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, 53 insertions, 0 deletions

diff --git a/arch/mips/kvm/hypcall.c b/arch/mips/kvm/hypcall.c
new file mode 100644
index 000000000..830634351
--- /dev/null
+++ b/arch/mips/kvm/hypcall.c
@@ -0,0 +1,53 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * KVM/MIPS: Hypercall handling.
+ *
+ * Copyright (C) 2015  Imagination Technologies Ltd.
+ */
+
+#include <linux/kernel.h>
+#include <linux/kvm_host.h>
+#include <linux/kvm_para.h>
+
+#define MAX_HYPCALL_ARGS	4
+
+enum emulation_result kvm_mips_emul_hypcall(struct kvm_vcpu *vcpu,
+					    union mips_instruction inst)
+{
+	unsigned int code = (inst.co_format.code >> 5) & 0x3ff;
+
+	kvm_debug("[%#lx] HYPCALL %#03x\n", vcpu->arch.pc, code);
+
+	switch (code) {
+	case 0:
+		return EMULATE_HYPERCALL;
+	default:
+		return EMULATE_FAIL;
+	};
+}
+
+static int kvm_mips_hypercall(struct kvm_vcpu *vcpu, unsigned long num,
+			      const unsigned long *args, unsigned long *hret)
+{
+	/* Report unimplemented hypercall to guest */
+	*hret = -KVM_ENOSYS;
+	return RESUME_GUEST;
+}
+
+int kvm_mips_handle_hypcall(struct kvm_vcpu *vcpu)
+{
+	unsigned long num, args[MAX_HYPCALL_ARGS];
+
+	/* read hypcall number and arguments */
+	num = vcpu->arch.gprs[2];	/* v0 */
+	args[0] = vcpu->arch.gprs[4];	/* a0 */
+	args[1] = vcpu->arch.gprs[5];	/* a1 */
+	args[2] = vcpu->arch.gprs[6];	/* a2 */
+	args[3] = vcpu->arch.gprs[7];	/* a3 */
+
+	return kvm_mips_hypercall(vcpu, num,
+				  args, &vcpu->arch.gprs[2] /* v0 */);
+}