Re: [PATCH v13 13/20] bpf, arm64: untag user pointers in stack_map_get_build_id_offset

Andrey Konovalov
2019-04-01T16:00:22Z

On Fri, Mar 22, 2019 at 4:52 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Wed, Mar 20, 2019 at 03:51:27PM +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.
> >
> > stack_map_get_build_id_offset() uses provided user pointers for vma
> > lookups, which can only by done with untagged pointers.
> >
> > Untag user pointers in this function for doing the lookup and
> > calculating the offset, but save as is in the bpf_stack_build_id
> > struct.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> > ---
> > kernel/bpf/stackmap.c | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
> > index 950ab2f28922..bb89341d3faf 100644
> > --- a/kernel/bpf/stackmap.c
> > +++ b/kernel/bpf/stackmap.c
> > @@ -320,7 +320,9 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
> > }
> >
> > for (i = 0; i < trace_nr; i++) {
> > - vma = find_vma(current->mm, ips[i]);
> > + u64 untagged_ip = untagged_addr(ips[i]);
> > +
> > + vma = find_vma(current->mm, untagged_ip);
> > if (!vma || stack_map_get_build_id(vma, id_offs[i].build_id)) {
> > /* per entry fall back to ips */
> > id_offs[i].status = BPF_STACK_BUILD_ID_IP;
> > @@ -328,7 +330,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
> > memset(id_offs[i].build_id, 0, BPF_BUILD_ID_SIZE);
> > continue;
> > }
> > - id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ips[i]
> > + id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + untagged_ip
> > - vma->vm_start;
> > id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
> > }
>
> Can the ips[*] here ever be tagged?

Those are instruction pointers AFAIU, so no, not within the current
ABI. I'll drop this patch. Thanks!

>
> --
> Catalin