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, 117 insertions, 0 deletions

diff --git a/include/clocksource/hyperv_timer.h b/include/clocksource/hyperv_timer.h
new file mode 100644
index 000000000..d48dd4176
--- /dev/null
+++ b/include/clocksource/hyperv_timer.h
@@ -0,0 +1,117 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Definitions for the clocksource provided by the Hyper-V
+ * hypervisor to guest VMs, as described in the Hyper-V Top
+ * Level Functional Spec (TLFS).
+ *
+ * Copyright (C) 2019, Microsoft, Inc.
+ *
+ * Author:  Michael Kelley <mikelley@microsoft.com>
+ */
+
+#ifndef __CLKSOURCE_HYPERV_TIMER_H
+#define __CLKSOURCE_HYPERV_TIMER_H
+
+#include <linux/clocksource.h>
+#include <linux/math64.h>
+#include <hyperv/hvhdk.h>
+
+#define HV_MAX_MAX_DELTA_TICKS 0xffffffff
+#define HV_MIN_DELTA_TICKS 1
+
+#ifdef CONFIG_HYPERV_TIMER
+
+#include <asm/hyperv_timer.h>
+
+/* Routines called by the VMbus driver */
+extern int hv_stimer_alloc(bool have_percpu_irqs);
+extern int hv_stimer_cleanup(unsigned int cpu);
+extern void hv_stimer_legacy_init(unsigned int cpu, int sint);
+extern void hv_stimer_legacy_cleanup(unsigned int cpu);
+extern void hv_stimer_global_cleanup(void);
+extern void hv_stimer0_isr(void);
+
+extern void hv_init_clocksource(void);
+extern void hv_remap_tsc_clocksource(void);
+
+extern unsigned long hv_get_tsc_pfn(void);
+extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
+
+extern void hv_adj_sched_clock_offset(u64 offset);
+
+static __always_inline bool
+hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
+		     u64 *cur_tsc, u64 *time)
+{
+	u64 scale, offset;
+	u32 sequence;
+
+	/*
+	 * The protocol for reading Hyper-V TSC page is specified in Hypervisor
+	 * Top-Level Functional Specification ver. 3.0 and above. To get the
+	 * reference time we must do the following:
+	 * - READ ReferenceTscSequence
+	 *   A special '0' value indicates the time source is unreliable and we
+	 *   need to use something else. The currently published specification
+	 *   versions (up to 4.0b) contain a mistake and wrongly claim '-1'
+	 *   instead of '0' as the special value, see commit c35b82ef0294.
+	 * - ReferenceTime =
+	 *        ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
+	 * - READ ReferenceTscSequence again. In case its value has changed
+	 *   since our first reading we need to discard ReferenceTime and repeat
+	 *   the whole sequence as the hypervisor was updating the page in
+	 *   between.
+	 */
+	do {
+		sequence = READ_ONCE(tsc_pg->tsc_sequence);
+		if (!sequence)
+			return false;
+		/*
+		 * Make sure we read sequence before we read other values from
+		 * TSC page.
+		 */
+		smp_rmb();
+
+		scale = READ_ONCE(tsc_pg->tsc_scale);
+		offset = READ_ONCE(tsc_pg->tsc_offset);
+		*cur_tsc = hv_get_raw_timer();
+
+		/*
+		 * Make sure we read sequence after we read all other values
+		 * from TSC page.
+		 */
+		smp_rmb();
+
+	} while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
+
+	*time = mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
+	return true;
+}
+
+#else /* CONFIG_HYPERV_TIMER */
+static inline unsigned long hv_get_tsc_pfn(void)
+{
+	return 0;
+}
+
+static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
+{
+	return NULL;
+}
+
+static __always_inline bool
+hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc, u64 *time)
+{
+	return false;
+}
+
+static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
+static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {}
+static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {}
+static inline void hv_stimer_global_cleanup(void) {}
+static inline void hv_stimer0_isr(void) {}
+
+#endif /* CONFIG_HYPERV_TIMER */
+
+#endif