atomic: add alignment check to instrumented atomic operations

Add a Kconfig option for debug builds which logs a warning when an
instrumented atomic operation takes place that's misaligned.  Some
platforms don't trap for this.

[[email protected]: added __DISABLE_EXPORTS conditional and refactored as helper function]
Link: https://lkml.kernel.org/r/51ebf844e006ca0de408f5d3a831e7b39d7fc31c.1768281748.git.fthain@linux-m68k.org
Link: https://lore.kernel.org/lkml/[email protected]/
Link: https://lore.kernel.org/linux-next/[email protected]/
Signed-off-by: Finn Thain <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Suggested-by: Geert Uytterhoeven <[email protected]>
Cc: Sasha Levin <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Daniel Borkman <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Eduard Zingerman <[email protected]>
Cc: Gary Guo <[email protected]>
Cc: Guo Ren <[email protected]>
Cc: Hao Luo <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: John Paul Adrian Glaubitz <[email protected]>
Cc: Jonas Bonn <[email protected]>
Cc: KP Singh <[email protected]>
Cc: Marc Rutland <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Stafford Horne <[email protected]>
Cc: Stanislav Fomichev <[email protected]>
Cc: Stefan Kristiansson <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: Yoshinori Sato <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Peter Zijlstra

include/linux/instrumented.h

@@ -7,6 +7,7 @@
 #ifndef _LINUX_INSTRUMENTED_H
 #define _LINUX_INSTRUMENTED_H
 
+#include <linux/bug.h>
 #include <linux/compiler.h>
 #include <linux/kasan-checks.h>
 #include <linux/kcsan-checks.h>
@@ -55,6 +56,13 @@ static __always_inline void instrument_read_write(const volatile void *v, size_t
 	kcsan_check_read_write(v, size);
 }
 
+static __always_inline void instrument_atomic_check_alignment(const volatile void *v, size_t size)
+{
+#ifndef __DISABLE_EXPORTS
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_DEBUG_ATOMIC) && ((unsigned long)v & (size - 1)));
+#endif
+}
+
 /**
  * instrument_atomic_read - instrument atomic read access
  * @v: address of access
@@ -67,6 +75,7 @@ static __always_inline void instrument_atomic_read(const volatile void *v, size_
 {
 	kasan_check_read(v, size);
 	kcsan_check_atomic_read(v, size);
+	instrument_atomic_check_alignment(v, size);
 }
 
 /**
@@ -81,6 +90,7 @@ static __always_inline void instrument_atomic_write(const volatile void *v, size
 {
 	kasan_check_write(v, size);
 	kcsan_check_atomic_write(v, size);
+	instrument_atomic_check_alignment(v, size);
 }
 
 /**
@@ -95,6 +105,7 @@ static __always_inline void instrument_atomic_read_write(const volatile void *v,
 {
 	kasan_check_write(v, size);
 	kcsan_check_atomic_read_write(v, size);
+	instrument_atomic_check_alignment(v, size);
 }
 
 /**

lib/Kconfig.debug

@@ -1360,6 +1360,16 @@ config DEBUG_PREEMPT
 	  depending on workload as it triggers debugging routines for each
 	  this_cpu operation. It should only be used for debugging purposes.
 
+config DEBUG_ATOMIC
+	bool "Debug atomic variables"
+	depends on DEBUG_KERNEL
+	help
+	  If you say Y here then the kernel will add a runtime alignment check
+	  to atomic accesses. Useful for architectures that do not have trap on
+	  mis-aligned access.
+
+	  This option has potentially significant overhead.
+
 menu "Lock Debugging (spinlocks, mutexes, etc...)"
 
 config LOCK_DEBUGGING_SUPPORT