all the cases and kerenl can not be loaded anywhere in the physical address
> space. And that's why we run into issues with kexec.
> 
> My understanding is that we introduce handle_relcoations() i386 style
> because of RANDOMIZE_BASE. If that's the case, one possible solution
> is that perform relocations only if ranodmize base logic has chosen
> a different load location for kernel than where boot loader loaded
> it. Otherwise don't do anything.
> 
> In case of kexec/kdump, we will pass "nokaslr" to second kernel forcing
> it to do nothing and let the kernel run where it was loaded by bootloader.
> And in that case handle_relocations() should not do any relocations and
> that should allow kernel to be loaded anywhere in physical memory on
> x86_64.
> 

Sorry... this makes no sense.

For x86-64, there is no direct connection between the physical and
virtual address spaces that the kernel runs in...

	-hpa



_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

WARNING: multiple messages have this Message-ID (diff)
From: "H. Peter Anvin" <hpa@zytor.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Baoquan He <bhe@redhat.com>,
	linux-kernel@vger.kernel.org, tglx@linutronix.de,
	mingo@redhat.com, x86@kernel.org, keescook@chromium.org,
	ak@linux.intel.com, ebiederm@xmission.com,
	kexec@lists.infradead.org, whissi@whissi.de,
	kumagai-atsushi@mxc.nes.nec.co.jp, stable@vger.kernel.org
Subject: Re: [resend Patch v3 1/2] kaslr: check if kernel location is changed
Date: Wed, 08 Oct 2014 08:09:59 -0700	[thread overview]
Message-ID: <543553C7.9010906@zytor.com> (raw)
In-Reply-To: <20141001135237.GA13689@redhat.com>

On 10/01/2014 06:52 AM, Vivek Goyal wrote:
> 
> Hi Peter,
> 
> I think there is some confusion. I will try to clarify.
> 
> If we have 32bit signed overflow, we will not have a functional kernel.
> And that's the message we get when we try to kexec with
> CONFIG_RANDOMIZE_BASE=y.
> 

And how does that happen?

> **********************************************************************
> [  340.709078] kexec: Starting new kernel
> early console in decompress_kernel
> KASLR disabled by default...
> 
> Decompressing Linux... Parsing ELF...
> 
> Performing relocations...
> 32-bit relocation outside of kernel!
> 
> 
>  -- System halted
> *****************************************************************
> 
> We realized that kexec tries to load kernel at higher physical addresses
> and that can lead to problmes.
> 
> Currently for x86_64, handle_relocations() will perform relocations if
> kernel is not loaded at LOAD_PHYSICAL_ADDR. I think this does not work for
> all the cases and kerenl can not be loaded anywhere in the physical address
> space. And that's why we run into issues with kexec.
> 
> My understanding is that we introduce handle_relcoations() i386 style
> because of RANDOMIZE_BASE. If that's the case, one possible solution
> is that perform relocations only if ranodmize base logic has chosen
> a different load location for kernel than where boot loader loaded
> it. Otherwise don't do anything.
> 
> In case of kexec/kdump, we will pass "nokaslr" to second kernel forcing
> it to do nothing and let the kernel run where it was loaded by bootloader.
> And in that case handle_relocations() should not do any relocations and
> that should allow kernel to be loaded anywhere in physical memory on
> x86_64.
> 

Sorry... this makes no sense.

For x86-64, there is no direct connection between the physical and
virtual address spaces that the kernel runs in...

	-hpa



  reply	other threads:[~2014-10-08 15:10 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-30  7:08 [resend Patch v3 1/2] kaslr: check if kernel location is changed Baoquan He
2014-09-30  7:08 ` Baoquan He
2014-09-30  7:08 ` [resend Patch v3 2/2] export the kernel image size KERNEL_IMAGE_SIZE Baoquan He
2014-09-30  7:08   ` Baoquan He
2015-02-02  7:32   ` Baoquan He
2015-02-02  7:32     ` Baoquan He
2015-02-09 20:18     ` Kees Cook
2015-02-09 20:18       ` Kees Cook
2014-09-30 21:21 ` [resend Patch v3 1/2] kaslr: check if kernel location is changed H. Peter Anvin
2014-09-30 21:21   ` H. Peter Anvin
2014-10-01 13:52   ` Vivek Goyal
2014-10-01 13:52     ` Vivek Goyal
2014-10-08 15:09     ` H. Peter Anvin [this message]
2014-10-08 15:09       ` H. Peter Anvin
2014-10-08 19:27       ` Vivek Goyal
2014-10-08 19:27         ` Vivek Goyal
2014-10-11  3:14         ` Baoquan He
2014-10-11  3:14           ` Baoquan He
2014-10-11 10:34           ` H. Peter Anvin
2014-10-11 10:34             ` H. Peter Anvin
2014-10-11 12:38             ` Baoquan He
2014-10-11 12:38               ` Baoquan He
2014-10-11 12:44               ` Baoquan He
2014-10-11 12:44                 ` Baoquan He
2014-10-13 12:52             ` Vivek Goyal
2014-10-13 12:52               ` Vivek Goyal
2014-10-13 15:19               ` Vivek Goyal
2014-10-13 15:19                 ` Vivek Goyal
2014-10-13 15:43                 ` H. Peter Anvin
2014-10-13 15:43                   ` H. Peter Anvin
2014-10-13 17:22                   ` Vivek Goyal
2014-10-13 17:22                     ` Vivek Goyal
2014-10-14 12:49                     ` Vivek Goyal
2014-10-14 12:49                       ` Vivek Goyal
2014-10-15  3:37                       ` Baoquan He
2014-10-15  3:37                         ` Baoquan He
2014-10-15 20:22                         ` Vivek Goyal
2014-10-15 20:22                           ` Vivek Goyal
2014-10-15 20:32                         ` H. Peter Anvin
2014-10-15 20:32                           ` H. Peter Anvin
2014-10-15 23:55                           ` Baoquan He
2014-10-15 23:55                             ` Baoquan He
2014-10-15 23:58                             ` Baoquan He
2014-10-15 23:58                               ` Baoquan He
2014-10-28  5:04                         ` Baoquan He
2014-10-28  5:04                           ` Baoquan He
2014-10-08 14:40   ` Baoquan He
2014-10-08 14:40     ` Baoquan He
2015-01-09  2:09 ` Baoquan He
2015-01-09  2:09   ` Baoquan He

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=543553C7.9010906@zytor.com \
    --to=hpa@zytor.com \
    --cc=ak@linux.intel.com \
    --cc=bhe@redhat.com \
    --cc=ebiederm@xmission.com \
    --cc=keescook@chromium.org \
    --cc=kexec@lists.infradead.org \
    --cc=kumagai-atsushi@mxc.nes.nec.co.jp \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=stable@vger.kernel.org \
    --cc=tglx@linutronix.de \
    --cc=vgoyal@redhat.com \
    --cc=whissi@whissi.de \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.