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, 79 insertions, 0 deletions

diff --git a/arch/mips/mm/pgtable-32.c b/arch/mips/mm/pgtable-32.c
new file mode 100644
index 000000000..e2cf2166d
--- /dev/null
+++ b/arch/mips/mm/pgtable-32.c
@@ -0,0 +1,79 @@
+/*
+ * 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.
+ *
+ * Copyright (C) 2003 by Ralf Baechle
+ */
+#include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/memblock.h>
+#include <linux/highmem.h>
+#include <asm/fixmap.h>
+#include <asm/pgalloc.h>
+#include <asm/tlbflush.h>
+
+void pgd_init(void *addr)
+{
+	unsigned long *p = (unsigned long *)addr;
+	int i;
+
+	for (i = 0; i < USER_PTRS_PER_PGD; i+=8) {
+		p[i + 0] = (unsigned long) invalid_pte_table;
+		p[i + 1] = (unsigned long) invalid_pte_table;
+		p[i + 2] = (unsigned long) invalid_pte_table;
+		p[i + 3] = (unsigned long) invalid_pte_table;
+		p[i + 4] = (unsigned long) invalid_pte_table;
+		p[i + 5] = (unsigned long) invalid_pte_table;
+		p[i + 6] = (unsigned long) invalid_pte_table;
+		p[i + 7] = (unsigned long) invalid_pte_table;
+	}
+}
+
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE)
+void set_pmd_at(struct mm_struct *mm, unsigned long addr,
+		pmd_t *pmdp, pmd_t pmd)
+{
+	*pmdp = pmd;
+}
+#endif /* defined(CONFIG_TRANSPARENT_HUGEPAGE) */
+
+void __init pagetable_init(void)
+{
+	unsigned long vaddr;
+	pgd_t *pgd_base;
+#ifdef CONFIG_HIGHMEM
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+#endif
+
+	/* Initialize the entire pgd.  */
+	pgd_init(swapper_pg_dir);
+	pgd_init(&swapper_pg_dir[USER_PTRS_PER_PGD]);
+
+	pgd_base = swapper_pg_dir;
+
+	/*
+	 * Fixed mappings:
+	 */
+	vaddr = __fix_to_virt(__end_of_fixed_addresses - 1);
+	fixrange_init(vaddr & PMD_MASK, vaddr + FIXADDR_SIZE, pgd_base);
+
+#ifdef CONFIG_HIGHMEM
+	/*
+	 * Permanent kmaps:
+	 */
+	vaddr = PKMAP_BASE;
+	fixrange_init(vaddr & PMD_MASK, vaddr + PAGE_SIZE*LAST_PKMAP, pgd_base);
+
+	pgd = swapper_pg_dir + pgd_index(vaddr);
+	p4d = p4d_offset(pgd, vaddr);
+	pud = pud_offset(p4d, vaddr);
+	pmd = pmd_offset(pud, vaddr);
+	pte = pte_offset_kernel(pmd, vaddr);
+	pkmap_page_table = pte;
+#endif
+}