linux-kernel - [PATCH v3 6/6] powerpc/fsl_booke/kaslr: rename kaslr-booke32.rst to kaslr-booke.rst and add 64bit part

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Message-ID: <20200206025825.22934-7-yanaijie@huawei.com>
Date:   Thu, 6 Feb 2020 10:58:25 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     <mpe@...erman.id.au>, <linuxppc-dev@...ts.ozlabs.org>,
        <diana.craciun@....com>, <christophe.leroy@....fr>,
        <benh@...nel.crashing.org>, <paulus@...ba.org>,
        <npiggin@...il.com>, <keescook@...omium.org>,
        <kernel-hardening@...ts.openwall.com>, <oss@...error.net>
CC:     <linux-kernel@...r.kernel.org>, <zhaohongjiang@...wei.com>,
        Jason Yan <yanaijie@...wei.com>
Subject: [PATCH v3 6/6] powerpc/fsl_booke/kaslr: rename kaslr-booke32.rst to kaslr-booke.rst and add 64bit part

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@...wei.com>
Cc: Scott Wood <oss@...error.net>
Cc: Diana Craciun <diana.craciun@....com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Christophe Leroy <christophe.leroy@....fr>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Nicholas Piggin <npiggin@...il.com>
Cc: Kees Cook <keescook@...omium.org>
---
 .../{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