linux-kernel - [tip:x86/boot] x86/mm: Add memory hotplug support for KASLR memory randomization

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Message-ID: <tip-90397a41779645d3abba5599f6bb538fdcab9339@git.kernel.org>
Date:	Fri, 8 Jul 2016 13:36:40 -0700
From:	tip-bot for Thomas Garnier <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
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Subject: [tip:x86/boot] x86/mm: Add memory hotplug support for KASLR memory
 randomization

Commit-ID:  90397a41779645d3abba5599f6bb538fdcab9339
Gitweb:     http://git.kernel.org/tip/90397a41779645d3abba5599f6bb538fdcab9339
Author:     Thomas Garnier <thgarnie@...gle.com>
AuthorDate: Tue, 21 Jun 2016 17:47:06 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 8 Jul 2016 17:35:21 +0200

x86/mm: Add memory hotplug support for KASLR memory randomization

Add a new option (CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING) to define
the padding used for the physical memory mapping section when KASLR
memory is enabled. It ensures there is enough virtual address space when
CONFIG_MEMORY_HOTPLUG is used. The default value is 10 terabytes. If
CONFIG_MEMORY_HOTPLUG is not used, no space is reserved increasing the
entropy available.

Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Cc: Alexander Kuleshov <kuleshovmail@...il.com>
Cc: Alexander Popov <alpopov@...ecurity.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Cc: Baoquan He <bhe@...hat.com>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Borislav Petkov <bp@...e.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Christian Borntraeger <borntraeger@...ibm.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Dave Young <dyoung@...hat.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Jan Beulich <JBeulich@...e.com>
Cc: Joerg Roedel <jroedel@...e.de>
Cc: Jonathan Corbet <corbet@....net>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Lv Zheng <lv.zheng@...el.com>
Cc: Mark Salter <msalter@...hat.com>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Matt Fleming <matt@...eblueprint.co.uk>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephen Smalley <sds@...ho.nsa.gov>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Toshi Kani <toshi.kani@....com>
Cc: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Cc: Yinghai Lu <yinghai@...nel.org>
Cc: kernel-hardening@...ts.openwall.com
Cc: linux-doc@...r.kernel.org
Link: http://lkml.kernel.org/r/1466556426-32664-10-git-send-email-keescook@chromium.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/Kconfig    | 15 +++++++++++++++
 arch/x86/mm/kaslr.c |  7 ++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9719b8e..703413f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2010,6 +2010,21 @@ config RANDOMIZE_MEMORY
 
 	   If unsure, say N.
 
+config RANDOMIZE_MEMORY_PHYSICAL_PADDING
+	hex "Physical memory mapping padding" if EXPERT
+	depends on RANDOMIZE_MEMORY
+	default "0xa" if MEMORY_HOTPLUG
+	default "0x0"
+	range 0x1 0x40 if MEMORY_HOTPLUG
+	range 0x0 0x40
+	---help---
+	   Define the padding in terabytes added to the existing physical
+	   memory size during kernel memory randomization. It is useful
+	   for memory hotplug support but reduces the entropy available for
+	   address randomization.
+
+	   If unsure, leave at the default value.
+
 config HOTPLUG_CPU
 	bool "Support for hot-pluggable CPUs"
 	depends on SMP
diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index c939cfe..26dccd6 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -92,8 +92,13 @@ void __init kernel_randomize_memory(void)
 	if (!kaslr_memory_enabled())
 		return;
 
+	/*
+	 * Update Physical memory mapping to available and
+	 * add padding if needed (especially for memory hotplug support).
+	 */
 	BUG_ON(kaslr_regions[0].base != &page_offset_base);
-	memory_tb = ((max_pfn << PAGE_SHIFT) >> TB_SHIFT);
+	memory_tb = ((max_pfn << PAGE_SHIFT) >> TB_SHIFT) +
+		CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
 
 	/* Adapt phyiscal memory region size based on available memory */
 	if (memory_tb < kaslr_regions[0].size_tb)