[LTP] [PATCH] lib: tst_fd: Add kernel version check to memfd_secret

[nobuhiro1.iwamatsu@toshiba.co.jp]

Hi,

Thanks for your review.

> -----Original Message-----
> From: Cyril Hrubis <chrubis@suse.cz>
> Sent: Tuesday, June 18, 2024 7:16 PM
> To: iwamatsu nobuhiro(岩松 信洋 ○ＤＩＴＣ□ＤＩＴ○ＯＳＴ)
> <nobuhiro1.iwamatsu@toshiba.co.jp>
> Cc: ltp@lists.linux.it
> Subject: Re: [PATCH] lib: tst_fd: Add kernel version check to memfd_secret
> 
> Hi!
> > memfd_secret is a syscall added since 5.14. On earlier kernels, tests
> > such as accept03, readahead01 and splice07 that use memfd_secret fail.
> > This adds a kernel version check to the tst_fd library when running
> > tests using memfd_secret.
> >
> > Test log on linux-5.10.162/arm32 with version 20240524:
> > ```
> > $ ./testcases/kernel/syscalls/accept/accept03
> > tst_test.c:1733: TINFO: LTP version: 20240524
> > tst_test.c:1617: TINFO: Timeout per run is 0h 00m 30s
> > accept03.c:58: TPASS: accept() on file : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on O_PATH file : EBADF (9)
> > accept03.c:58: TPASS: accept() on directory : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on /dev/zero : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on /proc/self/maps : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on pipe read end : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on pipe write end : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on epoll : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on eventfd : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on signalfd : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on timerfd : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on pidfd : ENOTSOCK (88)
> > tst_fd.c:151: TCONF: Skipping fanotify: ENOSYS (38)
> > accept03.c:58: TPASS: accept() on inotify : ENOTSOCK (88)
> > tst_fd.c:170: TCONF: Skipping userfaultfd: ENOSYS (38)
> > accept03.c:58: TPASS: accept() on perf event : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on io uring : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on bpf map : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on fsopen : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on fspick : ENOTSOCK (88)
> > accept03.c:58: TPASS: accept() on open_tree : EBADF (9)
> > accept03.c:58: TPASS: accept() on memfd : ENOTSOCK (88)
> > tst_test.c:1677: TBROK: Test killed by SIGILL!
> 
> This looks like a bug either in kernel or libc.

This is caused by __NR_memfd_secure being defined as -1 (0xffffffff)and "Illegal instruction" 
occurs when syscall() is executed. And this problem does not occur on x86_64. 
I cannot decide if this is a bug or not. I can't decide if this is a bug or not, because this behavior has
existed for a long time.

> 
> > Summary:
> > passed   20
> > failed   0
> > broken   1
> > skipped  2
> > warnings 0
> > ```
> >
> > Closed: #1145
> > Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
> > ---
> >  lib/tst_fd.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/lib/tst_fd.c b/lib/tst_fd.c index 6538a098c..53f583fa0
> > 100644
> > --- a/lib/tst_fd.c
> > +++ b/lib/tst_fd.c
> > @@ -255,8 +255,16 @@ static void open_memfd(struct tst_fd *fd)
> >
> >  static void open_memfd_secret(struct tst_fd *fd)  {
> > +	if ((tst_kvercmp(5, 14, 0)) < 0) {
> > +		tst_res(TINFO, "accept() on %s: Linux kernel version is before
> than v5.14", tst_fd_desc(fd));
> > +		errno = ENOSYS;
> > +		goto skip;
> > +	}
> > +
> >  	fd->fd = syscall(__NR_memfd_secret, 0);
> > +
> >  	if (fd->fd < 0) {
> > +skip:
> >  		tst_res(TCONF | TERRNO,
> >  			"Skipping %s", tst_fd_desc(fd));
> >  	}
> 
> And this looks like you are working around the bug.

Your point is correct...
I would suggest using tst_syscall() to check for syscall undefined instead
of this modification. How about this modification? 

```
--- a/lib/tst_fd.c
+++ b/lib/tst_fd.c
@@ -255,7 +255,8 @@ static void open_memfd(struct tst_fd *fd)

 static void open_memfd_secret(struct tst_fd *fd)
 {
-       fd->fd = syscall(__NR_memfd_secret, 0);
+       fd->fd = tst_syscall(__NR_memfd_secret, 0);
        if (fd->fd < 0) {
                tst_res(TCONF | TERRNO,
                        "Skipping %s", tst_fd_desc(fd));
```


Best regards,
  Nobuhiro