[PATCH v2 3/3] kasan: rust: Add KASAN smoke test via UAF

[Matthew Maurer <mmaurer@google.com>]

Adds a smoke test to ensure that KASAN in Rust is actually detecting a
Rust-native UAF. There is significant room to expand this test suite,
but this will at least ensure that flags are having the intended effect.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 mm/kasan/Makefile                         |  9 ++++++++-
 mm/kasan/{kasan_test.c => kasan_test_c.c} | 13 +++++++++++++
 mm/kasan/kasan_test_rust.rs               | 17 +++++++++++++++++
 3 files changed, 38 insertions(+), 1 deletion(-)
 rename mm/kasan/{kasan_test.c => kasan_test_c.c} (99%)
 create mode 100644 mm/kasan/kasan_test_rust.rs

diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
index 7634dd2a6128..d718b0f72009 100644
--- a/mm/kasan/Makefile
+++ b/mm/kasan/Makefile
@@ -44,7 +44,8 @@ ifndef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
 CFLAGS_KASAN_TEST += -fno-builtin
 endif
 
-CFLAGS_kasan_test.o := $(CFLAGS_KASAN_TEST)
+CFLAGS_kasan_test_c.o := $(CFLAGS_KASAN_TEST)
+RUSTFLAGS_kasan_test_rust.o := $(RUSTFLAGS_KASAN)
 CFLAGS_kasan_test_module.o := $(CFLAGS_KASAN_TEST)
 
 obj-y := common.o report.o
@@ -54,3 +55,9 @@ obj-$(CONFIG_KASAN_SW_TAGS) += init.o report_sw_tags.o shadow.o sw_tags.o tags.o
 
 obj-$(CONFIG_KASAN_KUNIT_TEST) += kasan_test.o
 obj-$(CONFIG_KASAN_MODULE_TEST) += kasan_test_module.o
+
+kasan_test-objs := kasan_test_c.o
+
+ifdef CONFIG_RUST
+kasan_test-objs += kasan_test_rust.o
+endif
diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test_c.c
similarity index 99%
rename from mm/kasan/kasan_test.c
rename to mm/kasan/kasan_test_c.c
index 7b32be2a3cf0..28821c90840e 100644
--- a/mm/kasan/kasan_test.c
+++ b/mm/kasan/kasan_test_c.c
@@ -30,6 +30,7 @@
 #include <asm/page.h>
 
 #include "kasan.h"
+#include "kasan_test_rust.h"
 
 #define OOB_TAG_OFF (IS_ENABLED(CONFIG_KASAN_GENERIC) ? 0 : KASAN_GRANULE_SIZE)
 
@@ -1899,6 +1900,17 @@ static void match_all_mem_tag(struct kunit *test)
 	kfree(ptr);
 }
 
+/*
+ * Check that Rust performing a uaf using `unsafe` is detected.
+ * This is an undirected smoke test to make sure that Rust is being sanitized
+ * appropriately.
+ */
+static void rust_uaf(struct kunit *test)
+{
+	KUNIT_EXPECT_KASAN_FAIL(test, kasan_test_rust_uaf());
+}
+
+
 static struct kunit_case kasan_kunit_test_cases[] = {
 	KUNIT_CASE(kmalloc_oob_right),
 	KUNIT_CASE(kmalloc_oob_left),
@@ -1971,6 +1983,7 @@ static struct kunit_case kasan_kunit_test_cases[] = {
 	KUNIT_CASE(match_all_not_assigned),
 	KUNIT_CASE(match_all_ptr_tag),
 	KUNIT_CASE(match_all_mem_tag),
+	KUNIT_CASE(rust_uaf),
 	{}
 };
 
diff --git a/mm/kasan/kasan_test_rust.rs b/mm/kasan/kasan_test_rust.rs
new file mode 100644
index 000000000000..6f4b43ea488c
--- /dev/null
+++ b/mm/kasan/kasan_test_rust.rs
@@ -0,0 +1,17 @@
+//! Helper crate for KASAN testing
+//! Provides behavior to check the sanitization of Rust code.
+use kernel::prelude::*;
+use core::ptr::addr_of_mut;
+
+/// Trivial UAF - allocate a big vector, grab a pointer partway through,
+/// drop the vector, and touch it.
+#[no_mangle]
+pub extern "C" fn kasan_test_rust_uaf() -> u8 {
+    let mut v: Vec<u8> = Vec::new();
+    for _ in 0..4096 {
+        v.push(0x42, GFP_KERNEL).unwrap();
+    }
+    let ptr: *mut u8 = addr_of_mut!(v[2048]);
+    drop(v);
+    unsafe { *ptr }
+}
-- 
2.46.0.76.ge559c4bf1a-goog