Re: [PATCH v4 4/4] kasan: rust: Add KASAN smoke test via UAF

[Andrey Konovalov]

On Tue, Aug 20, 2024 at 9:49 PM Matthew Maurer <mmaurer@xxxxxxxxxx> wrote:
>
> 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.
>
> The rename from kasan_test.c to kasan_test_c.c is in order to allow the
> single kasan_test.ko test suite to contain both a .o file produced
> by the C compiler and one produced by rustc.
>
> Signed-off-by: Matthew Maurer <mmaurer@xxxxxxxxxx>
> ---
>  mm/kasan/Makefile                         |  7 ++++++-
>  mm/kasan/kasan.h                          |  6 ++++++
>  mm/kasan/{kasan_test.c => kasan_test_c.c} | 12 ++++++++++++
>  mm/kasan/kasan_test_rust.rs               | 19 +++++++++++++++++++
>  4 files changed, 43 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..13059d9ee13c 100644
> --- a/mm/kasan/Makefile
> +++ b/mm/kasan/Makefile
> @@ -44,13 +44,18 @@ 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 := $(CFLAGS_KASAN_TEST)
>
>  obj-y := common.o report.o
>  obj-$(CONFIG_KASAN_GENERIC) += init.o generic.o report_generic.o shadow.o quarantine.o
>  obj-$(CONFIG_KASAN_HW_TAGS) += hw_tags.o report_hw_tags.o tags.o report_tags.o
>  obj-$(CONFIG_KASAN_SW_TAGS) += init.o report_sw_tags.o shadow.o sw_tags.o tags.o report_tags.o

Nit: empty line here.

> +kasan_test-objs := kasan_test_c.o
> +ifdef CONFIG_RUST
> +       kasan_test-objs += kasan_test_rust.o
> +endif
>
>  obj-$(CONFIG_KASAN_KUNIT_TEST) += kasan_test.o
>  obj-$(CONFIG_KASAN_MODULE_TEST) += kasan_test_module.o
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index fb2b9ac0659a..f438a6cdc964 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -555,6 +555,12 @@ static inline bool kasan_arch_is_ready(void)       { return true; }
>  void kasan_kunit_test_suite_start(void);
>  void kasan_kunit_test_suite_end(void);
>
> +#ifdef CONFIG_RUST
> +char kasan_test_rust_uaf(void);
> +#else
> +static inline char kasan_test_rust_uaf(void) { return '\0'; }
> +#endif
> +
>  #else /* CONFIG_KASAN_KUNIT_TEST */
>
>  static inline void kasan_kunit_test_suite_start(void) { }
> 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..dd3d2a1e3145 100644
> --- a/mm/kasan/kasan_test.c
> +++ b/mm/kasan/kasan_test_c.c
> @@ -1899,6 +1899,17 @@ static void match_all_mem_tag(struct kunit *test)
>         kfree(ptr);
>  }
>
> +/*
> + * Check that Rust performing a use-after-free using `unsafe` is detected.
> + * This is a smoke test to make sure that Rust is being sanitized properly.
> + */
> +static void rust_uaf(struct kunit *test)
> +{
> +       KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_RUST);
> +       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 +1982,7 @@ 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..7239303b232c
> --- /dev/null
> +++ b/mm/kasan/kasan_test_rust.rs
> @@ -0,0 +1,19 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! 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 }
> +}
> --
> 2.46.0.184.g6999bdac58-goog
>