The patch titled
Subject: mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd
has been added to the -mm mm-unstable branch. Its filename is
mm-memfd-add-write-seals-when-apply-seal_exec-to-executable-memfd.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memfd-add-write-seals-when-apply-seal_exec-to-executable-memfd.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Jeff Xu <jeffxu@xxxxxxxxxx>
Subject: mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd
Date: Thu, 15 Dec 2022 00:12:04 +0000
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.
Link: https://lkml.kernel.org/r/20221215001205.51969-5-jeffxu@xxxxxxxxxx
Signed-off-by: Jeff Xu <jeffxu@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Daniel Verkamp <dverkamp@xxxxxxxxxxxx>
Cc: David Herrmann <dh.herrmann@xxxxxxxxx>
Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Jorge Lucangeli Obes <jorgelo@xxxxxxxxxxxx>
Cc: kernel test robot <lkp@xxxxxxxxx>
Cc: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memfd.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/mm/memfd.c~mm-memfd-add-write-seals-when-apply-seal_exec-to-executable-memfd
+++ a/mm/memfd.c
@@ -222,6 +222,12 @@ static int memfd_add_seals(struct file *
}
}
+ /*
+ * SEAL_EXEC implys SEAL_WRITE, making W^X from the start.
+ */
+ if (seals & F_SEAL_EXEC && inode->i_mode & 0111)
+ seals |= F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE|F_SEAL_FUTURE_WRITE;
+
*file_seals |= seals;
error = 0;
_
Patches currently in -mm which might be from jeffxu@xxxxxxxxxx are
mm-memfd-add-mfd_noexec_seal-and-mfd_exec.patch
mm-memfd-add-write-seals-when-apply-seal_exec-to-executable-memfd.patch
selftests-memfd-add-tests-for-mfd_noexec_seal-mfd_exec.patch
