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/mach-spear/pl080.c b/arch/arm/mach-spear/pl080.c
new file mode 100644
index 000000000..47243a815
--- /dev/null
+++ b/arch/arm/mach-spear/pl080.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * arch/arm/plat-spear/pl080.c
+ *
+ * DMAC pl080 definitions for SPEAr platform
+ *
+ * Copyright (C) 2012 ST Microelectronics
+ * Viresh Kumar <vireshk@kernel.org>
+ */
+
+#include <linux/amba/pl08x.h>
+#include <linux/amba/bus.h>
+#include <linux/bug.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/spinlock_types.h>
+#include "spear.h"
+#include "misc_regs.h"
+#include "pl080.h"
+
+static spinlock_t lock = __SPIN_LOCK_UNLOCKED(x);
+
+struct {
+	unsigned char busy;
+	unsigned char val;
+} signals[16] = {{0, 0}, };
+
+int pl080_get_signal(const struct pl08x_channel_data *cd)
+{
+	unsigned int signal = cd->min_signal, val;
+	unsigned long flags;
+
+	spin_lock_irqsave(&lock, flags);
+
+	/* Return if signal is already acquired by somebody else */
+	if (signals[signal].busy &&
+			(signals[signal].val != cd->muxval)) {
+		spin_unlock_irqrestore(&lock, flags);
+		return -EBUSY;
+	}
+
+	/* If acquiring for the first time, configure it */
+	if (!signals[signal].busy) {
+		val = readl(DMA_CHN_CFG);
+
+		/*
+		 * Each request line has two bits in DMA_CHN_CFG register. To
+		 * goto the bits of current request line, do left shift of
+		 * value by 2 * signal number.
+		 */
+		val &= ~(0x3 << (signal * 2));
+		val |= cd->muxval << (signal * 2);
+		writel(val, DMA_CHN_CFG);
+	}
+
+	signals[signal].busy++;
+	signals[signal].val = cd->muxval;
+	spin_unlock_irqrestore(&lock, flags);
+
+	return signal;
+}
+
+void pl080_put_signal(const struct pl08x_channel_data *cd, int signal)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&lock, flags);
+
+	/* if signal is not used */
+	if (!signals[signal].busy)
+		BUG();
+
+	signals[signal].busy--;
+
+	spin_unlock_irqrestore(&lock, flags);
+}