Re: [PATCH v13 12/20] uprobes, arm64: untag user pointers in find_active_uprobe

Catalin Marinas
2019-03-22T15:46:58Z

On Wed, Mar 20, 2019 at 03:51:26PM +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.
>
> find_active_uprobe() uses user pointers (obtained via
> instruction_pointer(regs)) 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/events/uprobes.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index c5cde87329c7..d3a2716a813a 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1992,6 +1992,8 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
> struct uprobe *uprobe = NULL;
> struct vm_area_struct *vma;
>
> + bp_vaddr = untagged_addr(bp_vaddr);
> +
> down_read(&mm->mmap_sem);
> vma = find_vma(mm, bp_vaddr);
> if (vma && vma->vm_start <= bp_vaddr) {

Similarly here, that's a breakpoint address, hence instruction pointer
(PC) which is untagged.

--
Catalin