[RFC,17/17] arm64: compile the kernel with ptrauth -msign-return-address

Commit Message

Kristina Martsenko Oct. 5, 2018, 8:47 a.m. UTC

Compile all functions with two ptrauth instructions: paciasp in the
prologue to sign the return address, and autiasp in the epilogue to
authenticate the return address. This should help protect the kernel
against attacks using return-oriented programming.

CONFIG_ARM64_PTR_AUTH enables pointer auth for both userspace and the
kernel.

Signed-off-by: Mark Rutland <[e-mail]>
Signed-off-by: Kristina Martsenko <[e-mail]>
---
 arch/arm64/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Vladimir Murzin Oct. 11, 2018, 2:23 p.m. UTC | #1

Hi Kristina,

On 05/10/18 09:47, Kristina Martsenko wrote:
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 106039d25e2f..dbcd43ea99d8 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -56,6 +56,10 @@ KBUILD_AFLAGS	+= $(lseinstr) $(brokengasinst)
>  KBUILD_CFLAGS	+= $(call cc-option,-mabi=lp64)
>  KBUILD_AFLAGS	+= $(call cc-option,-mabi=lp64)
>  
> +ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
> +KBUILD_CFLAGS	+= -msign-return-address=all
> +endif

Should not it be done via cc-option so old toolchains keep working [1]?

[1]
$ aarch64-linux-gnu-gcc --version
aarch64-linux-gnu-gcc (Linaro GCC 2014.11) 4.9.3 20141031 (prerelease)
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ aarch64-linux-gnu-gcc -msign-return-address=all
aarch64-linux-gnu-gcc: error: unrecognized command line option '-msign-return-address=all'
...

Cheers
Vladimir

Kees Cook Oct. 15, 2018, 10:38 p.m. UTC | #2

On Thu, Oct 11, 2018 at 7:23 AM, Vladimir Murzin
<[e-mail]> wrote:
> Hi Kristina,
>
> On 05/10/18 09:47, Kristina Martsenko wrote:
>> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
>> index 106039d25e2f..dbcd43ea99d8 100644
>> --- a/arch/arm64/Makefile
>> +++ b/arch/arm64/Makefile
>> @@ -56,6 +56,10 @@ KBUILD_AFLAGS      += $(lseinstr) $(brokengasinst)
>>  KBUILD_CFLAGS        += $(call cc-option,-mabi=lp64)
>>  KBUILD_AFLAGS        += $(call cc-option,-mabi=lp64)
>>
>> +ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
>> +KBUILD_CFLAGS        += -msign-return-address=all
>> +endif
>
> Should not it be done via cc-option so old toolchains keep working [1]?
>
> [1]
> $ aarch64-linux-gnu-gcc --version
> aarch64-linux-gnu-gcc (Linaro GCC 2014.11) 4.9.3 20141031 (prerelease)
> Copyright (C) 2014 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>
> $ aarch64-linux-gnu-gcc -msign-return-address=all
> aarch64-linux-gnu-gcc: error: unrecognized command line option '-msign-return-address=all'
> ...

I would like to see CONFIG_ARM64_PTR_AUTH testing for compiler support
via Kconfig (as stack-protector does). This would allow developers to
only see the option if it was available (i.e. no "downgrade" happens
if the compiler is missing support). Using cc-option runs the risk of
building a kernel with CONFIG_ARM64_PTR_AUTH set, but _not_ actually
using ptr auth.

-Kees

Patch

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 106039d25e2f..dbcd43ea99d8 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -56,6 +56,10 @@  KBUILD_AFLAGS	+= $(lseinstr) $(brokengasinst)
 KBUILD_CFLAGS	+= $(call cc-option,-mabi=lp64)
 KBUILD_AFLAGS	+= $(call cc-option,-mabi=lp64)
 
+ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
+KBUILD_CFLAGS	+= -msign-return-address=all
+endif
+
 ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
 KBUILD_CPPFLAGS	+= -mbig-endian
 CHECKFLAGS	+= -D__AARCH64EB__