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/arm64/lib/memchr.S b/arch/arm64/lib/memchr.S
new file mode 100644
index 000000000..37a9f2a4f
--- /dev/null
+++ b/arch/arm64/lib/memchr.S
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 Arm Ltd.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/*
+ * Find a character in an area of memory.
+ *
+ * Parameters:
+ *	x0 - buf
+ *	x1 - c
+ *	x2 - n
+ * Returns:
+ *	x0 - address of first occurrence of 'c' or 0
+ */
+
+#define L(label) .L ## label
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+
+#define srcin		x0
+#define chrin		w1
+#define cntin		x2
+
+#define result		x0
+
+#define wordcnt		x3
+#define rep01		x4
+#define repchr		x5
+#define cur_word	x6
+#define cur_byte	w6
+#define tmp		x7
+#define tmp2		x8
+
+	.p2align 4
+	nop
+SYM_FUNC_START(__pi_memchr)
+	and	chrin, chrin, #0xff
+	lsr	wordcnt, cntin, #3
+	cbz	wordcnt, L(byte_loop)
+	mov	rep01, #REP8_01
+	mul	repchr, x1, rep01
+	and	cntin, cntin, #7
+L(word_loop):
+	ldr	cur_word, [srcin], #8
+	sub	wordcnt, wordcnt, #1
+	eor	cur_word, cur_word, repchr
+	sub	tmp, cur_word, rep01
+	orr	tmp2, cur_word, #REP8_7f
+	bics	tmp, tmp, tmp2
+	b.ne	L(found_word)
+	cbnz	wordcnt, L(word_loop)
+L(byte_loop):
+	cbz	cntin, L(not_found)
+	ldrb	cur_byte, [srcin], #1
+	sub	cntin, cntin, #1
+	cmp	cur_byte, chrin
+	b.ne	L(byte_loop)
+	sub	srcin, srcin, #1
+	ret
+L(found_word):
+CPU_LE(	rev	tmp, tmp)
+	clz	tmp, tmp
+	sub	tmp, tmp, #64
+	add	result, srcin, tmp, asr #3
+	ret
+L(not_found):
+	mov	result, #0
+	ret
+SYM_FUNC_END(__pi_memchr)
+SYM_FUNC_ALIAS_WEAK(memchr, __pi_memchr)
+EXPORT_SYMBOL_NOKASAN(memchr)