Re: [PATCH v14 08/17] mm, arm64: untag user pointers in get_vaddr_frames

[Catalin Marinas <catalin.marinas-5wv7dgnIgG8@public.gmane.org>]

On Tue, Apr 30, 2019 at 03:25:04PM +0200, 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.
> 
> get_vaddr_frames uses provided user pointers for vma lookups, which can
> only by done with untagged pointers. Instead of locating and changing
> all callers of this function, perform untagging in it.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  mm/frame_vector.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/frame_vector.c b/mm/frame_vector.c
> index c64dca6e27c2..c431ca81dad5 100644
> --- a/mm/frame_vector.c
> +++ b/mm/frame_vector.c
> @@ -46,6 +46,8 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
>  	if (WARN_ON_ONCE(nr_frames > vec->nr_allocated))
>  		nr_frames = vec->nr_allocated;
>  
> +	start = untagged_addr(start);
> +
>  	down_read(&mm->mmap_sem);
>  	locked = 1;
>  	vma = find_vma_intersection(mm, start, start + 1);

Is this some buffer that the user may have malloc'ed? I got lost when
trying to track down the provenience of this buffer.

-- 
Catalin
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