Re: [PATCH v6 4/6] mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd

On Wed, Dec 07, 2022 at 03:49:37PM +0000, jeffxu@chromium.org wrote:

From: Jeff Xu jeffxu@google.com

In order to avoid WX mappings, add F_SEAL_WRITE when apply F_SEAL_EXEC to an executable memfd, so W^X from start.

This implys application need to fill the content of the memfd first, after F_SEAL_EXEC is applied, application can no longer modify the content of the memfd.

Typically, application seals the memfd right after writing to it. For example:

1. memfd_create(MFD_EXEC).
2. write() code to the memfd.
3. fcntl(F_ADD_SEALS, F_SEAL_EXEC) to convert the memfd to W^X.
4. call exec() on the memfd.

Signed-off-by: Jeff Xu jeffxu@google.com

Reviewed-by: Kees Cook keescook@chromium.org