linux-kernel - Re: 2.6.29 pat issue

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]

Date:	Thu, 05 Feb 2009 17:11:41 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Thomas Hellstrom <thellstrom@...are.com>
Cc:	"Pallipadi\, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	"Siddha\, Suresh B" <suresh.b.siddha@...el.com>
Subject: Re: 2.6.29 pat issue

Thomas Hellstrom <thellstrom@...are.com> writes:

> Indeed, it's crucial to keep the mappings consistent, but failure to do so is a
> kernel driver bug, it should never be the result of invalid user data.

It easily can be.  Think of an X server mmaping frame buffers. Or other
device bars.

> There are other more common kernel bugs that can be even worse and hang / crash
> the system. For example using uninitialized spinlocks, writing to kfreed memory
> etc. There is code in the kernel to detect these as well, but this code is
> behind debug defines.

There are cpu errata on almost every cpu in existence that come into play
if you have the cacheabilty attributes wrong on a page.  CPUs have been known
to do very weird things when you hit those errata.  At the best of it you
are no longer running on a deterministic machine, at the worst of it you
crash the cpu.

> IMHO checking each vm_insert_pfn() for caching attribute correctness is not
> something that should be enabled by default, due to the CPU overhead. Production
> drivers should never violate this.

If it is a problem the implementation should become more efficient.  Userspace
as well as drivers can generate these mappings so even with a perfect driver
you cannot guarantee that someone else does not have that area of memory
mapped differently.

Eric
--
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/