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Subject: Re: [PATCH v2 2/4] selftest/vm: verify remap destination address in
 mremap_test
To:     Sidhartha Kumar <sidhartha.kumar@oracle.com>, shuah@kernel.org,
        akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Shuah Khan <skhan@linuxfoundation.org>
References: <20220420215721.4868-1-sidhartha.kumar@oracle.com>
 <20220420215721.4868-2-sidhartha.kumar@oracle.com>
From:   Shuah Khan <skhan@linuxfoundation.org>
Message-ID: <76cd8347-a8d0-3b56-a202-17ba2a73503d@linuxfoundation.org>
Date:   Thu, 21 Apr 2022 13:31:56 -0600
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On 4/20/22 3:57 PM, Sidhartha Kumar wrote:
> Because mremap does not have a MAP_FIXED_NOREPLACE flag, it can destroy
> existing mappings. This causes a segfault when regions such as text are
> remapped and the permissions are changed.
> 
> Verify the requested mremap destination address does not overlap any
> existing mappings by using mmap's MAP_FIXED_NOREPLACE flag. Keep
> incrementing the destination address until a valid mapping is found or
> fail the current test once the max address is reached.
> 
> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> ---
> v2:
> -rename remap_region_valid() to is_remap_region_valid().
> -change return value of is_remap_region_valid() to bool.
> -take out overflow check from is_remap_region_valid() to
>   inside caller.
> -fail just the current test on overflow rather than existing
>   the program
> -fix alignment of mmap calls
> -change "can't" to "couldn't" in error message
> -increment mremap destination address by dest_alignment
>   rather than src_alignment
> 
Thank you.

Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>

Andrew, please let me know if you would like me to take this
through kselftest tree.