Messages in this thread | | | Date | Fri, 20 Nov 2015 12:45:02 -0800 | Subject | Re: [RFC PATCH] restrict /dev/mem to idle io memory ranges | From | Kees Cook <> |
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On Fri, Nov 20, 2015 at 12:26 PM, Dan Williams <dan.j.williams@intel.com> wrote: > On Fri, Nov 20, 2015 at 12:12 PM, Russell King - ARM Linux > <linux@arm.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.
Let's leave it for now to give us the debugging granularity Russell mentioned. If it turns out it's never used, we can drop it in the future.
-Kees
-- Kees Cook Chrome OS Security
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