The unwind code can read uninitialized frames. Furthermore, even in
the good case, KMSAN does not emit shadow for backchains. Therefore
disable it for the unwinding functions.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 arch/s390/kernel/unwind_bc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/s390/kernel/unwind_bc.c b/arch/s390/kernel/unwind_bc.c
index 0ece156fdd7c..7ecaab24783f 100644
--- a/arch/s390/kernel/unwind_bc.c
+++ b/arch/s390/kernel/unwind_bc.c
@@ -49,6 +49,7 @@ static inline bool is_final_pt_regs(struct unwind_state *state,
 	       READ_ONCE_NOCHECK(regs->psw.mask) & PSW_MASK_PSTATE;
 }
 
+__no_kmsan_checks
 bool unwind_next_frame(struct unwind_state *state)
 {
 	struct stack_info *info = &state->stack_info;
@@ -118,6 +119,7 @@ bool unwind_next_frame(struct unwind_state *state)
 }
 EXPORT_SYMBOL_GPL(unwind_next_frame);
 
+__no_kmsan_checks
 void __unwind_start(struct unwind_state *state, struct task_struct *task,
 		    struct pt_regs *regs, unsigned long first_frame)
 {
-- 
2.41.0

On Wed, Nov 15, 2023 at 9:35 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote:
>
> The unwind code can read uninitialized frames. Furthermore, even in
> the good case, KMSAN does not emit shadow for backchains. Therefore
> disable it for the unwinding functions.
>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  arch/s390/kernel/unwind_bc.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/s390/kernel/unwind_bc.c b/arch/s390/kernel/unwind_bc.c
> index 0ece156fdd7c..7ecaab24783f 100644
> --- a/arch/s390/kernel/unwind_bc.c
> +++ b/arch/s390/kernel/unwind_bc.c
> @@ -49,6 +49,7 @@ static inline bool is_final_pt_regs(struct unwind_state *state,
>                READ_ONCE_NOCHECK(regs->psw.mask) & PSW_MASK_PSTATE;
>  }
>
> +__no_kmsan_checks

Please add some comments to the source file to back this annotation,
so that the intent is not lost in git history.

On Thu, Nov 16, 2023 at 10:04 AM Alexander Potapenko <glider@google.com> wrote:
>
> On Wed, Nov 15, 2023 at 9:35 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote:
> >
> > The unwind code can read uninitialized frames. Furthermore, even in
> > the good case, KMSAN does not emit shadow for backchains. Therefore
> > disable it for the unwinding functions.
> >
> > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> > ---
> >  arch/s390/kernel/unwind_bc.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/s390/kernel/unwind_bc.c b/arch/s390/kernel/unwind_bc.c
> > index 0ece156fdd7c..7ecaab24783f 100644
> > --- a/arch/s390/kernel/unwind_bc.c
> > +++ b/arch/s390/kernel/unwind_bc.c
> > @@ -49,6 +49,7 @@ static inline bool is_final_pt_regs(struct unwind_state *state,
> >                READ_ONCE_NOCHECK(regs->psw.mask) & PSW_MASK_PSTATE;
> >  }
> >
> > +__no_kmsan_checks
>
> Please add some comments to the source file to back this annotation,
> so that the intent is not lost in git history.

Apart from that,

Reviewed-by: Alexander Potapenko <glider@google.com>


-- 
Alexander Potapenko
Software Engineer

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