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, 67 insertions, 0 deletions

diff --git a/arch/hexagon/lib/divsi3.S b/arch/hexagon/lib/divsi3.S
new file mode 100644
index 000000000..783e09424
--- /dev/null
+++ b/arch/hexagon/lib/divsi3.S
@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2021, The Linux Foundation. All rights reserved.
+ */
+
+#include <linux/linkage.h>
+
+SYM_FUNC_START(__hexagon_divsi3)
+        {
+                p0 = cmp.gt(r0,#-1)
+                p1 = cmp.gt(r1,#-1)
+                r3:2 = vabsw(r1:0)
+        }
+        {
+                p3 = xor(p0,p1)
+                r4 = sub(r2,r3)
+                r6 = cl0(r2)
+                p0 = cmp.gtu(r3,r2)
+        }
+        {
+                r0 = mux(p3,#-1,#1)
+                r7 = cl0(r3)
+                p1 = cmp.gtu(r3,r4)
+        }
+        {
+                r0 = mux(p0,#0,r0)
+                p0 = or(p0,p1)
+                if (p0.new) jumpr:nt r31
+                r6 = sub(r7,r6)
+        }
+        {
+                r7 = r6
+                r5:4 = combine(#1,r3)
+                r6 = add(#1,lsr(r6,#1))
+                p0 = cmp.gtu(r6,#4)
+        }
+        {
+                r5:4 = vaslw(r5:4,r7)
+                if (!p0) r6 = #3
+        }
+        {
+                loop0(1f,r6)
+                r7:6 = vlsrw(r5:4,#1)
+                r1:0 = #0
+        }
+        .falign
+1:
+        {
+                r5:4 = vlsrw(r5:4,#2)
+                if (!p0.new) r0 = add(r0,r5)
+                if (!p0.new) r2 = sub(r2,r4)
+                p0 = cmp.gtu(r4,r2)
+        }
+        {
+                r7:6 = vlsrw(r7:6,#2)
+                if (!p0.new) r0 = add(r0,r7)
+                if (!p0.new) r2 = sub(r2,r6)
+                p0 = cmp.gtu(r6,r2)
+        }:endloop0
+        {
+                if (!p0) r0 = add(r0,r7)
+        }
+        {
+                if (p3) r0 = sub(r1,r0)
+                jumpr r31
+        }
+SYM_FUNC_END(__hexagon_divsi3)