linux-kernel - Re: [RFC PATCH] restrict /dev/mem to idle io memory ranges

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: <CAPcyv4hagUwc3AJuDHvBy+YR1Khv+5uUL0HZawO9R0r-EZLVHg@mail.gmail.com>
Date:	Fri, 20 Nov 2015 12:26:13 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-nvdimm <linux-nvdimm@...1.01.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Will Deacon <will.deacon@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH] restrict /dev/mem to idle io memory ranges

On Fri, Nov 20, 2015 at 12:12 PM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Fri, Nov 20, 2015 at 09:31:33AM -0800, Dan Williams wrote:
>> This effectively promotes IORESOURCE_BUSY to IORESOURCE_EXCLUSIVE
>> semantics by default.  If userspace really believes it is safe to access
>> the memory region it can also perform the extra step of disabling an
>> active driver.  This protects device address ranges with read side
>> effects and otherwise directs userspace to use the driver.
>
> I'm happy with this as long as we retain the option to disable this
> new behaviour.
>
> The reason being, when developing a driver, it is _very_ useful to
> be able to poke around in the device's (and system memory) address
> spaces with tools like devmem2 to work out what's going on when
> things go wrong.
>
> To put it another way, I think it's a good idea to disable access to
> these regions on production systems, but for driver development, we
> want to retain the ability to poke around in physical address space
> in any way we so desire.
>

Sounds ok to me, but I do think it's a good idea to default it to the
same value as STRICT_DEVMEM.  Perhaps:

bool "Filter I/O access to /dev/mem" if EXPERT
default STRICT_DEVMEM

When this in do we even need IORESOURCE_EXCLUSIVE?  It's barely used.
--
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/