selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 64 insertions, 0 deletions

diff --git a/fs/romfs/Kconfig b/fs/romfs/Kconfig
new file mode 100644
index 000000000..f24a96a33
--- /dev/null
+++ b/fs/romfs/Kconfig
@@ -0,0 +1,64 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config ROMFS_FS
+	tristate "ROM file system support"
+	depends on BLOCK || MTD
+	help
+	  This is a very small read-only file system mainly intended for
+	  initial ram disks of installation disks, but it could be used for
+	  other read-only media as well.  Read
+	  <file:Documentation/filesystems/romfs.rst> for details.
+
+	  To compile this file system support as a module, choose M here: the
+	  module will be called romfs.  Note that the file system of your
+	  root partition (the one containing the directory /) cannot be a
+	  module.
+
+	  If you don't know whether you need it, then you don't need it:
+	  answer N.
+
+#
+# Select the backing stores to be supported
+#
+choice
+	prompt "RomFS backing stores"
+	depends on ROMFS_FS
+	default ROMFS_BACKED_BY_BLOCK
+	help
+	  Select the backing stores to be supported.
+
+config ROMFS_BACKED_BY_BLOCK
+	bool "Block device-backed ROM file system support"
+	depends on BLOCK
+	help
+	  This permits ROMFS to use block devices buffered through the page
+	  cache as the medium from which to retrieve data.  It does not allow
+	  direct mapping of the medium.
+
+	  If unsure, answer Y.
+
+config ROMFS_BACKED_BY_MTD
+	bool "MTD-backed ROM file system support"
+	depends on MTD=y || (ROMFS_FS=m && MTD)
+	help
+	  This permits ROMFS to use MTD based devices directly, without the
+	  intercession of the block layer (which may have been disabled).  It
+	  also allows direct mapping of MTD devices through romfs files under
+	  NOMMU conditions if the underlying device is directly addressable by
+	  the CPU.
+
+	  If unsure, answer Y.
+
+config ROMFS_BACKED_BY_BOTH
+	bool "Both the above"
+	depends on BLOCK && (MTD=y || (ROMFS_FS=m && MTD))
+endchoice
+
+
+config ROMFS_ON_BLOCK
+	bool
+	default y if ROMFS_BACKED_BY_BLOCK || ROMFS_BACKED_BY_BOTH
+	select BUFFER_HEAD
+
+config ROMFS_ON_MTD
+	bool
+	default y if ROMFS_BACKED_BY_MTD || ROMFS_BACKED_BY_BOTH