Re: [PATCH v16 15/16] vfio/type1, arm64: untag user pointers in vaddr_get_pfn

From: Kees Cook <keescook@chromium.org>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org,
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	Catalin Marinas <catalin.marinas@arm.com>,
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	Mark Rutland <mark.rutland@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Yishai Hadas <yishaih@mellanox.com>,
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	Khalid Aziz <khalid.aziz@oracle.com>, enh <enh@google.com>,
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	Lee Smith <Lee.Smith@arm.com>,
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	Robin Murphy <robin.murphy@arm.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	Szabolcs Nagy <Szabolcs.Nagy@arm.com>
Subject: Re: [PATCH v16 15/16] vfio/type1, arm64: untag user pointers in vaddr_get_pfn
Date: Fri, 7 Jun 2019 20:58:05 -0700	[thread overview]
Message-ID: <201906072058.BB57EFA@keescook> (raw)
In-Reply-To: <c529e1eeea7700beff197c4456da6a882ce2efb7.1559580831.git.andreyknvl@google.com>

On Mon, Jun 03, 2019 at 06:55:17PM +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.
> 
> vaddr_get_pfn() 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>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  drivers/vfio/vfio_iommu_type1.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 3ddc375e7063..528e39a1c2dd 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -384,6 +384,8 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
>  
>  	down_read(&mm->mmap_sem);
>  
> +	vaddr = untagged_addr(vaddr);
> +
>  	vma = find_vma_intersection(mm, vaddr, vaddr + 1);
>  
>  	if (vma && vma->vm_flags & VM_PFNMAP) {
> -- 
> 2.22.0.rc1.311.g5d7573a151-goog
> 

-- 
Kees Cook