| Message ID | 20151122035707.9313.59919.stgit@dwillia2-desk3.jf.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sat, Nov 21, 2015 at 7:57 PM, Dan Williams <dan.j.williams@intel.com> 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. > > Persistent memory presents a large "mistake surface" to /dev/mem as now > accidental writes can corrupt a filesystem. > > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Kees Cook <keescook@chromium.org> > Cc: Russell King <linux@arm.linux.org.uk> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Signed-off-by: Dan Williams <dan.j.williams@intel.com> Acked-by: Kees Cook <keescook@chromium.org> Thanks! -Kees > --- > kernel/resource.c | 3 +++ > lib/Kconfig.debug | 23 ++++++++++++++++++++--- > 2 files changed, 23 insertions(+), 3 deletions(-) > > diff --git a/kernel/resource.c b/kernel/resource.c > index f150dbbe6f62..03a8b09f68a8 100644 > --- a/kernel/resource.c > +++ b/kernel/resource.c > @@ -1498,6 +1498,9 @@ int iomem_is_exclusive(u64 addr) > break; > if (p->end < addr) > continue; > + if (IS_ENABLED(CONFIG_IO_STRICT_DEVMEM) > + && p->flags & IORESOURCE_BUSY) > + break; > if (p->flags & IORESOURCE_BUSY && > p->flags & IORESOURCE_EXCLUSIVE) { > err = 1; > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index ad85145d0047..be47f99fb191 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -1866,9 +1866,26 @@ config STRICT_DEVMEM > enabled, even in this case there are restrictions on /dev/mem > use due to the cache aliasing requirements. > > + If this option is switched on, and IO_STRICT_DEVMEM=n, the /dev/mem > + file only allows userspace access to PCI space and the BIOS code and > + data regions. This is sufficient for dosemu and X and all common > + users of /dev/mem. > + > + If in doubt, say Y. > + > +config IO_STRICT_DEVMEM > + bool "Filter I/O access to /dev/mem" > + depends on STRICT_DEVMEM > + default STRICT_DEVMEM > + ---help--- > + If this option is disabled, you allow userspace (root) access to all > + io-memory regardless of whether a driver is actively using that > + range. Accidental access to this is obviously disastrous, but > + specific access can be used by people debugging kernel drivers. > + > If this option is switched on, the /dev/mem file only allows > - userspace access to PCI space and the BIOS code and data regions. > - This is sufficient for dosemu and X and all common users of > - /dev/mem. > + userspace access to *idle* io-memory ranges (see /proc/iomem) This > + may break traditional users of /dev/mem (dosemu, legacy X, etc...) > + if the driver using a given range cannot be disabled. > > If in doubt, say Y. >
diff --git a/kernel/resource.c b/kernel/resource.c index f150dbbe6f62..03a8b09f68a8 100644 --- a/kernel/resource.c +++ b/kernel/resource.c @@ -1498,6 +1498,9 @@ int iomem_is_exclusive(u64 addr) break; if (p->end < addr) continue; + if (IS_ENABLED(CONFIG_IO_STRICT_DEVMEM) + && p->flags & IORESOURCE_BUSY) + break; if (p->flags & IORESOURCE_BUSY && p->flags & IORESOURCE_EXCLUSIVE) { err = 1; diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index ad85145d0047..be47f99fb191 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1866,9 +1866,26 @@ config STRICT_DEVMEM enabled, even in this case there are restrictions on /dev/mem use due to the cache aliasing requirements. + If this option is switched on, and IO_STRICT_DEVMEM=n, the /dev/mem + file only allows userspace access to PCI space and the BIOS code and + data regions. This is sufficient for dosemu and X and all common + users of /dev/mem. + + If in doubt, say Y. + +config IO_STRICT_DEVMEM + bool "Filter I/O access to /dev/mem" + depends on STRICT_DEVMEM + default STRICT_DEVMEM + ---help--- + If this option is disabled, you allow userspace (root) access to all + io-memory regardless of whether a driver is actively using that + range. Accidental access to this is obviously disastrous, but + specific access can be used by people debugging kernel drivers. + If this option is switched on, the /dev/mem file only allows - userspace access to PCI space and the BIOS code and data regions. - This is sufficient for dosemu and X and all common users of - /dev/mem. + userspace access to *idle* io-memory ranges (see /proc/iomem) This + may break traditional users of /dev/mem (dosemu, legacy X, etc...) + if the driver using a given range cannot be disabled. If in doubt, say Y.
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. Persistent memory presents a large "mistake surface" to /dev/mem as now accidental writes can corrupt a filesystem. Cc: Arnd Bergmann <arnd@arndb.de> Cc: Kees Cook <keescook@chromium.org> Cc: Russell King <linux@arm.linux.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Dan Williams <dan.j.williams@intel.com> --- kernel/resource.c | 3 +++ lib/Kconfig.debug | 23 ++++++++++++++++++++--- 2 files changed, 23 insertions(+), 3 deletions(-)