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, 147 insertions, 0 deletions

diff --git a/arch/x86/lib/msr.c b/arch/x86/lib/msr.c
new file mode 100644
index 000000000..dfdd1da89
--- /dev/null
+++ b/arch/x86/lib/msr.c
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/export.h>
+#include <linux/kvm_types.h>
+#include <linux/percpu.h>
+#include <linux/preempt.h>
+#include <asm/msr.h>
+#define CREATE_TRACE_POINTS
+#include <asm/msr-trace.h>
+
+struct msr __percpu *msrs_alloc(void)
+{
+	struct msr __percpu *msrs = NULL;
+
+	msrs = alloc_percpu(struct msr);
+	if (!msrs) {
+		pr_warn("%s: error allocating msrs\n", __func__);
+		return NULL;
+	}
+
+	return msrs;
+}
+EXPORT_SYMBOL(msrs_alloc);
+
+void msrs_free(struct msr __percpu *msrs)
+{
+	free_percpu(msrs);
+}
+EXPORT_SYMBOL(msrs_free);
+
+/**
+ * msr_read - Read an MSR with error handling
+ * @msr: MSR to read
+ * @m: value to read into
+ *
+ * It returns read data only on success, otherwise it doesn't change the output
+ * argument @m.
+ *
+ * Return: %0 for success, otherwise an error code
+ */
+static int msr_read(u32 msr, struct msr *m)
+{
+	int err;
+	u64 val;
+
+	err = rdmsrq_safe(msr, &val);
+	if (!err)
+		m->q = val;
+
+	return err;
+}
+
+/**
+ * msr_write - Write an MSR with error handling
+ *
+ * @msr: MSR to write
+ * @m: value to write
+ *
+ * Return: %0 for success, otherwise an error code
+ */
+static int msr_write(u32 msr, struct msr *m)
+{
+	return wrmsrq_safe(msr, m->q);
+}
+
+static inline int __flip_bit(u32 msr, u8 bit, bool set)
+{
+	struct msr m, m1;
+	int err = -EINVAL;
+
+	if (bit > 63)
+		return err;
+
+	err = msr_read(msr, &m);
+	if (err)
+		return err;
+
+	m1 = m;
+	if (set)
+		m1.q |=  BIT_64(bit);
+	else
+		m1.q &= ~BIT_64(bit);
+
+	if (m1.q == m.q)
+		return 0;
+
+	err = msr_write(msr, &m1);
+	if (err)
+		return err;
+
+	return 1;
+}
+
+/**
+ * msr_set_bit - Set @bit in a MSR @msr.
+ * @msr: MSR to write
+ * @bit: bit number to set
+ *
+ * Return:
+ * * < 0: An error was encountered.
+ * * = 0: Bit was already set.
+ * * > 0: Hardware accepted the MSR write.
+ */
+int msr_set_bit(u32 msr, u8 bit)
+{
+	return __flip_bit(msr, bit, true);
+}
+EXPORT_SYMBOL_FOR_KVM(msr_set_bit);
+
+/**
+ * msr_clear_bit - Clear @bit in a MSR @msr.
+ * @msr: MSR to write
+ * @bit: bit number to clear
+ *
+ * Return:
+ * * < 0: An error was encountered.
+ * * = 0: Bit was already cleared.
+ * * > 0: Hardware accepted the MSR write.
+ */
+int msr_clear_bit(u32 msr, u8 bit)
+{
+	return __flip_bit(msr, bit, false);
+}
+EXPORT_SYMBOL_FOR_KVM(msr_clear_bit);
+
+#ifdef CONFIG_TRACEPOINTS
+void do_trace_write_msr(u32 msr, u64 val, int failed)
+{
+	trace_write_msr(msr, val, failed);
+}
+EXPORT_SYMBOL(do_trace_write_msr);
+EXPORT_TRACEPOINT_SYMBOL(write_msr);
+
+void do_trace_read_msr(u32 msr, u64 val, int failed)
+{
+	trace_read_msr(msr, val, failed);
+}
+EXPORT_SYMBOL(do_trace_read_msr);
+EXPORT_TRACEPOINT_SYMBOL(read_msr);
+
+void do_trace_rdpmc(u32 msr, u64 val, int failed)
+{
+	trace_rdpmc(msr, val, failed);
+}
+EXPORT_SYMBOL(do_trace_rdpmc);
+EXPORT_TRACEPOINT_SYMBOL(rdpmc);
+
+#endif