selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 46 insertions, 0 deletions

diff --git a/include/asm-generic/fprobe.h b/include/asm-generic/fprobe.h
new file mode 100644
index 000000000..8659a4dc6
--- /dev/null
+++ b/include/asm-generic/fprobe.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Generic arch dependent fprobe macros.
+ */
+#ifndef __ASM_GENERIC_FPROBE_H__
+#define __ASM_GENERIC_FPROBE_H__
+
+#include <linux/bits.h>
+
+#ifdef CONFIG_64BIT
+/*
+ * Encoding the size and the address of fprobe into one 64bit entry.
+ * The 32bit architectures should use 2 entries to store those info.
+ */
+
+#define ARCH_DEFINE_ENCODE_FPROBE_HEADER
+
+#define FPROBE_HEADER_MSB_SIZE_SHIFT (BITS_PER_LONG - FPROBE_DATA_SIZE_BITS)
+#define FPROBE_HEADER_MSB_MASK					\
+	GENMASK(FPROBE_HEADER_MSB_SIZE_SHIFT - 1, 0)
+
+/*
+ * By default, this expects the MSBs in the address of kprobe is 0xf.
+ * If any arch needs another fixed pattern (e.g. s390 is zero filled),
+ * override this.
+ */
+#define FPROBE_HEADER_MSB_PATTERN				\
+	GENMASK(BITS_PER_LONG - 1, FPROBE_HEADER_MSB_SIZE_SHIFT)
+
+#define arch_fprobe_header_encodable(fp)			\
+	(((unsigned long)(fp) & ~FPROBE_HEADER_MSB_MASK) ==	\
+	 FPROBE_HEADER_MSB_PATTERN)
+
+#define arch_encode_fprobe_header(fp, size)			\
+	(((unsigned long)(fp) & FPROBE_HEADER_MSB_MASK) |	\
+	 ((unsigned long)(size) << FPROBE_HEADER_MSB_SIZE_SHIFT))
+
+#define arch_decode_fprobe_header_size(val)			\
+	((unsigned long)(val) >> FPROBE_HEADER_MSB_SIZE_SHIFT)
+
+#define arch_decode_fprobe_header_fp(val)					\
+	((struct fprobe *)(((unsigned long)(val) & FPROBE_HEADER_MSB_MASK) |	\
+			   FPROBE_HEADER_MSB_PATTERN))
+#endif /* CONFIG_64BIT */
+
+#endif /* __ASM_GENERIC_FPROBE_H__ */