[RFC,v4,14/42] kmsan: make READ_ONCE_TASK_STACK() return initialized values

Commit Message

Alexander Potapenko Dec. 20, 2019, 6:49 p.m. UTC

To avoid false positives, assume that reading from the task stack
always produces initialized values.

Signed-off-by: Alexander Potapenko <[e-mail]>
To: Alexander Potapenko <[e-mail]>
Cc: Vegard Nossum <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Marco Elver <[e-mail]>
Cc: Andrey Konovalov <[e-mail]>
Cc: [e-mail]
Acked-by: Marco Elver <[e-mail]>

---
v4:
 - added an #include as requested by Marco Elver

Change-Id: Ie73e5a41fdc8195699928e65f5cbe0d3d3c9e2fa
---
 arch/x86/include/asm/unwind.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Patch

diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
index 499578f7e6d7..82c3bceb9999 100644
--- a/arch/x86/include/asm/unwind.h
+++ b/arch/x86/include/asm/unwind.h
@@ -4,6 +4,7 @@ 
 
 #include <linux/sched.h>
 #include <linux/ftrace.h>
+#include <linux/kmsan-checks.h>
 #include <asm/ptrace.h>
 #include <asm/stacktrace.h>
 
@@ -100,9 +101,10 @@  void unwind_module_init(struct module *mod, void *orc_ip, size_t orc_ip_size,
 #endif
 
 /*
- * This disables KASAN checking when reading a value from another task's stack,
- * since the other task could be running on another CPU and could have poisoned
- * the stack in the meantime.
+ * This disables KASAN/KMSAN checking when reading a value from another task's
+ * stack, since the other task could be running on another CPU and could have
+ * poisoned the stack in the meantime. Frame pointers are uninitialized by
+ * default, so for KMSAN we mark the return value initialized unconditionally.
  */
 #define READ_ONCE_TASK_STACK(task, x)			\
 ({							\
@@ -111,7 +113,7 @@  void unwind_module_init(struct module *mod, void *orc_ip, size_t orc_ip_size,
 		val = READ_ONCE(x);			\
 	else						\
 		val = READ_ONCE_NOCHECK(x);		\
-	val;						\
+	KMSAN_INIT_VALUE(val);				\
 })
 
 static inline bool task_on_another_cpu(struct task_struct *task)