linux-kernel - [PATCH v7 3/4] atomic: Add alignment check to instrumented atomic operations

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <51ebf844e006ca0de408f5d3a831e7b39d7fc31c.1768281748.git.fthain@linux-m68k.org>
Date: Tue, 13 Jan 2026 16:22:28 +1100
From: Finn Thain <fthain@...ux-m68k.org>
To: Andrew Morton <akpm@...ux-foundation.org>,
    Peter Zijlstra <peterz@...radead.org>,
    Will Deacon <will@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>,
    Boqun Feng <boqun.feng@...il.com>,
    Gary Guo <gary@...yguo.net>,
    Mark Rutland <mark.rutland@....com>,
    linux-arch@...r.kernel.org,
    linux-kernel@...r.kernel.org,
    linux-m68k@...ts.linux-m68k.org,
    Sasha Levin <sashal@...nel.org>,
    Thomas Gleixner <tglx@...utronix.de>,
    Ingo Molnar <mingo@...hat.com>,
    Borislav Petkov <bp@...en8.de>,
    Dave Hansen <dave.hansen@...ux.intel.com>,
    Ard Biesheuvel <ardb@...nel.org>,
    "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH v7 3/4] atomic: Add alignment check to instrumented atomic
 operations

From: Peter Zijlstra <peterz@...radead.org>

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.

[ fthain: added __DISABLE_EXPORTS conditional and refactored as helper
function. ]

Cc: Sasha Levin <sashal@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: "H. Peter Anvin" <hpa@...or.com>
Link: https://lore.kernel.org/lkml/20250901093600.GF4067720@noisy.programming.kicks-ass.net/
Link: https://lore.kernel.org/linux-next/df9fbd22-a648-ada4-fee0-68fe4325ff82@linux-m68k.org/
Signed-off-by: Finn Thain <fthain@...ux-m68k.org>

---
Checkpatch.pl says...
ERROR: Missing Signed-off-by: line by nominal patch author 'Peter Ziljstra <peterz@...radead.org>'

---
Changed since v6:
 - Implemented helper function earlier in patch series, as requested by Ard.
 - Dropped __DISABLE_BUG_TABLE macro in favour of __DISABLE_EXPORTS, as
 requested by Peter.

Changed since v5:
 - Add new __DISABLE_BUG_TABLE macro to prevent a build failure on those
architectures which use atomics in pre-boot code like the EFI stub loader:

x86_64-linux-gnu-ld: error: unplaced orphan section `__bug_table' from `arch/x86/boot/compressed/sev-handle-vc.o'

Changed since v2:
 - Always check for natural alignment.
---
 include/linux/instrumented.h | 11 +++++++++++
 lib/Kconfig.debug            | 10 ++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/instrumented.h b/include/linux/instrumented.h
index 711a1f0d1a73..e34b6a557e0a 100644
--- a/include/linux/instrumented.h
+++ b/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);
 }
 
 /**
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ba36939fda79..4b4d1445ef9c 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1359,6 +1359,16 @@ 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
-- 
2.49.1