selftests/bpf: Test packet range of pointers sharing an idgrafted

Add tests where two packet pointers share an id and tightening one
pointer's umax from its var_off would put it less than their constant
distance from the other's umax: with an index & 0x38 capped at 50, the
base pointer keeps umax 50, so the pointer 8 bytes further on must keep
umax 58, even though its known bits allow at most 56.

These refused a valid program or accepted an out-of-bounds access before
the fix:

- check the advanced copy, load through the base: valid, was refused;
- check the base, load the byte at base + 1 through a copy advanced by
  8: was accepted;
- check base + 4, load 4 bytes at base + 2 through base + 8: reads two
  bytes past the checked range, was accepted;
- the same as the second with data_meta pointers checked against data:
  was accepted.

These pass with and without the fix and cover nearby paths:

- subtract an unknown scalar from a checked pointer and load below it
  (the range is kept across a new id);
- reach a load through two paths whose checks cover 8 and 7 bytes after
  the loaded pointer; the second path must not be pruned by the first;
- spill a copy of a pointer, check the pointer, fill the copy and load
  one byte past the checked range: the load is refused, and the copy
  has the range of the check.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20261001145255.855630-2-alexei.starovoitov@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/include/asm-generic/mmu_context.h b/include/asm-generic/mmu_context.h
new file mode 100644
index 000000000..91727065b
--- /dev/null
+++ b/include/asm-generic/mmu_context.h
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_GENERIC_MMU_CONTEXT_H
+#define __ASM_GENERIC_MMU_CONTEXT_H
+
+/*
+ * Generic hooks to implement no-op functionality.
+ */
+
+struct task_struct;
+struct mm_struct;
+
+/*
+ * enter_lazy_tlb - Called when "tsk" is about to enter lazy TLB mode.
+ *
+ * @mm:  the currently active mm context which is becoming lazy
+ * @tsk: task which is entering lazy tlb
+ *
+ * tsk->mm will be NULL
+ */
+#ifndef enter_lazy_tlb
+static inline void enter_lazy_tlb(struct mm_struct *mm,
+			struct task_struct *tsk)
+{
+}
+#endif
+
+/**
+ * init_new_context - Initialize context of a new mm_struct.
+ * @tsk: task struct for the mm
+ * @mm:  the new mm struct
+ * @return: 0 on success, -errno on failure
+ */
+#ifndef init_new_context
+static inline int init_new_context(struct task_struct *tsk,
+			struct mm_struct *mm)
+{
+	return 0;
+}
+#endif
+
+/**
+ * destroy_context - Undo init_new_context when the mm is going away
+ * @mm: old mm struct
+ */
+#ifndef destroy_context
+static inline void destroy_context(struct mm_struct *mm)
+{
+}
+#endif
+
+/**
+ * activate_mm - called after exec switches the current task to a new mm, to switch to it
+ * @prev_mm: previous mm of this task
+ * @next_mm: new mm
+ */
+#ifndef activate_mm
+static inline void activate_mm(struct mm_struct *prev_mm,
+			       struct mm_struct *next_mm)
+{
+	switch_mm(prev_mm, next_mm, current);
+}
+#endif
+
+/**
+ * dectivate_mm - called when an mm is released after exit or exec switches away from it
+ * @tsk: the task
+ * @mm:  the old mm
+ */
+#ifndef deactivate_mm
+static inline void deactivate_mm(struct task_struct *tsk,
+			struct mm_struct *mm)
+{
+}
+#endif
+
+#endif /* __ASM_GENERIC_MMU_CONTEXT_H */