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, 43 insertions, 0 deletions

diff --git a/arch/powerpc/sysdev/grackle.c b/arch/powerpc/sysdev/grackle.c
new file mode 100644
index 000000000..7dce8278b
--- /dev/null
+++ b/arch/powerpc/sysdev/grackle.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Functions for setting up and using a MPC106 northbridge
+ * Extracted from arch/powerpc/platforms/powermac/pci.c.
+ *
+ * Copyright (C) 2003 Benjamin Herrenschmuidt (benh@kernel.crashing.org)
+ * Copyright (C) 1997 Paul Mackerras (paulus@samba.org)
+ */
+#include <linux/kernel.h>
+#include <linux/pci.h>
+#include <linux/init.h>
+#include <linux/of.h>
+
+#include <asm/io.h>
+#include <asm/pci-bridge.h>
+#include <asm/grackle.h>
+
+#define GRACKLE_CFA(b, d, o)	(0x80 | ((b) << 8) | ((d) << 16) \
+				 | (((o) & ~3) << 24))
+
+#define GRACKLE_PICR1_LOOPSNOOP		0x00000010
+
+static inline void grackle_set_loop_snoop(struct pci_controller *bp, int enable)
+{
+	unsigned int val;
+
+	out_be32(bp->cfg_addr, GRACKLE_CFA(0, 0, 0xa8));
+	val = in_le32(bp->cfg_data);
+	val = enable? (val | GRACKLE_PICR1_LOOPSNOOP) :
+		(val & ~GRACKLE_PICR1_LOOPSNOOP);
+	out_be32(bp->cfg_addr, GRACKLE_CFA(0, 0, 0xa8));
+	out_le32(bp->cfg_data, val);
+	(void)in_le32(bp->cfg_data);
+}
+
+void __init setup_grackle(struct pci_controller *hose)
+{
+	setup_indirect_pci(hose, 0xfec00000, 0xfee00000, 0);
+	if (of_machine_is_compatible("PowerMac1,1"))
+		pci_add_flags(PCI_REASSIGN_ALL_BUS);
+	if (of_machine_is_compatible("AAPL,PowerBook1998"))
+		grackle_set_loop_snoop(hose, 1);
+}