* [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; 5+ 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] 5+ 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) 2020-02-08 11:58 ` Michael Kerrisk (man-pages) 2019-03-14 21:48 ` [PATCH -manpage 2/2] memfd_create.2: " Joel Fernandes (Google) 1 sibling, 1 reply; 5+ 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 related [flat|nested] 5+ messages in thread
* Re: [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal 2019-03-14 21:48 ` [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal Joel Fernandes (Google) @ 2020-02-08 11:58 ` Michael Kerrisk (man-pages) 0 siblings, 0 replies; 5+ messages in thread From: Michael Kerrisk (man-pages) @ 2020-02-08 11:58 UTC (permalink / raw) To: Joel Fernandes (Google), linux-kernel Cc: mtk.manpages, 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 Hello Joel, On 3/14/19 10:48 PM, Joel Fernandes (Google) wrote: > 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> Thanks. Patch (finally) applied! Cheers, Michael > --- > 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 > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ ^ permalink raw reply [flat|nested] 5+ 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) 2020-02-08 11:58 ` Michael Kerrisk (man-pages) 1 sibling, 1 reply; 5+ 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 related [flat|nested] 5+ messages in thread
* Re: [PATCH -manpage 2/2] memfd_create.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal 2019-03-14 21:48 ` [PATCH -manpage 2/2] memfd_create.2: " Joel Fernandes (Google) @ 2020-02-08 11:58 ` Michael Kerrisk (man-pages) 0 siblings, 0 replies; 5+ messages in thread From: Michael Kerrisk (man-pages) @ 2020-02-08 11:58 UTC (permalink / raw) To: Joel Fernandes (Google), linux-kernel Cc: mtk.manpages, 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 Hello Joel, On 3/14/19 10:48 PM, Joel Fernandes (Google) wrote: > 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> Thanks! Patch applied Cheers, Michael > --- > 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"); > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2020-02-08 11:58 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- 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) 2020-02-08 11:58 ` Michael Kerrisk (man-pages) 2019-03-14 21:48 ` [PATCH -manpage 2/2] memfd_create.2: " Joel Fernandes (Google) 2020-02-08 11:58 ` Michael Kerrisk (man-pages)
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