On Wed, 1 Sept 2021 at 16:06, Vasily Gorbik <gor@xxxxxxxxxxxxx> wrote:
> current_stack_pointer() simply returns current value of %r15. If
> current_stack_pointer() caller allocates stack (which is the case in
> unwind code) %r15 points to a stack frame allocated for callees, meaning
> current_stack_pointer() caller (e.g. stack_trace_save) will end up in
> the stacktrace. This is not expected by stack_trace_save*() callers and
> causes problems.
>
> current_frame_address() on the other hand returns function stack frame
> address, which matches %r15 upon function invocation. Using it in
> get_stack_pointer() makes it more aligned with x86 implementation
> (according to BACKTRACE_SELF_TEST output) and meets stack_trace_save*()
> caller's expectations, notably KCSAN.
>
> Also make sure unwind_start is always inlined.
>
> Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Suggested-by: Marco Elver <elver@xxxxxxxxxx>
> Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Tested-by: Marco Elver <elver@xxxxxxxxxx>
Thanks!
> ---
> arch/s390/include/asm/stacktrace.h | 20 ++++++++++----------
> arch/s390/include/asm/unwind.h | 8 ++++----
> 2 files changed, 14 insertions(+), 14 deletions(-)
>
> diff --git a/arch/s390/include/asm/stacktrace.h b/arch/s390/include/asm/stacktrace.h
> index 3d8a4b94c620..22c41d7fd95c 100644
> --- a/arch/s390/include/asm/stacktrace.h
> +++ b/arch/s390/include/asm/stacktrace.h
> @@ -34,16 +34,6 @@ static inline bool on_stack(struct stack_info *info,
> return addr >= info->begin && addr + len <= info->end;
> }
>
> -static __always_inline unsigned long get_stack_pointer(struct task_struct *task,
> - struct pt_regs *regs)
> -{
> - if (regs)
> - return (unsigned long) kernel_stack_pointer(regs);
> - if (task == current)
> - return current_stack_pointer();
> - return (unsigned long) task->thread.ksp;
> -}
> -
> /*
> * Stack layout of a C stack frame.
> */
> @@ -74,6 +64,16 @@ struct stack_frame {
> ((unsigned long)__builtin_frame_address(0) - \
> offsetof(struct stack_frame, back_chain))
>
> +static __always_inline unsigned long get_stack_pointer(struct task_struct *task,
> + struct pt_regs *regs)
> +{
> + if (regs)
> + return (unsigned long) kernel_stack_pointer(regs);
> + if (task == current)
> + return current_frame_address();
> + return (unsigned long) task->thread.ksp;
> +}
> +
> /*
> * To keep this simple mark register 2-6 as being changed (volatile)
> * by the called function, even though register 6 is saved/nonvolatile.
> diff --git a/arch/s390/include/asm/unwind.h b/arch/s390/include/asm/unwind.h
> index de9006b0cfeb..5ebf534ef753 100644
> --- a/arch/s390/include/asm/unwind.h
> +++ b/arch/s390/include/asm/unwind.h
> @@ -55,10 +55,10 @@ static inline bool unwind_error(struct unwind_state *state)
> return state->error;
> }
>
> -static inline void unwind_start(struct unwind_state *state,
> - struct task_struct *task,
> - struct pt_regs *regs,
> - unsigned long first_frame)
> +static __always_inline void unwind_start(struct unwind_state *state,
> + struct task_struct *task,
> + struct pt_regs *regs,
> + unsigned long first_frame)
> {
> task = task ?: current;
> first_frame = first_frame ?: get_stack_pointer(task, regs);
> --
> 2.25.4
