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, 21 insertions, 0 deletions

diff --git a/scripts/basic/Makefile b/scripts/basic/Makefile
new file mode 100644
index 000000000..fb8e2c38f
--- /dev/null
+++ b/scripts/basic/Makefile
@@ -0,0 +1,21 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# fixdep: used to generate dependency information during build process
+
+hostprogs-always-y	+= fixdep
+
+# randstruct: the seed is needed before building the gcc-plugin or
+# before running a Clang kernel build.
+gen-randstruct-seed	:= $(srctree)/scripts/gen-randstruct-seed.sh
+quiet_cmd_create_randstruct_seed = GENSEED $@
+cmd_create_randstruct_seed = \
+	$(CONFIG_SHELL) $(gen-randstruct-seed) \
+		$@ $(objtree)/include/generated/randstruct_hash.h
+$(obj)/randstruct.seed: $(gen-randstruct-seed) FORCE
+	$(call if_changed,create_randstruct_seed)
+always-$(CONFIG_RANDSTRUCT) += randstruct.seed
+
+# integer-wrap: if the .scl file changes, we need to do a full rebuild.
+$(obj)/../../include/generated/integer-wrap.h: $(srctree)/scripts/integer-wrap-ignore.scl FORCE
+	$(call if_changed,touch)
+always-$(CONFIG_UBSAN_INTEGER_WRAP) += ../../include/generated/integer-wrap.h