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, 87 insertions, 0 deletions

diff --git a/arch/microblaze/lib/umodsi3.S b/arch/microblaze/lib/umodsi3.S
new file mode 100644
index 000000000..f4b814e88
--- /dev/null
+++ b/arch/microblaze/lib/umodsi3.S
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/linkage.h>
+
+/*
+ * Unsigned modulo operation for 32 bit integers.
+ *	Input :	op1 in Reg r5
+ *		op2 in Reg r6
+ *	Output: op1 mod op2 in Reg r3
+ */
+
+	.text
+	.globl	__umodsi3
+	.type __umodsi3, @function
+	.ent __umodsi3
+
+__umodsi3:
+	.frame	r1, 0, r15
+
+	addik	r1, r1, -12
+	swi	r29, r1, 0
+	swi	r30, r1, 4
+	swi	r31, r1, 8
+
+	beqi	r6, div_by_zero /* div_by_zero - division error */
+	beqid	r5, result_is_zero /* result is zero */
+	addik	r3, r0, 0 /* clear div */
+	addik	r30, r0, 0 /* clear mod */
+	addik	r29, r0, 32 /* initialize the loop count */
+
+/* check if r6 and r5 are equal /* if yes, return 0 */
+	rsub	r18, r5, r6
+	beqi	r18, return_here
+
+/* check if (uns)r6 is greater than (uns)r5. in that case, just return r5 */
+	xor	r18, r5, r6
+	bgeid	r18, 16
+	addik	r3, r5, 0
+	blti	r6, return_here
+	bri	$lcheckr6
+	rsub	r18, r5, r6 /* microblazecmp */
+	bgti	r18, return_here
+
+/* if r6 [bit 31] is set, then return result as r5-r6 */
+$lcheckr6:
+	bgtid	r6, div0
+	addik	r3, r0, 0
+	addik	r18, r0, 0x7fffffff
+	and	r5, r5, r18
+	and	r6, r6, r18
+	brid	return_here
+	rsub	r3, r6, r5
+/* first part: try to find the first '1' in the r5 */
+div0:
+	blti	r5, div2
+div1:
+	add	r5, r5, r5 /* left shift logical r5 */
+	bgeid	r5, div1
+	addik	r29, r29, -1
+div2:
+	/* left shift logical r5 get the '1' into the carry */
+	add	r5, r5, r5
+	addc	r3, r3, r3 /* move that bit into the mod register */
+	rsub	r31, r6, r3 /* try to subtract (r3 a r6) */
+	blti	r31, mod_too_small
+	/* move the r31 to mod since the result was positive */
+	or	r3, r0, r31
+	addik	r30, r30, 1
+mod_too_small:
+	addik	r29, r29, -1
+	beqi	r29, loop_end
+	add	r30, r30, r30 /* shift in the '1' into div */
+	bri	div2 /* div2 */
+loop_end:
+	bri	return_here
+div_by_zero:
+result_is_zero:
+	or	r3, r0, r0 /* set result to 0 */
+return_here:
+/* restore values of csrs and that of r3 and the divisor and the dividend */
+	lwi	r29, r1, 0
+	lwi	r30, r1, 4
+	lwi	r31, r1, 8
+	rtsd	r15, 8
+	addik	r1, r1, 12
+
+.size __umodsi3, . - __umodsi3
+.end __umodsi3