Message-ID: <4d29a9ec-027d-06b9-8543-87d386e58c94@redhat.com>
Date:   Thu, 16 Feb 2023 10:24:50 +0100
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Subject: Re: [PATCH v4 2/2] mm/userfaultfd: add VM_WARN_ONCE()
To:     Muhammad Usama Anjum <usama.anjum@collabora.com>,
        peterx@redhat.com, Andrew Morton <akpm@linux-foundation.org>
Cc:     kernel@collabora.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <20230216091656.2045471-1-usama.anjum@collabora.com>
 <20230216091656.2045471-2-usama.anjum@collabora.com>
Content-Language: en-US
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20230216091656.2045471-2-usama.anjum@collabora.com>
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On 16.02.23 10:16, Muhammad Usama Anjum wrote:
> Add VM_WARN_ONCE() to uffd_wp_range() to detect range (start, len) abuse.
> 
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
> ---
>   mm/userfaultfd.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 77c5839e591c..d89ed44d2668 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -717,6 +717,8 @@ long uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma,
>   	struct mmu_gather tlb;
>   	long ret;
>   
> +	VM_WARN_ONCE(start < dst_vma->vm_start || start + len > dst_vma->vm_end,
> +		     "The address range exceeds VMA boundary.\n");

VM_WARN_ON_ONCE is sufficient (sorry for spelling out the wrong variant 
earlier).

These kinds of bugs are expected to be found early during testing, still 
it might make sense to implement a backup path

if (WARN_ON_ONCE(...))
	return -EINVAL;

But we can't use VM_WARN_ON_ONCE here, so we can't compile it out 
anymore ... so I guess a simple VM_WARN_ON_ONCE() is sufficient.

-- 
Thanks,

David / dhildenb