linux-kernel - Re: [resend Patch v3 1/2] kaslr: check if kernel location is changed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <543553C7.9010906@zytor.com>
Date:	Wed, 08 Oct 2014 08:09:59 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	keescook@...omium.org, ak@...ux.intel.com, ebiederm@...ssion.com,
	kexec@...ts.infradead.org, whissi@...ssi.de,
	kumagai-atsushi@....nes.nec.co.jp, stable@...r.kernel.org
Subject: Re: [resend Patch v3 1/2] kaslr: check if kernel location is changed

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


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/