[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20221206152358.1966099-5-jeffxu@google.com>
Date: Tue, 6 Dec 2022 15:23:56 +0000
From: jeffxu@...omium.org
To: skhan@...uxfoundation.org, keescook@...omium.org
Cc: akpm@...ux-foundation.org, dmitry.torokhov@...il.com,
dverkamp@...omium.org, hughd@...gle.com, jeffxu@...gle.com,
jorgelo@...omium.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
jannh@...gle.com, linux-hardening@...r.kernel.org,
Jeff Xu <jeffxu@...omium.org>
Subject: [PATCH v5 4/6] mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd
From: Jeff Xu <jeffxu@...omium.org>
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@...omium.org>
---
mm/memfd.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/mm/memfd.c b/mm/memfd.c
index ec70675a7069..92f0a5765f7c 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -222,6 +222,12 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
}
}
+ /*
+ * 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;
--
2.39.0.rc0.267.gcb52ba06e7-goog
Powered by blists - more mailing lists