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

Andrey Konovalov
2019-04-01T15:38:40Z

On Fri, Mar 22, 2019 at 4:45 PM Catalin Marinas <catalin.marinas@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@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.