linux-kernel - Re: [PATCH v3 02/11] x86/kexec: Add extra pointers to transition page table PGD, PUD, PMD and PTE

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20130109184253.GA5150@host-192-168-1-59.local.net-space.pl>
Date:	Wed, 9 Jan 2013 19:42:53 +0100
From:	Daniel Kiper <daniel.kiper@...cle.com>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	andrew.cooper3@...rix.com, x86@...nel.org, tglx@...utronix.de,
	kexec@...ts.infradead.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel <xen-devel@...ts.xen.org>, konrad.wilk@...cle.com,
	maxim.uvarov@...cle.com, mingo@...hat.com, vgoyal@...hat.com,
	linux-kernel@...r.kernel.org, ebiederm@...ssion.com, hpa@...or.com
Subject: Re: [PATCH v3 02/11] x86/kexec: Add extra pointers to transition
 page table PGD, PUD, PMD and PTE

On Mon, Jan 07, 2013 at 01:05:10PM +0000, Jan Beulich wrote:
> >>> On 07.01.13 at 13:52, Daniel Kiper <daniel.kiper@...cle.com> wrote:
> > On Mon, Jan 07, 2013 at 09:48:20AM +0000, Jan Beulich wrote:
> >> >>> On 04.01.13 at 18:25, Daniel Kiper <daniel.kiper@...cle.com> wrote:
> >> > Right, so where is virtual mapping of control page established?
> >> > I could not find relevant code in SLES kernel which does that.
> >>
> >> In the hypervisor (xen/arch/x86/machine_kexec.c:machine_kexec_load()).
> >> xen/arch/x86/machine_kexec.c:machine_kexec() then simply uses
> >> image->page_list[1].
> >
> > This (xen/arch/x86/machine_kexec.c:machine_kexec_load()) maps relevant
> > page (allocated earlier by dom0) in hypervisor fixmap area. However,
> > it does not make relevant mapping in transition page table which
> > leads to crash when %cr3 is switched from Xen page table to
> > transition page table.
>
> That indeed could explain _random_ failures - the fixmap entries
> get created with _PAGE_GLOBAL set, i.e. don't get flushed with
> the CR3 write unless CR4.PGE is clear.

This does not matter. As I stated earlier virtual mapping is wrong.
relocate_kernel() is mapped at its virtual address in Linux kernel
instead of control page at its virtual address in Xen hypervisor.
I tested SLES kernel once again. It does not work.

> And I don't see how your allocation of intermediate page tables
> would help: You wouldn't know where the mapping of the control
> page lives until you're actually in the early relocate_kernel code.

Right. Allocation itself is not a solution for this problem.
It should be acompanied by code which establishes transition
page table in relocate_kernel() (which is later copied
to control page, i.e. code of relocate_kernel()).

> Or was it that what distinguishes your cloned code from the
> native original?

No, my code is based on native original.
There are some implementation differences.

Daniel
--
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/