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>

2 files changed, 72 insertions, 0 deletions

diff --git a/arch/x86/video/Makefile b/arch/x86/video/Makefile
new file mode 100644
index 000000000..dcfbe7a59
--- /dev/null
+++ b/arch/x86/video/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-y	+= video-common.o
diff --git a/arch/x86/video/video-common.c b/arch/x86/video/video-common.c
new file mode 100644
index 000000000..8ed82fff7
--- /dev/null
+++ b/arch/x86/video/video-common.c
@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2007 Antonino Daplas <adaplas@gmail.com>
+ *
+ * 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.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/sysfb.h>
+#include <linux/vgaarb.h>
+
+#include <asm/video.h>
+
+pgprot_t pgprot_framebuffer(pgprot_t prot,
+			    unsigned long vm_start, unsigned long vm_end,
+			    unsigned long offset)
+{
+	pgprot_val(prot) &= ~_PAGE_CACHE_MASK;
+	if (boot_cpu_data.x86 > 3)
+		pgprot_val(prot) |= cachemode2protval(_PAGE_CACHE_MODE_UC_MINUS);
+
+	return prot;
+}
+EXPORT_SYMBOL(pgprot_framebuffer);
+
+bool video_is_primary_device(struct device *dev)
+{
+#ifdef CONFIG_SCREEN_INFO
+	struct screen_info *si = &sysfb_primary_display.screen;
+	struct resource res[SCREEN_INFO_MAX_RESOURCES];
+	ssize_t i, numres;
+#endif
+	struct pci_dev *pdev;
+
+	if (!dev_is_pci(dev))
+		return false;
+
+	pdev = to_pci_dev(dev);
+
+	if (!pci_is_display(pdev))
+		return false;
+
+#ifdef CONFIG_SCREEN_INFO
+	numres = screen_info_resources(si, res, ARRAY_SIZE(res));
+	if (numres > 0) {
+		for (i = 0; i < numres; ++i) {
+			if (!(res[i].flags & IORESOURCE_MEM))
+				continue;
+
+			if (pci_find_resource(pdev, &res[i]))
+				return true;
+		}
+
+		return false;
+	}
+#endif
+
+	/*
+	 * No framebuffer was set up by the firmware/bootloader, so fall back
+	 * to the default VGA device.
+	 */
+	return pdev == vga_default_device();
+}
+EXPORT_SYMBOL(video_is_primary_device);
+
+MODULE_LICENSE("GPL");