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, 101 insertions, 0 deletions

diff --git a/arch/arm/lib/csumpartialcopyuser.S b/arch/arm/lib/csumpartialcopyuser.S
new file mode 100644
index 000000000..c289bde04
--- /dev/null
+++ b/arch/arm/lib/csumpartialcopyuser.S
@@ -0,0 +1,101 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/arch/arm/lib/csumpartialcopyuser.S
+ *
+ *  Copyright (C) 1995-1998 Russell King
+ *
+ * 27/03/03 Ian Molton Clean up CONFIG_CPU
+ */
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+#include <asm/errno.h>
+#include <asm/asm-offsets.h>
+
+		.text
+
+#if defined(CONFIG_CPU_SW_DOMAIN_PAN)
+
+		.macro	save_regs
+		mrc	p15, 0, ip, c3, c0, 0
+		stmfd	sp!, {r1, r2, r4 - r8, ip, lr}
+		uaccess_enable ip
+		.endm
+
+		.macro	load_regs
+		ldmfd	sp!, {r1, r2, r4 - r8, ip, lr}
+		mcr	p15, 0, ip, c3, c0, 0
+		ret	lr
+		.endm
+
+#elif defined(CONFIG_CPU_TTBR0_PAN)
+
+		.macro	save_regs
+		mrc	p15, 0, ip, c2, c0, 2		@ read TTBCR
+		stmfd	sp!, {r1, r2, r4 - r8, ip, lr}
+		uaccess_enable ip
+		.endm
+
+		.macro	load_regs
+		ldmfd	sp!, {r1, r2, r4 - r8, ip, lr}
+		mcr	p15, 0, ip, c2, c0, 2		@ restore TTBCR
+		ret	lr
+		.endm
+
+#else
+
+		.macro	save_regs
+		stmfd	sp!, {r1, r2, r4 - r8, lr}
+		.endm
+
+		.macro	load_regs
+		ldmfd	sp!, {r1, r2, r4 - r8, pc}
+		.endm
+
+#endif
+
+		.macro	load1b,	reg1
+		ldrusr	\reg1, r0, 1
+		.endm
+
+		.macro	load2b, reg1, reg2
+		ldrusr	\reg1, r0, 1
+		ldrusr	\reg2, r0, 1
+		.endm
+
+		.macro	load1l, reg1
+		ldrusr	\reg1, r0, 4
+		.endm
+
+		.macro	load2l, reg1, reg2
+		ldrusr	\reg1, r0, 4
+		ldrusr	\reg2, r0, 4
+		.endm
+
+		.macro	load4l, reg1, reg2, reg3, reg4
+		ldrusr	\reg1, r0, 4
+		ldrusr	\reg2, r0, 4
+		ldrusr	\reg3, r0, 4
+		ldrusr	\reg4, r0, 4
+		.endm
+
+/*
+ * unsigned int
+ * csum_partial_copy_from_user(const char *src, char *dst, int len)
+ *  r0 = src, r1 = dst, r2 = len
+ *  Returns : r0 = checksum or 0
+ */
+
+#define FN_ENTRY	ENTRY(csum_partial_copy_from_user)
+#define FN_EXIT		ENDPROC(csum_partial_copy_from_user)
+
+#include "csumpartialcopygeneric.S"
+
+/*
+ * We report fault by returning 0 csum - impossible in normal case, since
+ * we start with 0xffffffff for initial sum.
+ */
+		.pushsection .text.fixup,"ax"
+		.align	4
+9001:		mov	r0, #0
+		load_regs
+		.popsection