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, 70 insertions, 0 deletions

diff --git a/arch/mips/mm/cex-oct.S b/arch/mips/mm/cex-oct.S
new file mode 100644
index 000000000..9029092aa
--- /dev/null
+++ b/arch/mips/mm/cex-oct.S
@@ -0,0 +1,70 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2006 Cavium Networks
+ * Cache error handler
+ */
+
+#include <asm/asm.h>
+#include <asm/regdef.h>
+#include <asm/mipsregs.h>
+#include <asm/stackframe.h>
+
+/*
+ * Handle cache error. Indicate to the second level handler whether
+ * the exception is recoverable.
+ */
+	LEAF(except_vec2_octeon)
+
+	.set	push
+	.set	mips64r2
+	.set	noreorder
+	.set	noat
+
+
+	/* due to an errata we need to read the COP0 CacheErr (Dcache)
+	 * before any cache/DRAM access	 */
+
+	rdhwr	k0, $0	      /* get core_id */
+	PTR_LA	k1, cache_err_dcache
+	sll	k0, k0, 3
+	PTR_ADDU k1, k0, k1    /* k1 = &cache_err_dcache[core_id] */
+
+	dmfc0	k0, CP0_CACHEERR, 1
+	sd	k0, (k1)
+	dmtc0	$0, CP0_CACHEERR, 1
+
+	/* check whether this is a nested exception */
+	mfc0	k1, CP0_STATUS
+	andi	k1, k1, ST0_EXL
+	beqz	k1, 1f
+	 nop
+	j	cache_parity_error_octeon_non_recoverable
+	 nop
+
+	/* exception is recoverable */
+1:	j	handle_cache_err
+	 nop
+
+	.set	pop
+	END(except_vec2_octeon)
+
+ /* We need to jump to handle_cache_err so that the previous handler
+  * can fit within 0x80 bytes. We also move from 0xFFFFFFFFAXXXXXXX
+  * space (uncached) to the 0xFFFFFFFF8XXXXXXX space (cached).	*/
+	LEAF(handle_cache_err)
+	.set	push
+	.set	noreorder
+	.set	noat
+
+	SAVE_ALL
+	KMODE
+	jal	cache_parity_error_octeon_recoverable
+	nop
+	j	ret_from_exception
+	nop
+
+	.set pop
+	END(handle_cache_err)