[PATCH v13 11/20] tracing, arm64: untag user pointers in seq_print_user_ip

[Andrey Konovalov]

On Fri, Mar 22, 2019 at 4:45 PM Catalin Marinas <catalin.marinas at arm.com> wrote:
>
> On Wed, Mar 20, 2019 at 03:51:25PM +0100, Andrey Konovalov wrote:
> > This patch is a part of a series that extends arm64 kernel ABI to allow to
> > pass tagged user pointers (with the top byte set to something else other
> > than 0x00) as syscall arguments.
> >
> > seq_print_user_ip() uses provided user pointers for vma lookups, which
> > can only by done with untagged pointers.
> >
> > Untag user pointers in this function.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
> > ---
> >  kernel/trace/trace_output.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> > index 54373d93e251..6376bee93c84 100644
> > --- a/kernel/trace/trace_output.c
> > +++ b/kernel/trace/trace_output.c
> > @@ -370,6 +370,7 @@ static int seq_print_user_ip(struct trace_seq *s, struct mm_struct *mm,
> >  {
> >       struct file *file = NULL;
> >       unsigned long vmstart = 0;
> > +     unsigned long untagged_ip = untagged_addr(ip);
> >       int ret = 1;
> >
> >       if (s->full)
> > @@ -379,7 +380,7 @@ static int seq_print_user_ip(struct trace_seq *s, struct mm_struct *mm,
> >               const struct vm_area_struct *vma;
> >
> >               down_read(&mm->mmap_sem);
> > -             vma = find_vma(mm, ip);
> > +             vma = find_vma(mm, untagged_ip);
> >               if (vma) {
> >                       file = vma->vm_file;
> >                       vmstart = vma->vm_start;
> > @@ -388,7 +389,7 @@ static int seq_print_user_ip(struct trace_seq *s, struct mm_struct *mm,
> >                       ret = trace_seq_path(s, &file->f_path);
> >                       if (ret)
> >                               trace_seq_printf(s, "[+0x%lx]",
> > -                                              ip - vmstart);
> > +                                              untagged_ip - vmstart);
> >               }
> >               up_read(&mm->mmap_sem);
> >       }
>
> How would we end up with a tagged address here? Does "ip" here imply
> instruction pointer, which we wouldn't tag?

Yes, it's the instruction pointer. I think I got confused and decided
that it's OK to have instruction pointer tagged, but I guess it's not
a part of this ABI relaxation. I'll drop the patches that untag
instruction pointers.