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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id k2sm951328pjl.23.2019.05.29.20.45.23 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 29 May 2019 20:45:23 -0700 (PDT) Date: Wed, 29 May 2019 20:45:22 -0700 From: Kees Cook To: Kristina Martsenko Subject: Re: [RFC v2 7/7] arm64: compile the kernel with ptrauth return address signing Message-ID: <201905292041.5297BF8C2F@keescook> References: <20190529190332.29753-1-kristina.martsenko@arm.com> <20190529190332.29753-8-kristina.martsenko@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190529190332.29753-8-kristina.martsenko@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190529_204529_571078_D3DA50B8 X-CRM114-Status: GOOD ( 31.27 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Ard Biesheuvel , Catalin Marinas , Suzuki K Poulose , Will Deacon , Ramana Radhakrishnan , Amit Kachhap , Dave Martin , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, May 29, 2019 at 08:03:32PM +0100, Kristina Martsenko wrote: > Compile all non-leaf functions with two ptrauth instructions: PACIASP in > the prologue to sign the return address, and AUTIASP in the epilogue to > authenticate the return address (from the stack). If authentication > fails, the return will cause an instruction abort to be taken, followed > by an oops and killing the task. This should help protect the kernel > against attacks using return-oriented programming. > > The new instructions are in the HINT encoding space, so on a system > without ptrauth they execute as NOPs. > > CONFIG_ARM64_PTR_AUTH now not only enables ptrauth for userspace and KVM > guests, but also automatically builds the kernel with ptrauth > instructions if the compiler supports it. If there is no compiler > support, we do not warn that the kernel was built without ptrauth > instructions. > > GCC 7 and 8 support the -msign-return-address option, while GCC 9 > deprecates that option and replaces it with -mbranch-protection. Support > both options. > > Signed-off-by: Kristina Martsenko Minor nits below... Reviewed-by: Kees Cook > --- > > Changes since RFC v1: > - Fixed support for compilers without ptrauth > - Added support for the new -mbranch-protection option > - Switched from protecting all functions to only protecting non-leaf functions > (for no good reason, I have not done e.g. gadget analysis) > - Moved __no_ptrauth definition to this patch, depending on compiler support > - Updated the Kconfig symbol description > - Updated the commit message > > arch/arm64/Kconfig | 12 +++++++++++- > arch/arm64/Makefile | 6 ++++++ > arch/arm64/include/asm/pointer_auth.h | 6 ++++++ > 3 files changed, 23 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index f4c1e9b30129..3ce93d88fae1 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -1295,11 +1295,15 @@ config ARM64_PTR_AUTH > and other attacks. > > This option enables these instructions at EL0 (i.e. for userspace). > - > Choosing this option will cause the kernel to initialise secret keys > for each process at exec() time, with these keys being > context-switched along with the process. > > + If the compiler supports the -mbranch-protection or > + -msign-return-address flag (e.g. GCC 7 or later), then this option > + will also cause the kernel itself to be compiled with return address > + protection. > + > The feature is detected at runtime. If the feature is not present in > hardware it will not be advertised to userspace nor will it be > enabled. > @@ -1308,6 +1312,12 @@ config ARM64_PTR_AUTH > then the secondary CPU will be offlined. On such a system, this > option should not be selected. > > +config CC_HAS_BRANCH_PROT_PAC_RET > + def_bool $(cc-option,-mbranch-protection=pac-ret) > + > +config CC_HAS_SIGN_RETURN_ADDRESS > + def_bool $(cc-option,-msign-return-address=non-leaf) > + I would add comments here for "GCC 9, Clang" and "GCC 7, 8" respectively, just so it's quickly obvious what's to be expected when reading this later. :) > endmenu > > config ARM64_SVE > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index b025304bde46..1dfbe755b531 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -66,6 +66,12 @@ stack_protector_prepare: prepare0 > include/generated/asm-offsets.h)) > endif > > +ifeq ($(CONFIG_ARM64_PTR_AUTH),y) > +pac-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=non-leaf > +pac-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret > +KBUILD_CFLAGS += $(pac-flags-y) > +endif > + > ifeq ($(CONFIG_CPU_BIG_ENDIAN), y) > KBUILD_CPPFLAGS += -mbig-endian > CHECKFLAGS += -D__AARCH64EB__ > diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h > index 5491c34b4dc3..3a83c40ffd8a 100644 > --- a/arch/arm64/include/asm/pointer_auth.h > +++ b/arch/arm64/include/asm/pointer_auth.h > @@ -15,7 +15,13 @@ > * allows pointer authentication to be enabled/disabled within the function > * (but leaves the function unprotected by pointer authentication). > */ > +#if defined(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) > +#define __no_ptrauth __attribute__((target("branch-protection=none"))) > +#elif defined(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) > +#define __no_ptrauth __attribute__((target("sign-return-address=none"))) > +#else > #define __no_ptrauth > +#endif Is arch/arm64/include/asm/pointer_auth.h going to be included always? I suspect the correct place for this might end up being in include/linux/compiler_types.h, but for now, only a few select places need it, so this is probably fine as-is. > > /* > * Each key is a 128-bit quantity which is split across a pair of 64-bit > -- > 2.11.0 > I'm excited to test this series! :) -- Kees Cook _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel