[PATCH 1/2] bitmap: add sanity check function for find_bit()

[Yury Norov]

find_bit() requires a pointer aligned to it's size. However some
subsystems (fs, for example) cast char* variables to unsigned long*
before passing them to find_bit(). Many architectures allow unaligned
pointers with the cost of performance degradation.

This patch adds runtime check for the pointers to be aligned.

Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
---
 include/linux/find.h | 35 +++++++++++++++++++++++++++++++++++
 lib/Kconfig.debug    |  7 +++++++
 2 files changed, 42 insertions(+)

diff --git a/include/linux/find.h b/include/linux/find.h
index ccaf61a0f5fd..2d8f5419d787 100644
--- a/include/linux/find.h
+++ b/include/linux/find.h
@@ -7,6 +7,7 @@
 #endif
 
 #include <linux/bitops.h>
+#include <linux/bug.h>
 
 unsigned long _find_next_bit(const unsigned long *addr1, unsigned long nbits,
 				unsigned long start);
@@ -35,6 +36,14 @@ unsigned long _find_next_bit_le(const unsigned long *addr, unsigned
 				long size, unsigned long offset);
 #endif
 
+static __always_inline
+void check_find_bit(const unsigned long *addr)
+{
+#ifdef CONFIG_DEBUG_BITMAP
+	WARN_ON_ONCE(!IS_ALIGNED((unsigned long)addr, sizeof(unsigned long)));
+#endif
+}
+
 #ifndef find_next_bit
 /**
  * find_next_bit - find the next set bit in a memory region
@@ -49,6 +58,8 @@ static inline
 unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
 			    unsigned long offset)
 {
+	check_find_bit(addr);
+
 	if (small_const_nbits(size)) {
 		unsigned long val;
 
@@ -79,6 +90,9 @@ unsigned long find_next_and_bit(const unsigned long *addr1,
 		const unsigned long *addr2, unsigned long size,
 		unsigned long offset)
 {
+	check_find_bit(addr1);
+	check_find_bit(addr2);
+
 	if (small_const_nbits(size)) {
 		unsigned long val;
 
@@ -138,6 +152,8 @@ static inline
 unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
 				 unsigned long offset)
 {
+	check_find_bit(addr);
+
 	if (small_const_nbits(size)) {
 		unsigned long val;
 
@@ -164,6 +180,8 @@ unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
 static inline
 unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
 {
+	check_find_bit(addr);
+
 	if (small_const_nbits(size)) {
 		unsigned long val = *addr & GENMASK(size - 1, 0);
 
@@ -270,6 +288,9 @@ unsigned long find_first_and_bit(const unsigned long *addr1,
 				 const unsigned long *addr2,
 				 unsigned long size)
 {
+	check_find_bit(addr1);
+	check_find_bit(addr2);
+
 	if (small_const_nbits(size)) {
 		unsigned long val = *addr1 & *addr2 & GENMASK(size - 1, 0);
 
@@ -292,6 +313,8 @@ unsigned long find_first_and_bit(const unsigned long *addr1,
 static inline
 unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
 {
+	check_find_bit(addr);
+
 	if (small_const_nbits(size)) {
 		unsigned long val = *addr | ~GENMASK(size - 1, 0);
 
@@ -313,6 +336,8 @@ unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
 static inline
 unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
 {
+	check_find_bit(addr);
+
 	if (small_const_nbits(size)) {
 		unsigned long val = *addr & GENMASK(size - 1, 0);
 
@@ -417,18 +442,24 @@ extern unsigned long find_next_clump8(unsigned long *clump,
 static inline unsigned long find_next_zero_bit_le(const void *addr,
 		unsigned long size, unsigned long offset)
 {
+	check_find_bit(addr);
+
 	return find_next_zero_bit(addr, size, offset);
 }
 
 static inline unsigned long find_next_bit_le(const void *addr,
 		unsigned long size, unsigned long offset)
 {
+	check_find_bit(addr);
+
 	return find_next_bit(addr, size, offset);
 }
 
 static inline unsigned long find_first_zero_bit_le(const void *addr,
 		unsigned long size)
 {
+	check_find_bit(addr);
+
 	return find_first_zero_bit(addr, size);
 }
 
@@ -439,6 +470,8 @@ static inline
 unsigned long find_next_zero_bit_le(const void *addr, unsigned
 		long size, unsigned long offset)
 {
+	check_find_bit(addr);
+
 	if (small_const_nbits(size)) {
 		unsigned long val = *(const unsigned long *)addr;
 
@@ -472,6 +505,8 @@ static inline
 unsigned long find_next_bit_le(const void *addr, unsigned
 		long size, unsigned long offset)
 {
+	check_find_bit(addr);
+
 	if (small_const_nbits(size)) {
 		unsigned long val = *(const unsigned long *)addr;
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 3fc7abffc7aa..1c7dcd33fc2a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -543,6 +543,13 @@ endmenu # "Compiler options"
 
 menu "Generic Kernel Debugging Instruments"
 
+config DEBUG_BITMAP
+       bool "Debug bitmaps"
+       help
+         Say Y here if you want to check bitmap functions parameters at
+         the runtime. Enable CONFIG_DEBUG_BITMAP only for debugging because
+         it may affect performance.
+
 config MAGIC_SYSRQ
 	bool "Magic SysRq key"
 	depends on !UML
-- 
2.34.1