break;
if (p->end < addr)
continue;
- if (p->flags & IORESOURCE_BUSY &&
- p->flags & IORESOURCE_EXCLUSIVE) {
+ /*
+ * A resource is exclusive if IORESOURCE_EXCLUSIVE is set
+ * or CONFIG_IO_STRICT_DEVMEM is enabled and the
+ * resource is busy.
+ */
+ if ((p->flags & IORESOURCE_BUSY) == 0)
+ continue;
+ if (IS_ENABLED(CONFIG_IO_STRICT_DEVMEM)
+ || p->flags & IORESOURCE_EXCLUSIVE) {
err = 1;
break;
}
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.