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Message-ID: <20240704163908.GA1394865@thelio-3990X>
Date: Thu, 4 Jul 2024 09:39:08 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Jamie Cunliffe <Jamie.Cunliffe@....com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Masahiro Yamada <masahiroy@...nel.org>,
Nicolas Schier <nicolas@...sle.eu>,
Ard Biesheuvel <ardb@...nel.org>, Marc Zyngier <maz@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Mark Brown <broonie@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Kees Cook <keescook@...omium.org>, Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
Andreas Hindborg <a.hindborg@...sung.com>,
Valentin Obst <kernel@...entinobst.de>,
linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3 2/2] rust: add flags for shadow call stack sanitizer
Hi Alice,
On Thu, Jul 04, 2024 at 03:07:58PM +0000, Alice Ryhl wrote:
> As of rustc 1.80.0, the Rust compiler supports the -Zfixed-x18 flag, so
> we can now use Rust with the shadow call stack sanitizer.
>
> On older versions of Rust, it is possible to use shadow call stack by
> passing -Ctarget-feature=+reserve-x18 instead of -Zfixed-x18. However,
> this flag emits a warning, so this patch does not add support for that.
>
> Currently, the compiler thinks that the aarch64-unknown-none target
> doesn't support -Zsanitizer=shadow-call-stack, so the build will fail if
> you enable shadow call stack in non-dynamic mode. See [2] for the
^ this should be [1]?
> feature request to add this. Kconfig is not configured to reject this
> configuration because that leads to cyclic Kconfig rules.
While it probably does not matter much given Rust for Linux is still "in
the works", I think it would be good to avoid these build failures.
Perhaps something like this could work (which basically just forces on
UNWIND_PATCH_PAC_INTO_SCS when Rust is enabled).
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 5d91259ee7b5..a9f08a2bd1c6 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -89,7 +89,7 @@ config ARM64
select ARCH_SUPPORTS_DEBUG_PAGEALLOC
select ARCH_SUPPORTS_HUGETLBFS
select ARCH_SUPPORTS_MEMORY_FAILURE
- select ARCH_SUPPORTS_SHADOW_CALL_STACK if CC_HAVE_SHADOW_CALL_STACK
+ select ARCH_SUPPORTS_SHADOW_CALL_STACK if CC_HAVE_SHADOW_CALL_STACK && (!RUST || CAN_UNWIND_PATCH_PAC_INTO_SCS)
select ARCH_SUPPORTS_LTO_CLANG if CPU_LITTLE_ENDIAN
select ARCH_SUPPORTS_LTO_CLANG_THIN
select ARCH_SUPPORTS_CFI_CLANG
@@ -2262,12 +2262,16 @@ config STACKPROTECTOR_PER_TASK
def_bool y
depends on STACKPROTECTOR && CC_HAVE_STACKPROTECTOR_SYSREG
-config UNWIND_PATCH_PAC_INTO_SCS
- bool "Enable shadow call stack dynamically using code patching"
+config CAN_UNWIND_PATCH_PAC_INTO_SCS
+ def_bool y
# needs Clang with https://github.com/llvm/llvm-project/commit/de07cde67b5d205d58690be012106022aea6d2b3 incorporated
depends on CC_IS_CLANG && CLANG_VERSION >= 150000
depends on ARM64_PTR_AUTH_KERNEL && CC_HAS_BRANCH_PROT_PAC_RET
- depends on SHADOW_CALL_STACK
+
+config UNWIND_PATCH_PAC_INTO_SCS
+ bool "Enable shadow call stack dynamically using code patching" if !RUST
+ depends on SHADOW_CALL_STACK && CAN_UNWIND_PATCH_PAC_INTO_SCS
+ default y if RUST
select UNWIND_TABLES
select DYNAMIC_SCS
Otherwise, it might be good to wait to enable this until [1] is
addressed, but I don't really feel that strongly about it.
>From a Kconfig/Kbuild perspective, the rest of the patch seems fine.
> Link: https://github.com/rust-lang/rust/issues/121972 [1]
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> Makefile | 1 +
> arch/Kconfig | 2 +-
> arch/arm64/Makefile | 3 +++
> 3 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index c11a10c8e710..4ae741601a1c 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -945,6 +945,7 @@ ifdef CONFIG_SHADOW_CALL_STACK
> ifndef CONFIG_DYNAMIC_SCS
> CC_FLAGS_SCS := -fsanitize=shadow-call-stack
> KBUILD_CFLAGS += $(CC_FLAGS_SCS)
> +KBUILD_RUSTFLAGS += -Zsanitizer=shadow-call-stack
> endif
> export CC_FLAGS_SCS
> endif
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 238448a9cb71..5a6e296df5e6 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -690,7 +690,7 @@ config SHADOW_CALL_STACK
> bool "Shadow Call Stack"
> depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
> depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
> - depends on !RUST
> + depends on !RUST || RUSTC_VERSION >= 108000
> depends on MMU
> help
> This option enables the compiler's Shadow Call Stack, which
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 3f0f35fd5bb7..bbf313ddd700 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -57,9 +57,11 @@ KBUILD_AFLAGS += $(call cc-option,-mabi=lp64)
> ifneq ($(CONFIG_UNWIND_TABLES),y)
> KBUILD_CFLAGS += -fno-asynchronous-unwind-tables -fno-unwind-tables
> KBUILD_AFLAGS += -fno-asynchronous-unwind-tables -fno-unwind-tables
> +KBUILD_RUSTFLAGS += -Cforce-unwind-tables=n
> else
> KBUILD_CFLAGS += -fasynchronous-unwind-tables
> KBUILD_AFLAGS += -fasynchronous-unwind-tables
> +KBUILD_RUSTFLAGS += -Cforce-unwind-tables=y -Zuse-sync-unwind=n
> endif
>
> ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y)
> @@ -114,6 +116,7 @@ endif
>
> ifeq ($(CONFIG_SHADOW_CALL_STACK), y)
> KBUILD_CFLAGS += -ffixed-x18
> +KBUILD_RUSTFLAGS += -Zfixed-x18
> endif
>
> ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
>
> --
> 2.45.2.803.g4e1b14247a-goog
>
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