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, 75 insertions, 0 deletions

diff --git a/arch/arm/mm/fault.h b/arch/arm/mm/fault.h
new file mode 100644
index 000000000..207f1b069
--- /dev/null
+++ b/arch/arm/mm/fault.h
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARCH_ARM_FAULT_H
+#define __ARCH_ARM_FAULT_H
+
+/*
+ * Fault status register encodings.  We steal bit 31 for our own purposes.
+ */
+#define FSR_LNX_PF		BIT(31)
+#define FSR_CM			BIT(13)
+#define FSR_WRITE		BIT(11)
+
+#ifdef CONFIG_ARM_LPAE
+#define FSR_FS_AEA		17
+#define FS_TRANS_NOLL		0x4
+#define FS_PERM_NOLL		0xC
+#define FS_MMU_NOLL_MASK	0x3C
+
+#define FSR_FS5_0		GENMASK(5, 0)
+
+static inline int fsr_fs(unsigned int fsr)
+{
+	return fsr & FSR_FS5_0;
+}
+
+static inline bool is_translation_fault(unsigned int fsr)
+{
+	int fs = fsr_fs(fsr);
+
+	return (fs & FS_MMU_NOLL_MASK) == FS_TRANS_NOLL;
+}
+
+static inline bool is_permission_fault(unsigned int fsr)
+{
+	int fs = fsr_fs(fsr);
+
+	return (fs & FS_MMU_NOLL_MASK) == FS_PERM_NOLL;
+}
+#else
+#define FSR_FS_AEA		22
+#define FS_L1_TRANS		0x5
+#define FS_L2_TRANS		0x7
+#define FS_L1_PERM		0xD
+#define FS_L2_PERM		0xF
+
+#define FSR_FS4			BIT(10)
+#define FSR_FS3_0		GENMASK(3, 0)
+
+static inline int fsr_fs(unsigned int fsr)
+{
+	return (fsr & FSR_FS3_0) | (fsr & FSR_FS4) >> 6;
+}
+
+static inline bool is_translation_fault(unsigned int fsr)
+{
+	int fs = fsr_fs(fsr);
+
+	return fs == FS_L1_TRANS || fs == FS_L2_TRANS;
+}
+
+static inline bool is_permission_fault(unsigned int fsr)
+{
+	int fs = fsr_fs(fsr);
+
+	return fs == FS_L1_PERM || fs == FS_L2_PERM;
+}
+#endif
+
+void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs);
+void early_abt_enable(void);
+asmlinkage void do_DataAbort(unsigned long addr, unsigned int fsr,
+			     struct pt_regs *regs);
+asmlinkage void do_PrefetchAbort(unsigned long addr, unsigned int ifsr,
+				 struct pt_regs *regs);
+
+#endif	/* __ARCH_ARM_FAULT_H */