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, 76 insertions, 0 deletions

diff --git a/arch/arm/lib/io-readsl.S b/arch/arm/lib/io-readsl.S
new file mode 100644
index 000000000..d9f6b372b
--- /dev/null
+++ b/arch/arm/lib/io-readsl.S
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/arch/arm/lib/io-readsl.S
+ *
+ *  Copyright (C) 1995-2000 Russell King
+ */
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+ENTRY(__raw_readsl)
+		teq	r2, #0		@ do we have to check for the zero len?
+		reteq	lr
+		ands	ip, r1, #3
+		bne	3f
+
+		subs	r2, r2, #4
+		bmi	2f
+		stmfd	sp!, {r4, lr}
+1:		ldr	r3, [r0, #0]
+		ldr	r4, [r0, #0]
+		ldr	ip, [r0, #0]
+		ldr	lr, [r0, #0]
+		subs	r2, r2, #4
+		stmia	r1!, {r3, r4, ip, lr}
+		bpl	1b
+		ldmfd	sp!, {r4, lr}
+2:		movs	r2, r2, lsl #31
+		ldrcs	r3, [r0, #0]
+		ldrcs	ip, [r0, #0]
+		stmiacs	r1!, {r3, ip}
+		ldrne	r3, [r0, #0]
+		strne	r3, [r1, #0]
+		ret	lr
+
+3:		ldr	r3, [r0]
+		cmp	ip, #2
+		mov	ip, r3, get_byte_0
+		strb	ip, [r1], #1
+		bgt	6f
+		mov	ip, r3, get_byte_1
+		strb	ip, [r1], #1
+		beq	5f
+		mov	ip, r3, get_byte_2
+		strb	ip, [r1], #1
+
+4:		subs	r2, r2, #1
+		mov	ip, r3, lspull #24
+		ldrne	r3, [r0]
+		orrne	ip, ip, r3, lspush #8
+		strne	ip, [r1], #4
+		bne	4b
+		b	8f
+
+5:		subs	r2, r2, #1
+		mov	ip, r3, lspull #16
+		ldrne	r3, [r0]
+		orrne	ip, ip, r3, lspush #16
+		strne	ip, [r1], #4
+		bne	5b
+		b	7f
+
+6:		subs	r2, r2, #1
+		mov	ip, r3, lspull #8
+		ldrne	r3, [r0]
+		orrne	ip, ip, r3, lspush #24
+		strne	ip, [r1], #4
+		bne	6b
+
+		mov	r3, ip, get_byte_2
+		strb	r3, [r1, #2]
+7:		mov	r3, ip, get_byte_1
+		strb	r3, [r1, #1]
+8:		mov	r3, ip, get_byte_0
+		strb	r3, [r1, #0]
+		ret	lr
+ENDPROC(__raw_readsl)