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, 65 insertions, 0 deletions

diff --git a/arch/mips/vdso/elf.S b/arch/mips/vdso/elf.S
new file mode 100644
index 000000000..821fcffe7
--- /dev/null
+++ b/arch/mips/vdso/elf.S
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2015 Imagination Technologies
+ * Author: Alex Smith <alex.smith@imgtec.com>
+ */
+
+#include <asm/vdso/vdso.h>
+
+#include <asm/isa-rev.h>
+
+#include <linux/build-salt.h>
+#include <linux/elfnote.h>
+#include <linux/version.h>
+
+ELFNOTE_START(Linux, 0, "a")
+	.long LINUX_VERSION_CODE
+ELFNOTE_END
+
+BUILD_SALT
+
+/*
+ * The .MIPS.abiflags section must be defined with the FP ABI flags set
+ * to 'any' to be able to link with both old and new libraries.
+ * Newer toolchains are capable of automatically generating this, but we want
+ * to work with older toolchains as well. Therefore, we define the contents of
+ * this section here (under different names), and then genvdso will patch
+ * it to have the correct name and type.
+ *
+ * We base the .MIPS.abiflags section on preprocessor definitions rather than
+ * CONFIG_* because we need to match the particular ABI we are building the
+ * VDSO for.
+ *
+ * See https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking
+ * for the .MIPS.abiflags section description.
+ */
+
+	.section .mips_abiflags, "a"
+	.align 3
+__mips_abiflags:
+	.hword	0		/* version */
+	.byte	__mips		/* isa_level */
+
+	/* isa_rev */
+	.byte	MIPS_ISA_REV
+
+	/* gpr_size */
+#ifdef __mips64
+	.byte	2		/* AFL_REG_64 */
+#else
+	.byte	1		/* AFL_REG_32 */
+#endif
+
+	/* cpr1_size */
+#if (MIPS_ISA_REV >= 6) || defined(__mips64)
+	.byte	2		/* AFL_REG_64 */
+#else
+	.byte	1		/* AFL_REG_32 */
+#endif
+
+	.byte	0		/* cpr2_size (AFL_REG_NONE) */
+	.byte	0		/* fp_abi (Val_GNU_MIPS_ABI_FP_ANY) */
+	.word	0		/* isa_ext */
+	.word	0		/* ases */
+	.word	0		/* flags1 */
+	.word	0		/* flags2 */