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From: Jason Yan <yanaijie@huawei.com>
To: <mpe@ellerman.id.au>, <linuxppc-dev@lists.ozlabs.org>,
	<diana.craciun@nxp.com>, <christophe.leroy@c-s.fr>,
	<benh@kernel.crashing.org>, <paulus@samba.org>,
	<npiggin@gmail.com>, <keescook@chromium.org>,
	<kernel-hardening@lists.openwall.com>
Cc: <linux-kernel@vger.kernel.org>, <wangkefeng.wang@huawei.com>,
	<yebin10@huawei.com>, <thunder.leizhen@huawei.com>,
	<jingxiangfeng@huawei.com>, <zhaohongjiang@huawei.com>,
	<oss@buserror.net>, Jason Yan <yanaijie@huawei.com>
Subject: [PATCH v7 12/12] powerpc/fsl_booke/32: Document KASLR implementation
Date: Fri, 20 Sep 2019 17:45:46 +0800
Message-ID: <20190920094546.44948-13-yanaijie@huawei.com> (raw)
In-Reply-To: <20190920094546.44948-1-yanaijie@huawei.com>

Add document to explain how we implement KASLR for fsl_booke32.

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Cc: Diana Craciun <diana.craciun@nxp.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
---
 Documentation/powerpc/kaslr-booke32.rst | 42 +++++++++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 Documentation/powerpc/kaslr-booke32.rst

diff --git a/Documentation/powerpc/kaslr-booke32.rst b/Documentation/powerpc/kaslr-booke32.rst
new file mode 100644
index 000000000000..8b259fdfdf03
--- /dev/null
+++ b/Documentation/powerpc/kaslr-booke32.rst
@@ -0,0 +1,42 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===========================
+KASLR for Freescale BookE32
+===========================
+
+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
+attempts relying on knowledge of the location of kernel internals.
+
+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
+entries are not suitable to map the kernel directly in a randomized
+region, so we chose to copy the kernel to a proper place and restart to
+relocate.
+
+Entropy is derived from the banner and timer base, which will change every
+build and boot. This not so much safe so additionally the bootloader may
+pass entropy via the /chosen/kaslr-seed node in device tree.
+
+We will use the first 512M of the low memory to randomize the kernel
+image. The memory will be split in 64M zones. We will use the lower 8
+bit of the entropy to decide the index of the 64M zone. Then we chose a
+16K aligned offset inside the 64M zone to put the kernel in::
+
+    KERNELBASE
+
+        |-->   64M   <--|
+        |               |
+        +---------------+    +----------------+---------------+
+        |               |....|    |kernel|    |               |
+        +---------------+    +----------------+---------------+
+        |                         |
+        |----->   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


  parent reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-20  9:45 [PATCH v7 00/12] implement KASLR for powerpc/fsl_booke/32 Jason Yan
2019-09-20  9:45 ` [PATCH v7 01/12] powerpc: unify definition of M_IF_NEEDED Jason Yan
2019-09-20  9:45 ` [PATCH v7 02/12] powerpc: move memstart_addr and kernstart_addr to init-common.c Jason Yan
2019-09-20  9:45 ` [PATCH v7 03/12] powerpc: introduce kernstart_virt_addr to store the kernel base Jason Yan
2019-09-20  9:45 ` [PATCH v7 04/12] powerpc/fsl_booke/32: introduce create_kaslr_tlb_entry() helper Jason Yan
2019-09-20  9:45 ` [PATCH v7 05/12] powerpc/fsl_booke/32: introduce reloc_kernel_entry() helper Jason Yan
2019-09-20  9:45 ` [PATCH v7 06/12] powerpc/fsl_booke/32: implement KASLR infrastructure Jason Yan
2019-09-20  9:45 ` [PATCH v7 07/12] powerpc/fsl_booke/32: randomize the kernel image offset Jason Yan
2019-09-20  9:45 ` [PATCH v7 08/12] powerpc/fsl_booke/kaslr: clear the original kernel if randomized Jason Yan
2019-09-20  9:45 ` [PATCH v7 09/12] powerpc/fsl_booke/kaslr: support nokaslr cmdline parameter Jason Yan
2019-09-20  9:45 ` [PATCH v7 10/12] powerpc/fsl_booke/kaslr: dump out kernel offset information on panic Jason Yan
2019-09-20  9:45 ` [PATCH v7 11/12] powerpc/fsl_booke/kaslr: export offset in VMCOREINFO ELF notes Jason Yan
2019-09-20  9:45 ` Jason Yan [this message]
2019-09-24  5:52 ` [PATCH v7 00/12] implement KASLR for powerpc/fsl_booke/32 Jason Yan
2019-10-09  6:10   ` Jason Yan
2019-10-09  7:13     ` Scott Wood
2019-10-09  8:41       ` Jason Yan
2019-10-09 18:46         ` Scott Wood
2019-10-21  3:34           ` Jason Yan
2019-10-22 23:22             ` Scott Wood

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