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, 84 insertions, 0 deletions

diff --git a/arch/arm/mm/tlb.c b/arch/arm/mm/tlb.c
new file mode 100644
index 000000000..423597931
--- /dev/null
+++ b/arch/arm/mm/tlb.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright 2024 Google LLC
+// Author: Ard Biesheuvel <ardb@google.com>
+
+#include <linux/types.h>
+#include <asm/tlbflush.h>
+
+#ifdef CONFIG_CPU_TLB_V4WT
+void v4_flush_user_tlb_range(unsigned long, unsigned long, struct vm_area_struct *);
+void v4_flush_kern_tlb_range(unsigned long, unsigned long);
+
+struct cpu_tlb_fns v4_tlb_fns __initconst = {
+	.flush_user_range	= v4_flush_user_tlb_range,
+	.flush_kern_range	= v4_flush_kern_tlb_range,
+	.tlb_flags		= v4_tlb_flags,
+};
+#endif
+
+#ifdef CONFIG_CPU_TLB_V4WB
+void v4wb_flush_user_tlb_range(unsigned long, unsigned long, struct vm_area_struct *);
+void v4wb_flush_kern_tlb_range(unsigned long, unsigned long);
+
+struct cpu_tlb_fns v4wb_tlb_fns __initconst = {
+	.flush_user_range	= v4wb_flush_user_tlb_range,
+	.flush_kern_range	= v4wb_flush_kern_tlb_range,
+	.tlb_flags		= v4wb_tlb_flags,
+};
+#endif
+
+#if defined(CONFIG_CPU_TLB_V4WBI) || defined(CONFIG_CPU_TLB_FEROCEON)
+void v4wbi_flush_user_tlb_range(unsigned long, unsigned long, struct vm_area_struct *);
+void v4wbi_flush_kern_tlb_range(unsigned long, unsigned long);
+
+struct cpu_tlb_fns v4wbi_tlb_fns __initconst = {
+	.flush_user_range	= v4wbi_flush_user_tlb_range,
+	.flush_kern_range	= v4wbi_flush_kern_tlb_range,
+	.tlb_flags		= v4wbi_tlb_flags,
+};
+#endif
+
+#ifdef CONFIG_CPU_TLB_V6
+void v6wbi_flush_user_tlb_range(unsigned long, unsigned long, struct vm_area_struct *);
+void v6wbi_flush_kern_tlb_range(unsigned long, unsigned long);
+
+struct cpu_tlb_fns v6wbi_tlb_fns __initconst = {
+	.flush_user_range	= v6wbi_flush_user_tlb_range,
+	.flush_kern_range	= v6wbi_flush_kern_tlb_range,
+	.tlb_flags		= v6wbi_tlb_flags,
+};
+#endif
+
+#ifdef CONFIG_CPU_TLB_V7
+void v7wbi_flush_user_tlb_range(unsigned long, unsigned long, struct vm_area_struct *);
+void v7wbi_flush_kern_tlb_range(unsigned long, unsigned long);
+
+struct cpu_tlb_fns v7wbi_tlb_fns __initconst = {
+	.flush_user_range	= v7wbi_flush_user_tlb_range,
+	.flush_kern_range	= v7wbi_flush_kern_tlb_range,
+	.tlb_flags		= IS_ENABLED(CONFIG_SMP) ? v7wbi_tlb_flags_smp
+							 : v7wbi_tlb_flags_up,
+};
+
+#ifdef CONFIG_SMP_ON_UP
+/* This will be run-time patched so the offset better be right */
+static_assert(offsetof(struct cpu_tlb_fns, tlb_flags) == 8);
+
+asm("	.pushsection	\".alt.smp.init\", \"a\"		\n" \
+    "	.align		2					\n" \
+    "	.long		v7wbi_tlb_fns + 8 - .			\n" \
+    "	.long "  	__stringify(v7wbi_tlb_flags_up) "	\n" \
+    "	.popsection						\n");
+#endif
+#endif
+
+#ifdef CONFIG_CPU_TLB_FA
+void fa_flush_user_tlb_range(unsigned long, unsigned long, struct vm_area_struct *);
+void fa_flush_kern_tlb_range(unsigned long, unsigned long);
+
+struct cpu_tlb_fns fa_tlb_fns __initconst = {
+	.flush_user_range	= fa_flush_user_tlb_range,
+	.flush_kern_range	= fa_flush_kern_tlb_range,
+	.tlb_flags		= fa_tlb_flags,
+};
+#endif