On Wed, Mar 25, 2020 at 5:13 PM <glider@xxxxxxxxxx> wrote:
>
> To avoid false positives, assume that reading from the task stack
> always produces initialized values.
>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> To: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Acked-by: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
>
> ---
> 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(-)
>
> diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
> index 499578f7e6d7b..82c3bceb9999c 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)
> --
> 2.25.1.696.g5e7596f4ac-goog
>
