linux-kernel - [PATCH 5/6] x86, KASLR: Clarify purpose of kaslr.c

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Message-Id: <1460997735-24785-6-git-send-email-keescook@chromium.org>
Date:	Mon, 18 Apr 2016 09:42:14 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Kees Cook <keescook@...omium.org>, Yinghai Lu <yinghai@...nel.org>,
	Baoquan He <bhe@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	"H.J. Lu" <hjl.tools@...il.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH 5/6] x86, KASLR: Clarify purpose of kaslr.c

The name "choose_kernel_location" isn't specific enough, and doesn't
describe the primary thing it does: choosing a random location. This
patch renames it to "choose_random_location", and clarifies the what
routines are contained in the kaslr.c source file.

Suggested-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/boot/compressed/kaslr.c | 13 ++++++++++++-
 arch/x86/boot/compressed/misc.c  |  2 +-
 arch/x86/boot/compressed/misc.h  |  4 ++--
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index a51ec841c9b9..9e03190d00ad 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -1,3 +1,14 @@
+/*
+ * kaslr.c
+ *
+ * This contains the routines needed to generate a reasonable level of
+ * entropy to choose a randomized kernel base address offset in support
+ * of Kernel Address Space Layout Randomization (KASLR). Additionally
+ * handles walking the physical memory maps (and tracking memory regions
+ * to avoid) in order to select a physical memory location that can
+ * contain the entire properly aligned running kernel image.
+ *
+ */
 #include "misc.h"
 
 #include <asm/msr.h>
@@ -295,7 +306,7 @@ static unsigned long find_random_addr(unsigned long minimum,
 	return slots_fetch_random();
 }
 
-unsigned char *choose_kernel_location(unsigned char *input,
+unsigned char *choose_random_location(unsigned char *input,
 				      unsigned long input_size,
 				      unsigned char *output,
 				      unsigned long output_size)
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 0d69e809673a..ad8c01ac2885 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -431,7 +431,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 	 * the entire decompressed kernel plus relocation table, or the
 	 * entire decompressed kernel plus .bss and .brk sections.
 	 */
-	output = choose_kernel_location(input_data, input_len, output,
+	output = choose_random_location(input_data, input_len, output,
 					output_len > run_size ? output_len
 							      : run_size);
 
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 1f750a516580..9887e0d4aaeb 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -67,7 +67,7 @@ int cmdline_find_option_bool(const char *option);
 
 #if CONFIG_RANDOMIZE_BASE
 /* kaslr.c */
-unsigned char *choose_kernel_location(unsigned char *input,
+unsigned char *choose_random_location(unsigned char *input,
 				      unsigned long input_size,
 				      unsigned char *output,
 				      unsigned long output_size);
@@ -75,7 +75,7 @@ unsigned char *choose_kernel_location(unsigned char *input,
 bool has_cpuflag(int flag);
 #else
 static inline
-unsigned char *choose_kernel_location(unsigned char *input,
+unsigned char *choose_random_location(unsigned char *input,
 				      unsigned long input_size,
 				      unsigned char *output,
 				      unsigned long output_size)
-- 
2.6.3