[PATCH 2/2] kbuild: rust: Enable KASAN support

[Matthew Maurer]

Rust supports KASAN via LLVM, but prior to this patch, the flags aren't
set properly.

Suggested-by: Miguel Ojeda <oj...@kernel.org>
Signed-off-by: Matthew Maurer <mma...@google.com>
---
scripts/Makefile.kasan | 46 +++++++++++++++++++++++++++++++++++++++++-
scripts/Makefile.lib | 3 +++
2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 390658a2d5b7..84572c473e23 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -12,6 +12,7 @@ endif
KASAN_SHADOW_OFFSET ?= $(CONFIG_KASAN_SHADOW_OFFSET)

cc-param = $(call cc-option, -mllvm -$(1), $(call cc-option, --param $(1)))
+rustc-param = $(call rustc-option, -Cllvm-args=-$(1),)

ifdef CONFIG_KASAN_STACK
stack_enable := 1
@@ -28,6 +29,7 @@ else
endif

CFLAGS_KASAN_MINIMAL := -fsanitize=kernel-address
+RUSTFLAGS_KASAN_MINIMAL := -Zsanitizer=kernel-address -Zsanitizer-recover=kernel-address

# -fasan-shadow-offset fails without -fsanitize
CFLAGS_KASAN_SHADOW := $(call cc-option, -fsanitize=kernel-address \
@@ -36,13 +38,36 @@ CFLAGS_KASAN_SHADOW := $(call cc-option, -fsanitize=kernel-address \
-mllvm -asan-mapping-offset=$(KASAN_SHADOW_OFFSET)))

ifeq ($(strip $(CFLAGS_KASAN_SHADOW)),)
+ KASAN_SHADOW_SUPPORTED := n
+else
+ KASAN_SHADOW_SUPPORTED := y
+endif
+
+ifdef CONFIG_RUST
+ RUSTFLAGS_KASAN_SHADOW := $(call rustc-option $(RUSTFLAGS_KASAN_MINIMAL) \
+ -Cllvm-args=-asan-mapping-offset=$(KASAN_SHADOW_OFFSET))
+ ifeq ($(strip $(RUSTFLAGS_KASAN_SHADOW)),)
+ KASAN_SHADOW_SUPPORTED := n
+ endif
+endif
+
+ifeq ($(KASAN_SHADOW_SUPPORTED),y)
CFLAGS_KASAN := $(CFLAGS_KASAN_MINIMAL)
+ ifdef CONFIG_RUST
+ RUSTFLAGS_KASAN := $(RUSTFLAGS_KASAN_MINIMAL)
+ endif
else
# Now add all the compiler specific options that are valid standalone
CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \
$(call cc-param,asan-globals=1) \
$(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
$(call cc-param,asan-instrument-allocas=1)
+ ifdef CONFIG_RUST
+ RUSTFLAGS_KASAN := $(RUSTFLAGS_KASAN_SHADOW) \
+ $(call rustc-param,asan-globals=1) \
+ $(call rustc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
+ $(call rustc-param,asan-instrument-allocas=1)
+ endif
endif

CFLAGS_KASAN += $(call cc-param,asan-stack=$(stack_enable))
@@ -52,6 +77,11 @@ CFLAGS_KASAN += $(call cc-param,asan-stack=$(stack_enable))
# memintrinsics won't be checked by KASAN on GENERIC_ENTRY architectures.
CFLAGS_KASAN += $(call cc-param,asan-kernel-mem-intrinsic-prefix=1)

+ifdef CONFIG_RUST
+ RUSTFLAGS_KASAN += $(call rustc-param,asan-stack=$(stack_enable))
+ RUSTFLAGS_KASAN += $(call rustc-param,asan-kernel-mem-intrinsic-prefix=1)
+endif
+
endif # CONFIG_KASAN_GENERIC

ifdef CONFIG_KASAN_SW_TAGS
@@ -73,6 +103,20 @@ ifeq ($(call clang-min-version, 150000)$(call gcc-min-version, 130000),y)
CFLAGS_KASAN += $(call cc-param,hwasan-kernel-mem-intrinsic-prefix=1)
endif

+ifdef CONFIG_RUST
+ ifdef CONFIG_KASAN_INLINE
+ rust_instrumentation_flags := $(call rustc-param,hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET))
+ else
+ rust_instrumentation_flags := $(call rustc-param,hwasan-instrument-with-calls=1)
+ endif
+ RUSTFLAGS_KASAN := -Zsanitizer=kernel-hwaddress -Zsanitizer-recover=kernel-hwaddress \
+ $(call rustc-param,hwasan-instrument-stack=$(stack_enable)) \
+ $(call rustc-param,hwasan-use-short-granules=0) \
+ $(call rustc-param,hwasan-inline-all-checks=0) \
+ $(call rustc-param,hwasan-kernel-mem-intrinsic-prefix=1) \
+ $(instrumentation_flags)
+endif
+
endif # CONFIG_KASAN_SW_TAGS

-export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE
+export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE RUSTFLAGS_KASAN
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 9f06f6aaf7fc..4a58636705e0 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -167,6 +167,9 @@ ifneq ($(CONFIG_KASAN_HW_TAGS),y)
_c_flags += $(if $(patsubst n%,, \
$(KASAN_SANITIZE_$(target-stem).o)$(KASAN_SANITIZE)$(is-kernel-object)), \
$(CFLAGS_KASAN), $(CFLAGS_KASAN_NOSANITIZE))
+_rust_flags += $(if $(patsubst n%,, \
+ $(KASAN_SANITIZE_$(target-stem).o)$(KASAN_SANITIZE)$(is-kernel-object)), \
+ $(RUSTFLAGS_KASAN))
endif
endif

--
2.46.0.rc1.232.g9752f9e123-goog

[Andrey Konovalov]

On Fri, Jul 26, 2024 at 1:21 AM Matthew Maurer <mma...@google.com> wrote:
>
> Rust supports KASAN via LLVM, but prior to this patch, the flags aren't
> set properly.
>
> Suggested-by: Miguel Ojeda <oj...@kernel.org>
> Signed-off-by: Matthew Maurer <mma...@google.com>

Hi Matthew,

> CFLAGS_KASAN_MINIMAL := -fsanitize=kernel-address
> +RUSTFLAGS_KASAN_MINIMAL := -Zsanitizer=kernel-address -Zsanitizer-recover=kernel-address

If I recall correctly, the reason we need CFLAGS_KASAN_MINIMAL is
because older compilers don't support some of the additional options.
With Rust, this shouldn't be needed, as it requires a modern compiler
that does support all needed options. E.g., for CONFIG_KASAN_SW_TAGS,
we also don't have the MINIMAL thing for the same reason. (Possibly,
we also already don't need this for GENERIC KASAN, as the GCC version
requirement was raised a few times since KASAN was introduced.)

> # Now add all the compiler specific options that are valid standalone
> CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \
> $(call cc-param,asan-globals=1) \
> $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
> $(call cc-param,asan-instrument-allocas=1)
> + ifdef CONFIG_RUST
> + RUSTFLAGS_KASAN := $(RUSTFLAGS_KASAN_SHADOW) \
> + $(call rustc-param,asan-globals=1) \
> + $(call rustc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
> + $(call rustc-param,asan-instrument-allocas=1)

I'm wondering if there's a way to avoid duplicating all options for
Rust. Perhaps, some kind of macro?

Thanks!

[Dmitry Vyukov]

On Fri, 26 Jul 2024 at 01:57, Andrey Konovalov <andre...@gmail.com> wrote:
>
> On Fri, Jul 26, 2024 at 1:21 AM Matthew Maurer <mma...@google.com> wrote:
> >
> > Rust supports KASAN via LLVM, but prior to this patch, the flags aren't
> > set properly.

This is great, thanks, Matthew!

Does Rust support KUnit tests?
It would be good to add at least a simple positive test similar to the
existing ones so that the support does not get rotten soon.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/kasan/kasan_test.c

[Miguel Ojeda]

On Fri, Jul 26, 2024 at 12:23 PM Dmitry Vyukov <dvy...@google.com> wrote:
>
> This is great, thanks, Matthew!
>
> Does Rust support KUnit tests?
> It would be good to add at least a simple positive test similar to the
> existing ones so that the support does not get rotten soon.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/kasan/kasan_test.c

Yeah, we have Rust doctests converted into KUnit tests, as well as
upcoming `#[test]`s support (also handled as KUnit tests). For this, I
assume the latter would make more sense, but we have to merge it.

Cheers,
Miguel