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, 67 insertions, 0 deletions

diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
new file mode 100644
index 000000000..bf5110b91
--- /dev/null
+++ b/arch/arm64/mm/pgd.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * PGD allocation/freeing
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ */
+
+#include <linux/mm.h>
+#include <linux/gfp.h>
+#include <linux/highmem.h>
+#include <linux/slab.h>
+
+#include <asm/pgalloc.h>
+#include <asm/page.h>
+#include <asm/tlbflush.h>
+
+static struct kmem_cache *pgd_cache __ro_after_init;
+
+static bool pgdir_is_page_size(void)
+{
+	if (PGD_SIZE == PAGE_SIZE)
+		return true;
+	if (CONFIG_PGTABLE_LEVELS == 4)
+		return !pgtable_l4_enabled();
+	if (CONFIG_PGTABLE_LEVELS == 5)
+		return !pgtable_l5_enabled();
+	return false;
+}
+
+pgd_t *pgd_alloc(struct mm_struct *mm)
+{
+	gfp_t gfp = GFP_PGTABLE_USER;
+
+	if (pgdir_is_page_size())
+		return __pgd_alloc(mm, 0);
+	else
+		return kmem_cache_alloc(pgd_cache, gfp);
+}
+
+void pgd_free(struct mm_struct *mm, pgd_t *pgd)
+{
+	if (pgdir_is_page_size())
+		__pgd_free(mm, pgd);
+	else
+		kmem_cache_free(pgd_cache, pgd);
+}
+
+void __init pgtable_cache_init(void)
+{
+	if (pgdir_is_page_size())
+		return;
+
+#ifdef CONFIG_ARM64_PA_BITS_52
+	/*
+	 * With 52-bit physical addresses, the architecture requires the
+	 * top-level table to be aligned to at least 64 bytes.
+	 */
+	BUILD_BUG_ON(!IS_ALIGNED(PGD_SIZE, 64));
+#endif
+
+	/*
+	 * Naturally aligned pgds required by the architecture.
+	 */
+	pgd_cache = kmem_cache_create("pgd_cache", PGD_SIZE, PGD_SIZE,
+				      SLAB_PANIC, NULL);
+}