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, 126 insertions, 0 deletions

diff --git a/arch/x86/boot/video-bios.c b/arch/x86/boot/video-bios.c
new file mode 100644
index 000000000..6eb8c06bc
--- /dev/null
+++ b/arch/x86/boot/video-bios.c
@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* -*- linux-c -*- ------------------------------------------------------- *
+ *
+ *   Copyright (C) 1991, 1992 Linus Torvalds
+ *   Copyright 2007 rPath, Inc. - All Rights Reserved
+ *   Copyright 2009 Intel Corporation; author H. Peter Anvin
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * Standard video BIOS modes
+ *
+ * We have two options for this; silent and scanned.
+ */
+
+#include "boot.h"
+#include "video.h"
+
+static __videocard video_bios;
+
+/* Set a conventional BIOS mode */
+static int set_bios_mode(u8 mode);
+
+static int bios_set_mode(struct mode_info *mi)
+{
+	return set_bios_mode(mi->mode - VIDEO_FIRST_BIOS);
+}
+
+static int set_bios_mode(u8 mode)
+{
+	struct biosregs ireg, oreg;
+	u8 new_mode;
+
+	initregs(&ireg);
+	ireg.al = mode;		/* AH=0x00 Set Video Mode */
+	intcall(0x10, &ireg, NULL);
+
+	ireg.ah = 0x0f;		/* Get Current Video Mode */
+	intcall(0x10, &ireg, &oreg);
+
+	do_restore = 1;		/* Assume video contents were lost */
+
+	/* Not all BIOSes are clean with the top bit */
+	new_mode = oreg.al & 0x7f;
+
+	if (new_mode == mode)
+		return 0;	/* Mode change OK */
+
+#ifndef _WAKEUP
+	if (new_mode != boot_params.screen_info.orig_video_mode) {
+		/* Mode setting failed, but we didn't end up where we
+		   started.  That's bad.  Try to revert to the original
+		   video mode. */
+		ireg.ax = boot_params.screen_info.orig_video_mode;
+		intcall(0x10, &ireg, NULL);
+	}
+#endif
+	return -1;
+}
+
+static int bios_probe(void)
+{
+	u8 mode;
+#ifdef _WAKEUP
+	u8 saved_mode = 0x03;
+#else
+	u8 saved_mode = boot_params.screen_info.orig_video_mode;
+#endif
+	u16 crtc;
+	struct mode_info *mi;
+	int nmodes = 0;
+
+	if (adapter != ADAPTER_EGA && adapter != ADAPTER_VGA)
+		return 0;
+
+	set_fs(0);
+	crtc = vga_crtc();
+
+	video_bios.modes = GET_HEAP(struct mode_info, 0);
+
+	for (mode = 0x14; mode <= 0x7f; mode++) {
+		if (!heap_free(sizeof(struct mode_info)))
+			break;
+
+		if (mode_defined(VIDEO_FIRST_BIOS+mode))
+			continue;
+
+		if (set_bios_mode(mode))
+			continue;
+
+		/* Try to verify that it's a text mode. */
+
+		/* Attribute Controller: make graphics controller disabled */
+		if (in_idx(0x3c0, 0x10) & 0x01)
+			continue;
+
+		/* Graphics Controller: verify Alpha addressing enabled */
+		if (in_idx(0x3ce, 0x06) & 0x01)
+			continue;
+
+		/* CRTC cursor location low should be zero(?) */
+		if (in_idx(crtc, 0x0f))
+			continue;
+
+		mi = GET_HEAP(struct mode_info, 1);
+		mi->mode = VIDEO_FIRST_BIOS+mode;
+		mi->depth = 0;	/* text */
+		mi->x = rdfs16(0x44a);
+		mi->y = rdfs8(0x484)+1;
+		nmodes++;
+	}
+
+	set_bios_mode(saved_mode);
+
+	return nmodes;
+}
+
+static __videocard video_bios =
+{
+	.card_name	= "BIOS",
+	.probe		= bios_probe,
+	.set_mode	= bios_set_mode,
+	.unsafe		= 1,
+	.xmode_first	= VIDEO_FIRST_BIOS,
+	.xmode_n	= 0x80,
+};