Now we support both 32 and 64 bit KASLR for fsl booke. Add document for
64 bit part and rename kaslr-booke32.rst to kaslr-booke.rst.
Signed-off-by: Jason Yan <[email protected]>
Cc: Scott Wood <[email protected]>
Cc: Diana Craciun <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Kees Cook <[email protected]>
---
Documentation/powerpc/index.rst | 2 +-
.../{kaslr-booke32.rst => kaslr-booke.rst} | 35 ++++++++++++++++---
2 files changed, 32 insertions(+), 5 deletions(-)
rename Documentation/powerpc/{kaslr-booke32.rst => kaslr-booke.rst} (59%)
diff --git a/Documentation/powerpc/index.rst b/Documentation/powerpc/index.rst
index 0d45f0fc8e57..3bad36943b22 100644
--- a/Documentation/powerpc/index.rst
+++ b/Documentation/powerpc/index.rst
@@ -20,7 +20,7 @@ powerpc
hvcs
imc
isa-versions
- kaslr-booke32
+ kaslr-booke
mpc52xx
papr_hcalls
pci_iov_resource_on_powernv
diff --git a/Documentation/powerpc/kaslr-booke32.rst b/Documentation/powerpc/kaslr-booke.rst
similarity index 59%
rename from Documentation/powerpc/kaslr-booke32.rst
rename to Documentation/powerpc/kaslr-booke.rst
index 8b259fdfdf03..27a862963242 100644
--- a/Documentation/powerpc/kaslr-booke32.rst
+++ b/Documentation/powerpc/kaslr-booke.rst
@@ -1,15 +1,18 @@
.. SPDX-License-Identifier: GPL-2.0
-===========================
-KASLR for Freescale BookE32
-===========================
+=========================
+KASLR for Freescale BookE
+=========================
The word KASLR stands for Kernel Address Space Layout Randomization.
This document tries to explain the implementation of the KASLR for
-Freescale BookE32. KASLR is a security feature that deters exploit
+Freescale BookE. KASLR is a security feature that deters exploit
attempts relying on knowledge of the location of kernel internals.
+KASLR for Freescale BookE32
+-------------------------
+
Since CONFIG_RELOCATABLE has already supported, what we need to do is
map or copy kernel to a proper place and relocate. Freescale Book-E
parts expect lowmem to be mapped by fixed TLB entries(TLB1). The TLB1
@@ -38,5 +41,29 @@ bit of the entropy to decide the index of the 64M zone. Then we chose a
kernstart_virt_addr
+
+KASLR for Freescale BookE64
+---------------------------
+
+The implementation for Freescale BookE64 is similar to BookE32. One
+difference is that Freescale BookE64 set up a TLB mapping of 1G during
+booting. Another difference is that ppc64 needs the kernel to be
+64K-aligned. So we can randomize the kernel in this 1G mapping and make
+it 64K-aligned. This can save some code to creat another TLB map at early
+boot. The disadvantage is that we only have about 1G/64K = 16384 slots to
+put the kernel in::
+
+ KERNELBASE
+
+ 64K |--> kernel <--|
+ | | |
+ +--+--+--+ +--+--+--+--+--+--+--+--+--+ +--+--+
+ | | | |....| | | | | | | | | |....| | |
+ +--+--+--+ +--+--+--+--+--+--+--+--+--+ +--+--+
+ | | 1G
+ |-----> offset <-----|
+
+ kernstart_virt_addr
+
To enable KASLR, set CONFIG_RANDOMIZE_BASE = y. If KASLR is enable and you
want to disable it at runtime, add "nokaslr" to the kernel cmdline.
--
2.17.2