[PATCH v3 6/6] powerpc/fsl_booke/kaslr: rename kaslr-booke32.rst to kaslr-booke.rst and add 64bit part
From: Jason Yan <yanaijie@huawei.com>
Date: 2020-02-06 02:59:51
Also in:
lkml
Subsystem:
documentation, the rest · Maintainers:
Jonathan Corbet, Linus Torvalds
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 <yanaijie@huawei.com>
Cc: Scott Wood <oss@buserror.net>
Cc: Diana Craciun <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Christophe Leroy <redacted>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <redacted>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Kees Cook <redacted>
---
.../{kaslr-booke32.rst => kaslr-booke.rst} | 35 ++++++++++++++++---
1 file changed, 31 insertions(+), 4 deletions(-)
rename Documentation/powerpc/{kaslr-booke32.rst => kaslr-booke.rst} (59%)
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..42121fed8249 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 as 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