x86, kaslr: Return location from decompress_kernel

This allows decompress_kernel to return a new location for the kernel to
be relocated to. Additionally, enforces CONFIG_PHYSICAL_START as the
minimum relocation position when building with CONFIG_RELOCATABLE.

With CONFIG_RANDOMIZE_BASE set, the choose_kernel_location routine
will select a new location to decompress the kernel, though here it is
presently a no-op. The kernel command line option "nokaslr" is introduced
to bypass these routines.

Signed-off-by: Kees Cook <keescook@chromium.org>
Link: http://lkml.kernel.org/r/1381450698-28710-3-git-send-email-keescook@chromium.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index fcbb736d55fe..773fc4c077b4 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1975,6 +1975,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
         noapic          [SMP,APIC] Tells the kernel to not make use of any
                         IOAPICs that may be present in the system.
 
+        nokaslr         [X86]
+                        Disable kernel base offset ASLR (Address Space
+                        Layout Randomization) if built into the kernel.
+
         noautogroup     Disable scheduler automatic task group creation.
 
         nobats          [PPC] Do not use BATs for mapping kernel lowmem