linux-kernel - Re: [PATCH 1/2] memfd: Fix COW issue on MAP_PRIVATE and F_SEAL_FUTURE

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Message-ID: <20191108063308.GB18778@infradead.org>
Date:   Thu, 7 Nov 2019 22:33:08 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org,
        Nicolas Geoffray <ngeoffray@...gle.com>,
        kernel-team@...roid.com, Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH 1/2] memfd: Fix COW issue on MAP_PRIVATE and
 F_SEAL_FUTURE_WRITE mappings

> -		 * Since the F_SEAL_FUTURE_WRITE seals allow for a MAP_SHARED
> -		 * read-only mapping, take care to not allow mprotect to revert
> -		 * protections.
> +		 * Since an F_SEAL_FUTURE_WRITE sealed memfd can be mapped as
> +		 * MAP_SHARED and read-only, take care to not allow mprotect to
> +		 * revert protections on such mappings. Do this only for shared
> +		 * mappings. For private mappings, don't need to mask VM_MAYWRITE

This adds an > 80 char line.