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, 111 insertions, 0 deletions

diff --git a/arch/arm/mm/pageattr.c b/arch/arm/mm/pageattr.c
new file mode 100644
index 000000000..064ad508c
--- /dev/null
+++ b/arch/arm/mm/pageattr.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2014, The Linux Foundation. All rights reserved.
+ */
+#include <linux/mm.h>
+#include <linux/module.h>
+
+#include <asm/tlbflush.h>
+#include <asm/set_memory.h>
+
+struct page_change_data {
+	pgprot_t set_mask;
+	pgprot_t clear_mask;
+};
+
+static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
+{
+	struct page_change_data *cdata = data;
+	pte_t pte = *ptep;
+
+	pte = clear_pte_bit(pte, cdata->clear_mask);
+	pte = set_pte_bit(pte, cdata->set_mask);
+
+	set_pte_ext(ptep, pte, 0);
+	return 0;
+}
+
+static bool range_in_range(unsigned long start, unsigned long size,
+	unsigned long range_start, unsigned long range_end)
+{
+	return start >= range_start && start < range_end &&
+		size <= range_end - start;
+}
+
+/*
+ * This function assumes that the range is mapped with PAGE_SIZE pages.
+ */
+static int __change_memory_common(unsigned long start, unsigned long size,
+				pgprot_t set_mask, pgprot_t clear_mask)
+{
+	struct page_change_data data;
+	int ret;
+
+	data.set_mask = set_mask;
+	data.clear_mask = clear_mask;
+
+	ret = apply_to_page_range(&init_mm, start, size, change_page_range,
+				  &data);
+
+	flush_tlb_kernel_range(start, start + size);
+	return ret;
+}
+
+static int change_memory_common(unsigned long addr, int numpages,
+				pgprot_t set_mask, pgprot_t clear_mask)
+{
+	unsigned long start = addr & PAGE_MASK;
+	unsigned long end = PAGE_ALIGN(addr) + numpages * PAGE_SIZE;
+	unsigned long size = end - start;
+
+	WARN_ON_ONCE(start != addr);
+
+	if (!size)
+		return 0;
+
+	if (!range_in_range(start, size, MODULES_VADDR, MODULES_END) &&
+	    !range_in_range(start, size, VMALLOC_START, VMALLOC_END))
+		return -EINVAL;
+
+	return __change_memory_common(start, size, set_mask, clear_mask);
+}
+
+int set_memory_ro(unsigned long addr, int numpages)
+{
+	return change_memory_common(addr, numpages,
+					__pgprot(L_PTE_RDONLY),
+					__pgprot(0));
+}
+
+int set_memory_rw(unsigned long addr, int numpages)
+{
+	return change_memory_common(addr, numpages,
+					__pgprot(0),
+					__pgprot(L_PTE_RDONLY));
+}
+
+int set_memory_nx(unsigned long addr, int numpages)
+{
+	return change_memory_common(addr, numpages,
+					__pgprot(L_PTE_XN),
+					__pgprot(0));
+}
+
+int set_memory_x(unsigned long addr, int numpages)
+{
+	return change_memory_common(addr, numpages,
+					__pgprot(0),
+					__pgprot(L_PTE_XN));
+}
+
+int set_memory_valid(unsigned long addr, int numpages, int enable)
+{
+	if (enable)
+		return __change_memory_common(addr, PAGE_SIZE * numpages,
+					      __pgprot(L_PTE_VALID),
+					      __pgprot(0));
+	else
+		return __change_memory_common(addr, PAGE_SIZE * numpages,
+					      __pgprot(0),
+					      __pgprot(L_PTE_VALID));
+}