* Re: [PATCH] arm64: Always force a branch protection mode when the compiler has one
2020-03-31 19:44 [PATCH] arm64: Always force a branch protection mode when the compiler has one Mark Brown
@ 2020-03-31 19:46 ` Kees Cook
2020-04-01 9:55 ` Mark Rutland
2020-04-01 17:54 ` Catalin Marinas
2 siblings, 0 replies; 5+ messages in thread
From: Kees Cook @ 2020-03-31 19:46 UTC (permalink / raw)
To: Mark Brown
Cc: Mark Rutland, Szabolcs Nagy, Catalin Marinas, stable,
Amit Daniel Kachhap, Will Deacon, linux-arm-kernel
On Tue, Mar 31, 2020 at 08:44:59PM +0100, Mark Brown wrote:
> Compilers with branch protection support can be configured to enable it by
> default, it is likely that distributions will do this as part of deploying
> branch protection system wide. As well as the slight overhead from having
> some extra NOPs for unused branch protection features this can cause more
> serious problems when the kernel is providing pointer authentication to
> userspace but not built for pointer authentication itself. In that case our
> switching of keys for userspace can affect the kernel unexpectedly, causing
> pointer authentication instructions in the kernel to corrupt addresses.
>
> To ensure that we get consistent and reliable behaviour always explicitly
> initialise the branch protection mode, ensuring that the kernel is built
> the same way regardless of the compiler defaults.
>
> Fixes: 7503197562567 (arm64: add basic pointer authentication support)
> Reported-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
> Cc: stable@vger.kernel.org
> ---
> arch/arm64/Kconfig | 4 ++++
> arch/arm64/Makefile | 7 ++++++-
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index d3efdc095a17..1e46746e8392 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1537,6 +1537,10 @@ config ARM64_PTR_AUTH
> This feature works with FUNCTION_GRAPH_TRACER option only if
> DYNAMIC_FTRACE_WITH_REGS is enabled.
>
> +config CC_HAS_BRANCH_PROT_NONE
> + # GCC 9 or later, clang 8 or later
> + def_bool $(cc-option,-mbranch-protection=none)
> +
> config CC_HAS_BRANCH_PROT_PAC_RET
> # GCC 9 or later, clang 8 or later
> def_bool $(cc-option,-mbranch-protection=pac-ret+leaf)
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index f15f92ba53e6..370fca6663c8 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -65,6 +65,10 @@ stack_protector_prepare: prepare0
> include/generated/asm-offsets.h))
> endif
>
> +# Ensure that if the compiler supports branch protection we default it
> +# off, this will be overridden if we are using branch protection.
> +branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_NONE) := -mbranch-protection=none
> +
> ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
> branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all
> branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf
> @@ -73,9 +77,10 @@ branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pa
> # we pass it only to the assembler. This option is utilized only in case of non
> # integrated assemblers.
> branch-prot-flags-$(CONFIG_AS_HAS_PAC) += -Wa,-march=armv8.3-a
> -KBUILD_CFLAGS += $(branch-prot-flags-y)
> endif
>
> +KBUILD_CFLAGS += $(branch-prot-flags-y)
> +
> ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
> KBUILD_CPPFLAGS += -mbig-endian
> CHECKFLAGS += -D__AARCH64EB__
> --
> 2.20.1
>
--
Kees Cook
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Always force a branch protection mode when the compiler has one
2020-03-31 19:44 [PATCH] arm64: Always force a branch protection mode when the compiler has one Mark Brown
2020-03-31 19:46 ` Kees Cook
@ 2020-04-01 9:55 ` Mark Rutland
2020-04-01 17:54 ` Catalin Marinas
2 siblings, 0 replies; 5+ messages in thread
From: Mark Rutland @ 2020-04-01 9:55 UTC (permalink / raw)
To: Mark Brown
Cc: Kees Cook, Szabolcs Nagy, Catalin Marinas, stable,
Amit Daniel Kachhap, Will Deacon, linux-arm-kernel
On Tue, Mar 31, 2020 at 08:44:59PM +0100, Mark Brown wrote:
> Compilers with branch protection support can be configured to enable it by
> default, it is likely that distributions will do this as part of deploying
> branch protection system wide. As well as the slight overhead from having
> some extra NOPs for unused branch protection features this can cause more
> serious problems when the kernel is providing pointer authentication to
> userspace but not built for pointer authentication itself. In that case our
> switching of keys for userspace can affect the kernel unexpectedly, causing
> pointer authentication instructions in the kernel to corrupt addresses.
>
> To ensure that we get consistent and reliable behaviour always explicitly
> initialise the branch protection mode, ensuring that the kernel is built
> the same way regardless of the compiler defaults.
>
> Fixes: 7503197562567 (arm64: add basic pointer authentication support)
> Reported-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> Cc: stable@vger.kernel.org
Acked-by: Mark Rutland <mark.rutland@arm.com>
Mark.
> ---
> arch/arm64/Kconfig | 4 ++++
> arch/arm64/Makefile | 7 ++++++-
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index d3efdc095a17..1e46746e8392 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1537,6 +1537,10 @@ config ARM64_PTR_AUTH
> This feature works with FUNCTION_GRAPH_TRACER option only if
> DYNAMIC_FTRACE_WITH_REGS is enabled.
>
> +config CC_HAS_BRANCH_PROT_NONE
> + # GCC 9 or later, clang 8 or later
> + def_bool $(cc-option,-mbranch-protection=none)
> +
> config CC_HAS_BRANCH_PROT_PAC_RET
> # GCC 9 or later, clang 8 or later
> def_bool $(cc-option,-mbranch-protection=pac-ret+leaf)
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index f15f92ba53e6..370fca6663c8 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -65,6 +65,10 @@ stack_protector_prepare: prepare0
> include/generated/asm-offsets.h))
> endif
>
> +# Ensure that if the compiler supports branch protection we default it
> +# off, this will be overridden if we are using branch protection.
> +branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_NONE) := -mbranch-protection=none
> +
> ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
> branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all
> branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf
> @@ -73,9 +77,10 @@ branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pa
> # we pass it only to the assembler. This option is utilized only in case of non
> # integrated assemblers.
> branch-prot-flags-$(CONFIG_AS_HAS_PAC) += -Wa,-march=armv8.3-a
> -KBUILD_CFLAGS += $(branch-prot-flags-y)
> endif
>
> +KBUILD_CFLAGS += $(branch-prot-flags-y)
> +
> ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
> KBUILD_CPPFLAGS += -mbig-endian
> CHECKFLAGS += -D__AARCH64EB__
> --
> 2.20.1
>
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Always force a branch protection mode when the compiler has one
2020-03-31 19:44 [PATCH] arm64: Always force a branch protection mode when the compiler has one Mark Brown
2020-03-31 19:46 ` Kees Cook
2020-04-01 9:55 ` Mark Rutland
@ 2020-04-01 17:54 ` Catalin Marinas
2020-04-01 18:07 ` Mark Brown
2 siblings, 1 reply; 5+ messages in thread
From: Catalin Marinas @ 2020-04-01 17:54 UTC (permalink / raw)
To: Mark Brown
Cc: Mark Rutland, Kees Cook, Szabolcs Nagy, stable@vger.kernel.org,
Amit Kachhap, Will Deacon, linux-arm-kernel@lists.infradead.org
On Tue, Mar 31, 2020 at 08:44:59PM +0100, Mark Brown wrote:
> Compilers with branch protection support can be configured to enable it by
> default, it is likely that distributions will do this as part of deploying
> branch protection system wide. As well as the slight overhead from having
> some extra NOPs for unused branch protection features this can cause more
> serious problems when the kernel is providing pointer authentication to
> userspace but not built for pointer authentication itself.
With 5.7 you won't be able to configure user and kernel PAC support
independently. So, I guess that's something only for prior kernel
versions.
> In that case our
> switching of keys for userspace can affect the kernel unexpectedly, causing
> pointer authentication instructions in the kernel to corrupt addresses.
>
> To ensure that we get consistent and reliable behaviour always explicitly
> initialise the branch protection mode, ensuring that the kernel is built
> the same way regardless of the compiler defaults.
>
> Fixes: 7503197562567 (arm64: add basic pointer authentication support)
> Reported-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> Cc: stable@vger.kernel.org
> ---
> arch/arm64/Kconfig | 4 ++++
> arch/arm64/Makefile | 7 ++++++-
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index d3efdc095a17..1e46746e8392 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1537,6 +1537,10 @@ config ARM64_PTR_AUTH
> This feature works with FUNCTION_GRAPH_TRACER option only if
> DYNAMIC_FTRACE_WITH_REGS is enabled.
>
> +config CC_HAS_BRANCH_PROT_NONE
> + # GCC 9 or later, clang 8 or later
> + def_bool $(cc-option,-mbranch-protection=none)
I don't think we need to bother with a Kconfig entry here. We did it for
the other options since CONFIG_ARM64_PTR_AUTH has a dependency on them.
> +
> config CC_HAS_BRANCH_PROT_PAC_RET
> # GCC 9 or later, clang 8 or later
> def_bool $(cc-option,-mbranch-protection=pac-ret+leaf)
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index f15f92ba53e6..370fca6663c8 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -65,6 +65,10 @@ stack_protector_prepare: prepare0
> include/generated/asm-offsets.h))
> endif
>
> +# Ensure that if the compiler supports branch protection we default it
> +# off, this will be overridden if we are using branch protection.
> +branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_NONE) := -mbranch-protection=none
And a $(call cc-option,-mbranch-protection=none) here.
branch-prot-flags-y is only introduced in 5.7, so backporting may look
slightly weirder.
> +
> ifeq ($(CONFIG_ARM64_PTR_AUTH),y)
> branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all
> branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf
> @@ -73,9 +77,10 @@ branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pa
> # we pass it only to the assembler. This option is utilized only in case of non
> # integrated assemblers.
> branch-prot-flags-$(CONFIG_AS_HAS_PAC) += -Wa,-march=armv8.3-a
> -KBUILD_CFLAGS += $(branch-prot-flags-y)
> endif
>
> +KBUILD_CFLAGS += $(branch-prot-flags-y)
Or just use an else clause here with:
KBUILD_CFLAGS += ($call cc-option,-mbranch-protection=none).
On backports, we just drop else/endif since they don't exist.
Not a strong preference really, just looking to have backports resemble
upstream better. I can fix it up locally, whichever variant we go for
(or even this one).
--
Catalin
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Always force a branch protection mode when the compiler has one
2020-04-01 17:54 ` Catalin Marinas
@ 2020-04-01 18:07 ` Mark Brown
0 siblings, 0 replies; 5+ messages in thread
From: Mark Brown @ 2020-04-01 18:07 UTC (permalink / raw)
To: Catalin Marinas
Cc: Mark Rutland, Kees Cook, Szabolcs Nagy, stable@vger.kernel.org,
Amit Kachhap, Will Deacon, linux-arm-kernel@lists.infradead.org
[-- Attachment #1.1: Type: text/plain, Size: 963 bytes --]
On Wed, Apr 01, 2020 at 06:54:44PM +0100, Catalin Marinas wrote:
> On Tue, Mar 31, 2020 at 08:44:59PM +0100, Mark Brown wrote:
> > Compilers with branch protection support can be configured to enable it by
> > default, it is likely that distributions will do this as part of deploying
> > branch protection system wide. As well as the slight overhead from having
> > some extra NOPs for unused branch protection features this can cause more
> > serious problems when the kernel is providing pointer authentication to
> > userspace but not built for pointer authentication itself.
> With 5.7 you won't be able to configure user and kernel PAC support
> independently. So, I guess that's something only for prior kernel
> versions.
Yes, it's really for the benefit of stable at this point - hence the Cc.
Going forward it's hopefully more for defensiveness than anything else,
it's possible something similar might come up with some future stuff but
ideally not.
[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 484 bytes --]
[-- Attachment #2: Type: text/plain, Size: 176 bytes --]
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 5+ messages in thread