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, 29 insertions, 0 deletions

diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
new file mode 100644
index 000000000..b0e1423b0
--- /dev/null
+++ b/scripts/Makefile.gcc-plugins
@@ -0,0 +1,29 @@
+# SPDX-License-Identifier: GPL-2.0
+
+gcc-plugin-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)	+= latent_entropy_plugin.so
+gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)		\
+		+= -DLATENT_ENTROPY_PLUGIN
+ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
+    DISABLE_LATENT_ENTROPY_PLUGIN += -fplugin-arg-latent_entropy_plugin-disable -ULATENT_ENTROPY_PLUGIN
+endif
+export DISABLE_LATENT_ENTROPY_PLUGIN
+
+# All the plugin CFLAGS are collected here in case a build target needs to
+# filter them out of the KBUILD_CFLAGS.
+GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y)) -DGCC_PLUGINS
+export GCC_PLUGINS_CFLAGS
+
+# Add the flags to the build!
+KBUILD_CFLAGS += $(GCC_PLUGINS_CFLAGS)
+
+# Some plugins are enabled outside of this Makefile, but they still need to
+# be included in GCC_PLUGIN so they can get built.
+gcc-plugin-external-$(CONFIG_GCC_PLUGIN_RANDSTRUCT)		\
+	+= randomize_layout_plugin.so
+gcc-plugin-external-$(CONFIG_GCC_PLUGIN_STACKLEAK)		\
+	+= stackleak_plugin.so
+
+# All enabled GCC plugins are collected here for building in
+# scripts/gcc-scripts/Makefile.
+GCC_PLUGIN := $(gcc-plugin-y) $(gcc-plugin-external-y)
+export GCC_PLUGIN