linux-kernel - [PATCH v7 9/9] x86/mm: Memory hotplug support for KASLR memory randomization (x86

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Message-Id: <1466556426-32664-10-git-send-email-keescook@chromium.org>
Date:	Tue, 21 Jun 2016 17:47:06 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Kees Cook <keescook@...omium.org>,
	Thomas Garnier <thgarnie@...gle.com>,
	Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
	Borislav Petkov <bp@...e.de>, Baoquan He <bhe@...hat.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Juergen Gross <jgross@...e.com>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Toshi Kani <toshi.kani@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	Alexander Popov <alpopov@...ecurity.com>,
	Dave Young <dyoung@...hat.com>, Joerg Roedel <jroedel@...e.de>,
	Lv Zheng <lv.zheng@...el.com>,
	Mark Salter <msalter@...hat.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Jan Beulich <JBeulich@...e.com>, linux-kernel@...r.kernel.org,
	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
	kernel-hardening@...ts.openwall.com
Subject: [PATCH v7 9/9] x86/mm: Memory hotplug support for KASLR memory randomization (x86_64)

From: Thomas Garnier <thgarnie@...gle.com>

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>
---
 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 adab3fef3bb4..214b3fadbc11 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 4f91dc273062..3e9875f7fdda 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -114,8 +114,13 @@ 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)
-- 
2.7.4