[PATCH 1/9] drivers/char/random: Eliminate randomize_range().

[George Spelvin]

This is only called in three places, each of which is trivially
replaced by a call to get_random_int() followed by a bit mask.
(It's to randomize the start of the brk() range by 0..32M bytes,
0..8K pages, which is 13 bits of entropy.)

There is a slight behaviour change, as randomize_range() used PAGE_ALIGN()
which rounds up, but it appears that rounding down was the intention.
---
 arch/arm/kernel/process.c    |    3 +--
 arch/x86/kernel/process.c    |    3 +--
 arch/x86/kernel/sys_x86_64.c |    7 ++-----
 drivers/char/random.c        |   19 -------------------
 include/linux/random.h       |    1 -
 5 files changed, 4 insertions(+), 29 deletions(-)

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 94bbedb..ffb7c87 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -479,8 +479,7 @@ unsigned long get_wchan(struct task_struct *p)
 
 unsigned long arch_randomize_brk(struct mm_struct *mm)
 {
-	unsigned long range_end = mm->brk + 0x02000000;
-	return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
+	return mm->brk + (get_random_int() & 0x01ffffff & PAGE_MASK);
 }
 
 #ifdef CONFIG_MMU
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ff45541..dcec1a1 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -677,7 +677,6 @@ unsigned long arch_align_stack(unsigned long sp)
 
 unsigned long arch_randomize_brk(struct mm_struct *mm)
 {
-	unsigned long range_end = mm->brk + 0x02000000;
-	return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
+	return mm->brk + (get_random_int() & 0x01ffffff & PAGE_MASK);
 }
 
diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index ff14a50..0f874f7 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -46,11 +46,8 @@ static void find_start_end(unsigned long flags, unsigned long *begin,
 		   of playground for now. -AK */
 		*begin = 0x40000000;
 		*end = 0x80000000;
-		if (current->flags & PF_RANDOMIZE) {
-			new_begin = randomize_range(*begin, *begin + 0x02000000, 0);
-			if (new_begin)
-				*begin = new_begin;
-		}
+		if (current->flags & PF_RANDOMIZE)
+			*begin += (get_random_int() & 0x01ffffff & PAGE_MASK);
 	} else {
 		*begin = TASK_UNMAPPED_BASE;
 		*end = TASK_SIZE;
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 72a4fcb..cea9ddc 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1639,22 +1639,3 @@ unsigned int get_random_int(void)
 
 	return ret;
 }
-
-/*
- * randomize_range() returns a start address such that
- *
- *    [...... <range> .....]
- *  start                  end
- *
- * a <range> with size "len" starting at the return value is inside in the
- * area defined by [start, end], but is otherwise randomized.
- */
-unsigned long
-randomize_range(unsigned long start, unsigned long end, unsigned long len)
-{
-	unsigned long range = end - len - start;
-
-	if (end <= start + len)
-		return 0;
-	return PAGE_ALIGN(get_random_int() % range + start);
-}
diff --git a/include/linux/random.h b/include/linux/random.h
index fb7ab9d..0e17434 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -73,7 +73,6 @@ extern const struct file_operations random_fops, urandom_fops;
 #endif
 
 unsigned int get_random_int(void);
-unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len);
 
 u32 random32(void);
 void srandom32(u32 seed);
-- 
1.7.4.1

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