On Mon, 2011-01-31 at 13:40 -0600, Scott Wood wrote:
> On Mon, 31 Jan 2011 14:16:00 -0500
> Steve Best <sfb...@us.ibm.com> wrote:
>
> > Provide devmem_is_allowed() routine to restrict access to kernel
> > memory from userspace.
> > Set CONFIG_STRICT_DEVMEM config option to switch on checking.
> >
> > Signed-off-by: Steve Best <sfb...@us.ibm.com>
> >
> > diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
> > index 2d38a50..6805d5d 100644
> > --- a/arch/powerpc/Kconfig.debug
> > +++ b/arch/powerpc/Kconfig.debug
> > @@ -299,4 +299,16 @@ config PPC_EARLY_DEBUG_CPM_ADDR
> > platform probing is done, all platforms selected must
> > share the same address.
> >
> > +config STRICT_DEVMEM
> > + def_bool y
> > + prompt "Filter access to /dev/mem"
> > + ---help---
> > + This option restricts access to /dev/mem. If this option is
> > + disabled, you allow userspace access to all memory, including
> > + kernel and userspace memory. Accidental memory access is likely
> > + to be disastrous.
> > + Memory access is required for experts who want to debug the
> > kernel.
> > +
> > + If you are unsure, say Y.
> > +
> > endmenu
> > diff --git a/arch/powerpc/include/asm/page.h
> > b/arch/powerpc/include/asm/page.h
> > index 53b64be..f225032 100644
> > --- a/arch/powerpc/include/asm/page.h
> > +++ b/arch/powerpc/include/asm/page.h
> > @@ -262,6 +262,11 @@ extern void copy_user_page(void *to, void *from,
> > unsigned long vaddr,
> > struct page *p);
> > extern int page_is_ram(unsigned long pfn);
> >
> > +static inline int devmem_is_allowed(unsigned long pfn)
> > +{
> > + return 0;
> > +}
> > +
>
> I don't see how this is a sane thing to turn on by default (you're not
> restricting it, BTW -- you're completely disabling it with that
> implementation of devmem_is_allowed). It will break anything that
> uses /dev/mem to access I/O,
could you expand on what I/O depends on /dev/mem, so I can take
that into account?
> possibly including desktoppy stuff like X
> servers,
you are right just found out that X needs to access it. will
take that into account
> as well as lots of stuff that goes on in embedded setups.
could you explain more about what needs access to /dev/mem in
the embedded setups?
>
> You need to be root to access /dev/mem, and root has plenty of
> other options for causing "disastrous" results. You don't just stumble
> onto /dev/mem by accident.
>
> -Scott
-Steve
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