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[PATCH v3 2/2] rust: add flags for shadow call stack sanitizer

Alice Ryhl posted 2 patches 1 year, 7 months ago
There is a newer version of this series
[PATCH v3 2/2] rust: add flags for shadow call stack sanitizer
Posted by Alice Ryhl 1 year, 7 months ago 
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
feature request to add this. Kconfig is not configured to reject this
configuration because that leads to cyclic Kconfig rules.

Link: https://github.com/rust-lang/rust/issues/121972 [1]
Signed-off-by: Alice Ryhl <aliceryhl@google.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
Re: [PATCH v3 2/2] rust: add flags for shadow call stack sanitizer
Posted by Conor Dooley 1 year, 7 months ago 
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
> feature request to add this. Kconfig is not configured to reject this
> configuration because that leads to cyclic Kconfig rules.
> 
> Link: https://github.com/rust-lang/rust/issues/121972 [1]
> Signed-off-by: Alice Ryhl <aliceryhl@google.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

For these security related options, like CFI_CLANG or RANDSTRUCT, I'm
inclined to say that RUST is actually what should grow the depends on.
That way it'll be RUST that gets silently disabled in configs when patch
1 gets backported (where it is mostly useless anyway) rather than SCS
nor will it disable SCS when someone enables RUST in their config,
instead it'd be a conscious choice.

Cheers,
Conor.
Re: [PATCH v3 2/2] rust: add flags for shadow call stack sanitizer
Posted by Alice Ryhl 1 year, 7 months ago 
On Thu, Jul 4, 2024 at 7:17 PM Conor Dooley <conor@kernel.org> wrote:
>
> 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
> > feature request to add this. Kconfig is not configured to reject this
> > configuration because that leads to cyclic Kconfig rules.
> >
> > Link: https://github.com/rust-lang/rust/issues/121972 [1]
> > Signed-off-by: Alice Ryhl <aliceryhl@google.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
>
> For these security related options, like CFI_CLANG or RANDSTRUCT, I'm
> inclined to say that RUST is actually what should grow the depends on.
> That way it'll be RUST that gets silently disabled in configs when patch
> 1 gets backported (where it is mostly useless anyway) rather than SCS
> nor will it disable SCS when someone enables RUST in their config,
> instead it'd be a conscious choice.

Okay, I'll make that change. I suspect this will also break the
Kconfig cycle mentioned in the commit message. Thanks for the
suggestion!

Alice
Re: [PATCH v3 2/2] rust: add flags for shadow call stack sanitizer
Posted by Sami Tolvanen 1 year, 7 months ago 
On Thu, Jul 4, 2024 at 10:17 AM Conor Dooley <conor@kernel.org> wrote:
>
> For these security related options, like CFI_CLANG or RANDSTRUCT, I'm
> inclined to say that RUST is actually what should grow the depends on.
> That way it'll be RUST that gets silently disabled in configs when patch
> 1 gets backported (where it is mostly useless anyway) rather than SCS
> nor will it disable SCS when someone enables RUST in their config,
> instead it'd be a conscious choice.

I agree, we shouldn't silently disable hardening features when Rust is enabled.

Sami
Re: [PATCH v3 2/2] rust: add flags for shadow call stack sanitizer
Posted by Alice Ryhl 1 year, 7 months ago 
On Tue, Jul 9, 2024 at 2:10 AM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> On Thu, Jul 4, 2024 at 10:17 AM Conor Dooley <conor@kernel.org> wrote:
> >
> > For these security related options, like CFI_CLANG or RANDSTRUCT, I'm
> > inclined to say that RUST is actually what should grow the depends on.
> > That way it'll be RUST that gets silently disabled in configs when patch
> > 1 gets backported (where it is mostly useless anyway) rather than SCS
> > nor will it disable SCS when someone enables RUST in their config,
> > instead it'd be a conscious choice.
>
> I agree, we shouldn't silently disable hardening features when Rust is enabled.

That definitely wasn't my intention. I'll update it for v4.

Alice
Re: [PATCH v3 2/2] rust: add flags for shadow call stack sanitizer
Posted by Nathan Chancellor 1 year, 7 months ago 
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@google.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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