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, 127 insertions, 0 deletions

diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
new file mode 100644
index 000000000..7ee8a179d
--- /dev/null
+++ b/include/asm-generic/cacheflush.h
@@ -0,0 +1,127 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_CACHEFLUSH_H
+#define _ASM_GENERIC_CACHEFLUSH_H
+
+#include <linux/instrumented.h>
+
+struct mm_struct;
+struct vm_area_struct;
+struct page;
+struct address_space;
+
+/*
+ * The cache doesn't need to be flushed when TLB entries change when
+ * the cache is mapped to physical memory, not virtual memory
+ */
+#ifndef flush_cache_all
+static inline void flush_cache_all(void)
+{
+}
+#endif
+
+#ifndef flush_cache_mm
+static inline void flush_cache_mm(struct mm_struct *mm)
+{
+}
+#endif
+
+#ifndef flush_cache_dup_mm
+static inline void flush_cache_dup_mm(struct mm_struct *mm)
+{
+}
+#endif
+
+#ifndef flush_cache_range
+static inline void flush_cache_range(struct vm_area_struct *vma,
+				     unsigned long start,
+				     unsigned long end)
+{
+}
+#endif
+
+#ifndef flush_cache_page
+static inline void flush_cache_page(struct vm_area_struct *vma,
+				    unsigned long vmaddr,
+				    unsigned long pfn)
+{
+}
+#endif
+
+#ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+static inline void flush_dcache_page(struct page *page)
+{
+}
+
+#define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 0
+#endif
+
+#ifndef flush_dcache_mmap_lock
+static inline void flush_dcache_mmap_lock(struct address_space *mapping)
+{
+}
+#endif
+
+#ifndef flush_dcache_mmap_unlock
+static inline void flush_dcache_mmap_unlock(struct address_space *mapping)
+{
+}
+#endif
+
+#ifndef flush_icache_range
+static inline void flush_icache_range(unsigned long start, unsigned long end)
+{
+}
+#endif
+
+#ifndef flush_icache_user_range
+#define flush_icache_user_range flush_icache_range
+#endif
+
+#ifndef flush_icache_user_page
+static inline void flush_icache_user_page(struct vm_area_struct *vma,
+					   struct page *page,
+					   unsigned long addr, int len)
+{
+}
+#endif
+
+#ifndef flush_cache_vmap
+static inline void flush_cache_vmap(unsigned long start, unsigned long end)
+{
+}
+#endif
+
+#ifndef flush_cache_vmap_early
+static inline void flush_cache_vmap_early(unsigned long start, unsigned long end)
+{
+}
+#endif
+
+#ifndef flush_cache_vunmap
+static inline void flush_cache_vunmap(unsigned long start, unsigned long end)
+{
+}
+#endif
+
+#ifndef copy_to_user_page
+#define copy_to_user_page(vma, page, vaddr, dst, src, len)	\
+	do { \
+		instrument_copy_to_user((void __user *)dst, src, len); \
+		memcpy(dst, src, len); \
+		flush_icache_user_page(vma, page, vaddr, len); \
+	} while (0)
+#endif
+
+
+#ifndef copy_from_user_page
+#define copy_from_user_page(vma, page, vaddr, dst, src, len)		  \
+	do {								  \
+		instrument_copy_from_user_before(dst, (void __user *)src, \
+						 len);			  \
+		memcpy(dst, src, len);					  \
+		instrument_copy_from_user_after(dst, (void __user *)src, len, \
+						0);			  \
+	} while (0)
+#endif
+
+#endif /* _ASM_GENERIC_CACHEFLUSH_H */