security: enhance DEFAULT_MMAP_MIN_ADDR description

Got burned by setting the proposed default of 65536
across all Debian archs.

Thus proposing to be more specific on which archs you may
set this. Also propose a value for arm and friends that
doesn't break sshd.

Reword to mention working archs ia64 and ppc64 too.

Signed-off-by: maximilian attems <max@stro.at>
Cc: Martin Michlmayr <tbm@cyrius.com>
Cc: Gordon Farquharson <gordonfarquharson@gmail.com>
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

diff --git a/security/Kconfig b/security/Kconfig
index 5dfc206..49b51f9 100644 (file)
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -113,10 +113,12 @@ config SECURITY_DEFAULT_MMAP_MIN_ADDR
          from userspace allocation.  Keeping a user from writing to low pages
          can help reduce the impact of kernel NULL pointer bugs.
 
-         For most users with lots of address space a value of 65536 is
-         reasonable and should cause no problems.  Programs which use vm86
-         functionality would either need additional permissions from either
-         the LSM or the capabilities module or have this protection disabled.
+         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 would either need additional
+         permissions from either the LSM or the capabilities module or have
+         this protection disabled.
 
          This value can be changed after boot using the
          /proc/sys/vm/mmap_min_addr tunable.