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* [PATCH -manpage 0/2]
@ 2019-03-14 21:48 Joel Fernandes (Google)
  2019-03-14 21:48 ` [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal Joel Fernandes (Google)
  2019-03-14 21:48 ` [PATCH -manpage 2/2] memfd_create.2: " Joel Fernandes (Google)
  0 siblings, 2 replies; 3+ messages in thread
From: Joel Fernandes (Google) @ 2019-03-14 21:48 UTC (permalink / raw)
  To: linux-kernel, mtk.manpages
  Cc: Joel Fernandes (Google),
	Andrew Morton, Andy Lutomirski, dancol, Jann Horn, John Stultz,
	kernel-team, linux-api, linux-man, linux-mm, Matthew Wilcox,
	Mike Kravetz, Shuah Khan, Stephen Rothwell

This documentation is for F_SEAL_FUTURE_WRITE patches that are in linux-next.

Joel Fernandes (Google) (2):
fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal
memfd_create.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal

man2/fcntl.2        | 15 +++++++++++++++
man2/memfd_create.2 | 15 ++++++++++++++-
2 files changed, 29 insertions(+), 1 deletion(-)

--
2.21.0.360.g471c308f928-goog

^ permalink raw reply	[flat|nested] 3+ messages in thread

* [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal
  2019-03-14 21:48 [PATCH -manpage 0/2] Joel Fernandes (Google)
@ 2019-03-14 21:48 ` Joel Fernandes (Google)
  2019-03-14 21:48 ` [PATCH -manpage 2/2] memfd_create.2: " Joel Fernandes (Google)
  1 sibling, 0 replies; 3+ messages in thread
From: Joel Fernandes (Google) @ 2019-03-14 21:48 UTC (permalink / raw)
  To: linux-kernel, mtk.manpages
  Cc: Joel Fernandes (Google),
	Andrew Morton, Andy Lutomirski, dancol, Jann Horn, John Stultz,
	kernel-team, linux-api, linux-man, linux-mm, Matthew Wilcox,
	Mike Kravetz, Shuah Khan, Stephen Rothwell

More details of the seal can be found in the LKML patch:
https://lore.kernel.org/lkml/20181120052137.74317-1-joel@joelfernandes.org/T/#t

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 man2/fcntl.2 | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/man2/fcntl.2 b/man2/fcntl.2
index fce4f4c2b3bd..e01e2c075b5b 100644
--- a/man2/fcntl.2
+++ b/man2/fcntl.2
@@ -1525,6 +1525,21 @@ Furthermore, if there are any asynchronous I/O operations
 .RB ( io_submit (2))
 pending on the file,
 all outstanding writes will be discarded.
+.TP
+.BR F_SEAL_FUTURE_WRITE
+If this seal is set, the contents of the file can be modified only from
+existing writeable mappings that were created prior to the seal being set.
+Any attempt to create a new writeable mapping on the memfd via
+.BR mmap (2)
+will fail with
+.BR EPERM.
+Also any attempts to write to the memfd via
+.BR write (2)
+will fail with
+.BR EPERM.
+This is useful in situations where existing writable mapped regions need to be
+kept intact while preventing any future writes. For example, to share a
+read-only memory buffer to other processes that only the sender can write to.
 .\"
 .SS File read/write hints
 Write lifetime hints can be used to inform the kernel about the relative
-- 
2.21.0.360.g471c308f928-goog

^ permalink raw reply	[flat|nested] 3+ messages in thread

* [PATCH -manpage 2/2] memfd_create.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal
  2019-03-14 21:48 [PATCH -manpage 0/2] Joel Fernandes (Google)
  2019-03-14 21:48 ` [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal Joel Fernandes (Google)
@ 2019-03-14 21:48 ` " Joel Fernandes (Google)
  1 sibling, 0 replies; 3+ messages in thread
From: Joel Fernandes (Google) @ 2019-03-14 21:48 UTC (permalink / raw)
  To: linux-kernel, mtk.manpages
  Cc: Joel Fernandes (Google),
	Andrew Morton, Andy Lutomirski, dancol, Jann Horn, John Stultz,
	kernel-team, linux-api, linux-man, linux-mm, Matthew Wilcox,
	Mike Kravetz, Shuah Khan, Stephen Rothwell

More details of the seal can be found in the LKML patch:
https://lore.kernel.org/lkml/20181120052137.74317-1-joel@joelfernandes.org/T/#t

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 man2/memfd_create.2 | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/man2/memfd_create.2 b/man2/memfd_create.2
index 15b1362f5525..3b7f032407ed 100644
--- a/man2/memfd_create.2
+++ b/man2/memfd_create.2
@@ -280,7 +280,15 @@ in order to restrict further modifications on the file.
 (If placing the seal
 .BR F_SEAL_WRITE ,
 then it will be necessary to first unmap the shared writable mapping
-created in the previous step.)
+created in the previous step. Otherwise, behavior similar to
+.BR F_SEAL_WRITE
+can be achieved, by using
+.BR F_SEAL_FUTURE_WRITE
+which will prevent future writes via
+.BR mmap (2)
+and
+.BR write (2)
+from succeeding, while keeping existing shared writable mappings).
 .IP 4.
 A second process obtains a file descriptor for the
 .BR tmpfs (5)
@@ -425,6 +433,7 @@ main(int argc, char *argv[])
         fprintf(stderr, "\et\etg \- F_SEAL_GROW\en");
         fprintf(stderr, "\et\ets \- F_SEAL_SHRINK\en");
         fprintf(stderr, "\et\etw \- F_SEAL_WRITE\en");
+        fprintf(stderr, "\et\etW \- F_SEAL_FUTURE_WRITE\en");
         fprintf(stderr, "\et\etS \- F_SEAL_SEAL\en");
         exit(EXIT_FAILURE);
     }
@@ -463,6 +472,8 @@ main(int argc, char *argv[])
             seals |= F_SEAL_SHRINK;
         if (strchr(seals_arg, \(aqw\(aq) != NULL)
             seals |= F_SEAL_WRITE;
+        if (strchr(seals_arg, \(aqW\(aq) != NULL)
+            seals |= F_SEAL_FUTURE_WRITE;
         if (strchr(seals_arg, \(aqS\(aq) != NULL)
             seals |= F_SEAL_SEAL;
 
@@ -518,6 +529,8 @@ main(int argc, char *argv[])
         printf(" GROW");
     if (seals & F_SEAL_WRITE)
         printf(" WRITE");
+    if (seals & F_SEAL_FUTURE_WRITE)
+        printf(" FUTURE_WRITE");
     if (seals & F_SEAL_SHRINK)
         printf(" SHRINK");
     printf("\en");
-- 
2.21.0.360.g471c308f928-goog

^ permalink raw reply	[flat|nested] 3+ messages in thread

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-- links below jump to the message on this page --
2019-03-14 21:48 [PATCH -manpage 0/2] Joel Fernandes (Google)
2019-03-14 21:48 ` [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal Joel Fernandes (Google)
2019-03-14 21:48 ` [PATCH -manpage 2/2] memfd_create.2: " Joel Fernandes (Google)

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