linux-kernel - [PATCH -v1.1] x86/boot: Simplify pointer casting in choose_random

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Message-ID: <20160506115015.GI24044@pd.tnic>
Date:	Fri, 6 May 2016 13:50:15 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Kees Cook <keescook@...omium.org>, torvalds@...ux-foundation.org,
	hpa@...or.com, dyoung@...hat.com, tglx@...utronix.de,
	luto@...nel.org, peterz@...radead.org, dvlasenk@...hat.com,
	linux-kernel@...r.kernel.org, brgerst@...il.com,
	luto@...capital.net, akpm@...ux-foundation.org, bhe@...hat.com,
	yinghai@...nel.org, vgoyal@...hat.com,
	linux-tip-commits@...r.kernel.org
Subject: [PATCH -v1.1] x86/boot: Simplify pointer casting in
 choose_random_location()

From: Borislav Petkov <bp@...e.de>

Pass them down as unsigned long directly and get rid of more casting and
assignments.

Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Kees Cook <keescook@...omium.org>
---
 arch/x86/boot/compressed/kaslr.c | 17 ++++++-----------
 arch/x86/boot/compressed/misc.c  |  3 ++-
 arch/x86/boot/compressed/misc.h  | 10 +++++-----
 3 files changed, 13 insertions(+), 17 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 6392f0041b8a..a49f48317dad 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -350,20 +350,15 @@ static unsigned long find_random_addr(unsigned long minimum,
 	return slots_fetch_random();
 }
 
-unsigned char *choose_random_location(unsigned char *input_ptr,
+/*
+ * Since this function examines addresses much more numerically,
+ * it takes the input and output pointers as unsigned long.
+ */
+unsigned char *choose_random_location(unsigned long input,
 				      unsigned long input_size,
-				      unsigned char *output_ptr,
+				      unsigned long output,
 				      unsigned long output_size)
 {
-	/*
-	 * The caller of choose_random_location() uses unsigned char * for
-	 * buffer pointers since it performs decompression, elf parsing, etc.
-	 * Since this code examines addresses much more numerically,
-	 * unsigned long is used internally here. Instead of sprinkling
-	 * more casts into extract_kernel, do them here and at return.
-	 */
-	unsigned long input = (unsigned long)input_ptr;
-	unsigned long output = (unsigned long)output_ptr;
 	unsigned long choice = output;
 	unsigned long random_addr;
 
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 9536d778149e..f14db4e21654 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -366,7 +366,8 @@ 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_random_location(input_data, input_len, output,
+	output = choose_random_location((unsigned long)input_data, input_len,
+					(unsigned long)output,
 					max(output_len, kernel_total_size));
 
 	/* Validate memory location choices. */
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 1f23d022d241..0112005a3f23 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -67,20 +67,20 @@ int cmdline_find_option_bool(const char *option);
 
 #if CONFIG_RANDOMIZE_BASE
 /* kaslr.c */
-unsigned char *choose_random_location(unsigned char *input_ptr,
+unsigned char *choose_random_location(unsigned long input_ptr,
 				      unsigned long input_size,
-				      unsigned char *output_ptr,
+				      unsigned long output_ptr,
 				      unsigned long output_size);
 /* cpuflags.c */
 bool has_cpuflag(int flag);
 #else
 static inline
-unsigned char *choose_random_location(unsigned char *input_ptr,
+unsigned char *choose_random_location(unsigned long input_ptr,
 				      unsigned long input_size,
-				      unsigned char *output_ptr,
+				      unsigned long output_ptr,
 				      unsigned long output_size)
 {
-	return output_ptr;
+	return (unsigned char *)output_ptr;
 }
 #endif
 
-- 
2.7.3

-- 
Regards/Gruss,
    Boris.

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