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, 107 insertions, 0 deletions

diff --git a/include/drm/task_barrier.h b/include/drm/task_barrier.h
new file mode 100644
index 000000000..f6e6ed529
--- /dev/null
+++ b/include/drm/task_barrier.h
@@ -0,0 +1,107 @@
+/*
+ * Copyright 2019 Advanced Micro Devices, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+#include <linux/semaphore.h>
+#include <linux/atomic.h>
+
+/*
+ * Reusable 2 PHASE task barrier (rendez-vous point) implementation for N tasks.
+ * Based on the Little book of semaphores - https://greenteapress.com/wp/semaphores/
+ */
+
+
+
+#ifndef DRM_TASK_BARRIER_H_
+#define DRM_TASK_BARRIER_H_
+
+/*
+ * Represents an instance of a task barrier.
+ */
+struct task_barrier {
+	unsigned int n;
+	atomic_t count;
+	struct semaphore enter_turnstile;
+	struct semaphore exit_turnstile;
+};
+
+static inline void task_barrier_signal_turnstile(struct semaphore *turnstile,
+						 unsigned int n)
+{
+	int i;
+
+	for (i = 0 ; i < n; i++)
+		up(turnstile);
+}
+
+static inline void task_barrier_init(struct task_barrier *tb)
+{
+	tb->n = 0;
+	atomic_set(&tb->count, 0);
+	sema_init(&tb->enter_turnstile, 0);
+	sema_init(&tb->exit_turnstile, 0);
+}
+
+static inline void task_barrier_add_task(struct task_barrier *tb)
+{
+	tb->n++;
+}
+
+static inline void task_barrier_rem_task(struct task_barrier *tb)
+{
+	tb->n--;
+}
+
+/*
+ * Lines up all the threads BEFORE the critical point.
+ *
+ * When all thread passed this code the entry barrier is back to locked state.
+ */
+static inline void task_barrier_enter(struct task_barrier *tb)
+{
+	if (atomic_inc_return(&tb->count) == tb->n)
+		task_barrier_signal_turnstile(&tb->enter_turnstile, tb->n);
+
+	down(&tb->enter_turnstile);
+}
+
+/*
+ * Lines up all the threads AFTER the critical point.
+ *
+ * This function is used to avoid any one thread running ahead if the barrier is
+ *  used repeatedly .
+ */
+static inline void task_barrier_exit(struct task_barrier *tb)
+{
+	if (atomic_dec_return(&tb->count) == 0)
+		task_barrier_signal_turnstile(&tb->exit_turnstile, tb->n);
+
+	down(&tb->exit_turnstile);
+}
+
+/* Convinieince function when nothing to be done in between entry and exit */
+static inline void task_barrier_full(struct task_barrier *tb)
+{
+	task_barrier_enter(tb);
+	task_barrier_exit(tb);
+}
+
+#endif