linux-kernel - Re: [PATCH v16 09/16] fs, arm64: untag user pointers in fs/userfaultfd.c

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Message-ID: <201906072102.B58E6A609C@keescook>
Date:   Fri, 7 Jun 2019 21:03:43 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        linux-media@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Christian Koenig <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Khalid Aziz <khalid.aziz@...cle.com>, enh <enh@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christoph Hellwig <hch@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v16 09/16] fs, arm64: untag user pointers in
 fs/userfaultfd.c

On Mon, Jun 03, 2019 at 06:55:11PM +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.
> 
> userfaultfd code use provided user pointers for vma lookups, which can
> only by done with untagged pointers.
> 
> Untag user pointers in validate_range().
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>

"userfaultfd: untag user pointers"

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

-Kees

> ---
>  fs/userfaultfd.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 3b30301c90ec..24d68c3b5ee2 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -1263,21 +1263,23 @@ static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
>  }
>  
>  static __always_inline int validate_range(struct mm_struct *mm,
> -					  __u64 start, __u64 len)
> +					  __u64 *start, __u64 len)
>  {
>  	__u64 task_size = mm->task_size;
>  
> -	if (start & ~PAGE_MASK)
> +	*start = untagged_addr(*start);
> +
> +	if (*start & ~PAGE_MASK)
>  		return -EINVAL;
>  	if (len & ~PAGE_MASK)
>  		return -EINVAL;
>  	if (!len)
>  		return -EINVAL;
> -	if (start < mmap_min_addr)
> +	if (*start < mmap_min_addr)
>  		return -EINVAL;
> -	if (start >= task_size)
> +	if (*start >= task_size)
>  		return -EINVAL;
> -	if (len > task_size - start)
> +	if (len > task_size - *start)
>  		return -EINVAL;
>  	return 0;
>  }
> @@ -1327,7 +1329,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
>  		goto out;
>  	}
>  
> -	ret = validate_range(mm, uffdio_register.range.start,
> +	ret = validate_range(mm, &uffdio_register.range.start,
>  			     uffdio_register.range.len);
>  	if (ret)
>  		goto out;
> @@ -1516,7 +1518,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
>  	if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
>  		goto out;
>  
> -	ret = validate_range(mm, uffdio_unregister.start,
> +	ret = validate_range(mm, &uffdio_unregister.start,
>  			     uffdio_unregister.len);
>  	if (ret)
>  		goto out;
> @@ -1667,7 +1669,7 @@ static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
>  	if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
>  		goto out;
>  
> -	ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
> +	ret = validate_range(ctx->mm, &uffdio_wake.start, uffdio_wake.len);
>  	if (ret)
>  		goto out;
>  
> @@ -1707,7 +1709,7 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
>  			   sizeof(uffdio_copy)-sizeof(__s64)))
>  		goto out;
>  
> -	ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
> +	ret = validate_range(ctx->mm, &uffdio_copy.dst, uffdio_copy.len);
>  	if (ret)
>  		goto out;
>  	/*
> @@ -1763,7 +1765,7 @@ static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
>  			   sizeof(uffdio_zeropage)-sizeof(__s64)))
>  		goto out;
>  
> -	ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
> +	ret = validate_range(ctx->mm, &uffdio_zeropage.range.start,
>  			     uffdio_zeropage.range.len);
>  	if (ret)
>  		goto out;
> -- 
> 2.22.0.rc1.311.g5d7573a151-goog
> 

-- 
Kees Cook