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, 131 insertions, 0 deletions

diff --git a/tools/testing/vma/shared.c b/tools/testing/vma/shared.c
new file mode 100644
index 000000000..2565a5aec
--- /dev/null
+++ b/tools/testing/vma/shared.c
@@ -0,0 +1,131 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "shared.h"
+
+
+bool fail_prealloc;
+unsigned long mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
+unsigned long dac_mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
+unsigned long stack_guard_gap = 256UL<<PAGE_SHIFT;
+
+const struct vm_operations_struct vma_dummy_vm_ops;
+struct anon_vma dummy_anon_vma;
+struct task_struct __current;
+
+struct vm_area_struct *alloc_vma(struct mm_struct *mm,
+		unsigned long start, unsigned long end,
+		pgoff_t pgoff, vma_flags_t vma_flags)
+{
+	struct vm_area_struct *vma = vm_area_alloc(mm);
+
+	if (vma == NULL)
+		return NULL;
+
+	vma->vm_start = start;
+	vma->vm_end = end;
+	vma->vm_pgoff = pgoff;
+	vma->flags = vma_flags;
+	vma_assert_detached(vma);
+
+	return vma;
+}
+
+void detach_free_vma(struct vm_area_struct *vma)
+{
+	vma_mark_detached(vma);
+	vm_area_free(vma);
+}
+
+struct vm_area_struct *alloc_and_link_vma(struct mm_struct *mm,
+		unsigned long start, unsigned long end,
+		pgoff_t pgoff, vma_flags_t vma_flags)
+{
+	struct vm_area_struct *vma = alloc_vma(mm, start, end, pgoff, vma_flags);
+
+	if (vma == NULL)
+		return NULL;
+
+	if (attach_vma(mm, vma)) {
+		detach_free_vma(vma);
+		return NULL;
+	}
+
+	/*
+	 * Reset this counter which we use to track whether writes have
+	 * begun. Linking to the tree will have caused this to be incremented,
+	 * which means we will get a false positive otherwise.
+	 */
+	vma->vm_lock_seq = UINT_MAX;
+
+	return vma;
+}
+
+void reset_dummy_anon_vma(void)
+{
+	dummy_anon_vma.was_cloned = false;
+	dummy_anon_vma.was_unlinked = false;
+}
+
+int cleanup_mm(struct mm_struct *mm, struct vma_iterator *vmi)
+{
+	struct vm_area_struct *vma;
+	int count = 0;
+
+	fail_prealloc = false;
+	reset_dummy_anon_vma();
+
+	vma_iter_set(vmi, 0);
+	for_each_vma(*vmi, vma) {
+		detach_free_vma(vma);
+		count++;
+	}
+
+	mtree_destroy(&mm->mm_mt);
+	mm->map_count = 0;
+	return count;
+}
+
+bool vma_write_started(struct vm_area_struct *vma)
+{
+	int seq = vma->vm_lock_seq;
+
+	/* We reset after each check. */
+	vma->vm_lock_seq = UINT_MAX;
+
+	/* The vma_start_write() stub simply increments this value. */
+	return seq > -1;
+}
+
+void __vma_set_dummy_anon_vma(struct vm_area_struct *vma,
+		struct anon_vma_chain *avc, struct anon_vma *anon_vma)
+{
+	vma->anon_vma = anon_vma;
+	INIT_LIST_HEAD(&vma->anon_vma_chain);
+	list_add(&avc->same_vma, &vma->anon_vma_chain);
+	avc->anon_vma = vma->anon_vma;
+}
+
+void vma_set_dummy_anon_vma(struct vm_area_struct *vma,
+		struct anon_vma_chain *avc)
+{
+	__vma_set_dummy_anon_vma(vma, avc, &dummy_anon_vma);
+}
+
+struct task_struct *get_current(void)
+{
+	return &__current;
+}
+
+unsigned long rlimit(unsigned int limit)
+{
+	return (unsigned long)-1;
+}
+
+void vma_set_range(struct vm_area_struct *vma,
+		   unsigned long start, unsigned long end,
+		   pgoff_t pgoff)
+{
+	vma->vm_start = start;
+	vma->vm_end = end;
+	vma->vm_pgoff = pgoff;
+}