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, 27 insertions, 0 deletions

diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
new file mode 100644
index 000000000..c729bc936
--- /dev/null
+++ b/scripts/mod/Makefile
@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS_REMOVE_empty.o += $(CC_FLAGS_LTO)
+
+hostprogs-always-y	+= modpost mk_elfconfig
+always-y		+= empty.o
+
+modpost-objs	:= modpost.o file2alias.o sumversion.o symsearch.o
+
+devicetable-offsets-file := devicetable-offsets.h
+
+$(obj)/$(devicetable-offsets-file): $(obj)/devicetable-offsets.s FORCE
+	$(call filechk,offsets,__DEVICETABLE_OFFSETS_H__)
+
+targets += $(devicetable-offsets-file) devicetable-offsets.s
+
+# dependencies on generated files need to be listed explicitly
+
+$(obj)/modpost.o $(obj)/file2alias.o $(obj)/sumversion.o $(obj)/symsearch.o: $(obj)/elfconfig.h
+$(obj)/file2alias.o: $(obj)/$(devicetable-offsets-file)
+
+quiet_cmd_elfconfig = MKELF   $@
+      cmd_elfconfig = $(obj)/mk_elfconfig < $< > $@
+
+$(obj)/elfconfig.h: $(obj)/empty.o $(obj)/mk_elfconfig FORCE
+	$(call if_changed,elfconfig)
+
+targets += elfconfig.h