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, 102 insertions, 0 deletions

diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
new file mode 100644
index 000000000..fbf08b543
--- /dev/null
+++ b/arch/arm64/mm/flush.c
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Based on arch/arm/mm/flush.c
+ *
+ * Copyright (C) 1995-2002 Russell King
+ * Copyright (C) 2012 ARM Ltd.
+ */
+
+#include <linux/export.h>
+#include <linux/mm.h>
+#include <linux/libnvdimm.h>
+#include <linux/pagemap.h>
+
+#include <asm/cacheflush.h>
+#include <asm/cache.h>
+#include <asm/tlbflush.h>
+
+void sync_icache_aliases(unsigned long start, unsigned long end)
+{
+	if (icache_is_aliasing()) {
+		dcache_clean_pou(start, end);
+		icache_inval_all_pou();
+	} else {
+		/*
+		 * Don't issue kick_all_cpus_sync() after I-cache invalidation
+		 * for user mappings.
+		 */
+		caches_clean_inval_pou(start, end);
+	}
+}
+
+static void flush_ptrace_access(struct vm_area_struct *vma, unsigned long start,
+				unsigned long end)
+{
+	if (vma->vm_flags & VM_EXEC)
+		sync_icache_aliases(start, end);
+}
+
+/*
+ * Copy user data from/to a page which is mapped into a different processes
+ * address space.  Really, we want to allow our "user space" model to handle
+ * this.
+ */
+void copy_to_user_page(struct vm_area_struct *vma, struct page *page,
+		       unsigned long uaddr, void *dst, const void *src,
+		       unsigned long len)
+{
+	memcpy(dst, src, len);
+	flush_ptrace_access(vma, (unsigned long)dst, (unsigned long)dst + len);
+}
+
+void __sync_icache_dcache(pte_t pte)
+{
+	struct folio *folio = page_folio(pte_page(pte));
+
+	if (!test_bit(PG_dcache_clean, &folio->flags.f)) {
+		sync_icache_aliases((unsigned long)folio_address(folio),
+				    (unsigned long)folio_address(folio) +
+					    folio_size(folio));
+		set_bit(PG_dcache_clean, &folio->flags.f);
+	}
+}
+EXPORT_SYMBOL_GPL(__sync_icache_dcache);
+
+/*
+ * This function is called when a page has been modified by the kernel. Mark
+ * it as dirty for later flushing when mapped in user space (if executable,
+ * see __sync_icache_dcache).
+ */
+void flush_dcache_folio(struct folio *folio)
+{
+	if (test_bit(PG_dcache_clean, &folio->flags.f))
+		clear_bit(PG_dcache_clean, &folio->flags.f);
+}
+EXPORT_SYMBOL(flush_dcache_folio);
+
+void flush_dcache_page(struct page *page)
+{
+	flush_dcache_folio(page_folio(page));
+}
+EXPORT_SYMBOL(flush_dcache_page);
+
+/*
+ * Additional functions defined in assembly.
+ */
+EXPORT_SYMBOL(caches_clean_inval_pou);
+
+#ifdef CONFIG_ARCH_HAS_PMEM_API
+void arch_wb_cache_pmem(void *addr, size_t size)
+{
+	/* Ensure order against any prior non-cacheable writes */
+	dmb(osh);
+	dcache_clean_pop((unsigned long)addr, (unsigned long)addr + size);
+}
+EXPORT_SYMBOL_GPL(arch_wb_cache_pmem);
+
+void arch_invalidate_pmem(void *addr, size_t size)
+{
+	dcache_inval_poc((unsigned long)addr, (unsigned long)addr + size);
+}
+EXPORT_SYMBOL_GPL(arch_invalidate_pmem);
+#endif