Security/SELinux: seperate lsm specific mmap_min_addr

Currently SELinux enforcement of controls on the ability to map low memory
is determined by the mmap_min_addr tunable.  This patch causes SELinux to
ignore the tunable and instead use a seperate Kconfig option specific to how
much space the LSM should protect.

The tunable will now only control the need for CAP_SYS_RAWIO and SELinux
permissions will always protect the amount of low memory designated by
CONFIG_LSM_MMAP_MIN_ADDR.

This allows users who need to disable the mmap_min_addr controls (usual reason
being they run WINE as a non-root user) to do so and still have SELinux
controls preventing confined domains (like a web server) from being able to
map some area of low memory.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/security/Kconfig b/security/Kconfig
index d23c839038f0..9c60c346a91d 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -113,6 +113,22 @@ config SECURITY_ROOTPLUG
 
           If you are unsure how to answer this question, answer N.
 
+config LSM_MMAP_MIN_ADDR
+        int "Low address space for LSM to from user allocation"
+        depends on SECURITY && SECURITY_SELINUX
+        default 65535
+        help
+          This is the portion of low virtual memory which should be protected
+          from userspace allocation.  Keeping a user from writing to low pages
+          can help reduce the impact of kernel NULL pointer bugs.
+
+          For most ia64, ppc64 and x86 users with lots of address space
+          a value of 65536 is reasonable and should cause no problems.
+          On arm and other archs it should not be higher than 32768.
+          Programs which use vm86 functionality or have some need to map
+          this low address space will need the permission specific to the
+          systems running LSM.
+
 source security/selinux/Kconfig
 source security/smack/Kconfig
 source security/tomoyo/Kconfig