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, 32 insertions, 0 deletions

diff --git a/scripts/makelst b/scripts/makelst
new file mode 100755
index 000000000..e432af073
--- /dev/null
+++ b/scripts/makelst
@@ -0,0 +1,32 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# A script to dump mixed source code & assembly
+# with correct relocations from System.map
+# Requires the following lines in makefile:
+#%.lst: %.c
+#	$(CC) $(c_flags) -g -c -o $*.o $< &&
+#	$(srctree)/scripts/makelst $*.o System.map $(OBJDUMP) > $@
+#
+# Copyright (C) 2000 IBM Corporation
+# Author(s): DJ Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com)
+#            William Stearns <wstearns@pobox.com>
+#
+
+# awk style field access
+field() {
+  shift $1 ; echo $1
+}
+
+t1=`$3 --syms $1 | grep .text | grep -m1 " F "`
+if [ -n "$t1" ]; then
+  t2=`field 6 $t1`
+  if [ ! -r $2 ]; then
+    echo "No System.map" >&2
+  else
+    t3=`grep $t2 $2`
+    t4=`field 1 $t3`
+    t5=`field 1 $t1`
+    t6=`printf "%lu" $((0x$t4 - 0x$t5))`
+  fi
+fi
+$3 -r --source --adjust-vma=${t6:-0} $1