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Message-Id: <20250724-riscv_kcfi-v1-11-04b8fa44c98c@rivosinc.com> Date: Thu, 24 Jul 2025 16:37:04 -0700 From: Deepak Gupta <debug@...osinc.com> To: Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>, Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas.schier@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...hat.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, Monk Chiang <monk.chiang@...ive.com>, Kito Cheng <kito.cheng@...ive.com>, Justin Stitt <justinstitt@...gle.com> Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, linux-mm@...ck.org, llvm@...ts.linux.dev, rick.p.edgecombe@...el.com, broonie@...nel.org, cleger@...osinc.com, samitolvanen@...gle.com, apatel@...tanamicro.com, ajones@...tanamicro.com, conor.dooley@...rochip.com, charlie@...osinc.com, samuel.holland@...ive.com, bjorn@...osinc.com, fweimer@...hat.com, jeffreyalaw@...il.com, heinrich.schuchardt@...onical.com, andrew@...ive.com, ved@...osinc.com, Deepak Gupta <debug@...osinc.com> Subject: [PATCH 11/11] riscv: Kconfig & Makefile for riscv kernel control flow integrity Defines `CONFIG_RISCV_KERNEL_CFI` and selects SHADOW_CALL_STACK and ARCH_HAS_KERNEL_SHADOW_STACK both so that zicfiss can be wired up. Makefile checks if CONFIG_RISCV_KERNEL_CFI is enabled, then light up zicfiss and zicfilp compiler flags. CONFIG_RISCV_KERNEL_CFI is dependent on CONFIG_RISCV_USER_CFI. There is no reason for user to not select support for user cfi while enabling for kernel. compat vdso don't need fcf-protection (toolchain lacks support). Signed-off-by: Deepak Gupta <debug@...osinc.com> --- arch/riscv/Kconfig | 37 +++++++++++++++++++++++++++++++++- arch/riscv/Makefile | 8 ++++++++ arch/riscv/kernel/compat_vdso/Makefile | 2 +- arch/riscv/kernel/vdso/Makefile | 2 +- 4 files changed, 46 insertions(+), 3 deletions(-) diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 385c3d93e378..305ba5787f74 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -245,7 +245,7 @@ config GCC_SUPPORTS_DYNAMIC_FTRACE depends on CC_HAS_MIN_FUNCTION_ALIGNMENT || !RISCV_ISA_C config HAVE_SHADOW_CALL_STACK - def_bool $(cc-option,-fsanitize=shadow-call-stack) + def_bool $(cc-option,-fsanitize=shadow-call-stack) || $(cc-option,-mabi=lp64 -march=rv64ima_zicfilp_zicfiss) # https://github.com/riscv-non-isa/riscv-elf-psabi-doc/commit/a484e843e6eeb51f0cb7b8819e50da6d2444d769 depends on $(ld-option,--no-relax-gp) @@ -864,6 +864,16 @@ config RISCV_ISA_ZICBOP If you don't know what to do here, say Y. +config TOOLCHAIN_HAS_ZICFILP + bool + default y + depends on 64BIT && $(cc-option,-mabi=lp64 -march=rv64ima_zicfilp) + +config TOOLCHAIN_HAS_ZICFISS + bool + default y + depends on 64BIT && $(cc-option,-mabi=lp64 -march=rv64ima_zicfiss) + config TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI def_bool y # https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=aed44286efa8ae8717a77d94b51ac3614e2ca6dc @@ -1182,6 +1192,31 @@ config RISCV_USER_CFI space does not get protection "for free". default n. +config RISCV_KERNEL_CFI + def_bool n + bool "hw assisted riscv kernel control flow integrity (kcfi)" + depends on 64BIT && $(cc-option,-mabi=lp64 -march=rv64ima_zicfilp_zicfiss) + depends on RISCV_USER_CFI + select ARCH_SUPPORTS_SHADOW_CALL_STACK + select SHADOW_CALL_STACK + select ARCH_HAS_KERNEL_SHADOW_STACK + help + Provides CPU assisted control flow integrity to for riscv kernel. + Control flow integrity is provided by implementing shadow stack for + backward edge and indirect branch tracking for forward edge. Shadow + stack protection is a hardware feature that detects function return + address corruption. This helps mitigate ROP attacks. RISCV_KERNEL_CFI + selects CONFIG_SHADOW_CALL_STACK which uses software based shadow + stack but is unprotected against stray writes. Selecting RISCV_KERNEL_CFI + will select CONFIG_DYNAMIC_SCS and will enable hardware assisted shadow + stack protection against stray writes. + Indirect branch tracking enforces that all indirect branches must land + on a landing pad instruction else CPU will fault. This enables forward + control flow (call/jmp) protection in kernel and restricts all indirect + call or jump in kernel to a landing pad instruction which mostly likely + will be start of the function. + default n + endmenu # "Kernel features" menu "Boot options" diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile index 7128df832b28..6ef30a3d2bc4 100644 --- a/arch/riscv/Makefile +++ b/arch/riscv/Makefile @@ -61,8 +61,10 @@ else ifeq ($(CONFIG_LTO_CLANG),y) endif ifeq ($(CONFIG_SHADOW_CALL_STACK),y) +ifndef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK KBUILD_LDFLAGS += --no-relax-gp endif +endif # ISA string setting riscv-march-$(CONFIG_ARCH_RV32I) := rv32ima @@ -91,6 +93,12 @@ riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZABHA) := $(riscv-march-y)_zabha KBUILD_BASE_ISA = -march=$(shell echo $(riscv-march-y) | sed -E 's/(rv32ima|rv64ima)fd([^v_]*)v?/\1\2/') export KBUILD_BASE_ISA +ifeq ($(CONFIG_RISCV_KERNEL_CFI),y) +riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZICFILP) := $(riscv-march-y)_zicfilp +riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZICFISS) := $(riscv-march-y)_zicfiss +KBUILD_CFLAGS += -fcf-protection=full +KBUILD_AFLAGS += -fcf-protection=full +endif # Remove F,D,V from isa string for all. Keep extensions between "fd" and "v" by # matching non-v and non-multi-letter extensions out with the filter ([^v_]*) KBUILD_CFLAGS += $(KBUILD_BASE_ISA) diff --git a/arch/riscv/kernel/compat_vdso/Makefile b/arch/riscv/kernel/compat_vdso/Makefile index 24e37d1ef7ec..552131bc34d7 100644 --- a/arch/riscv/kernel/compat_vdso/Makefile +++ b/arch/riscv/kernel/compat_vdso/Makefile @@ -69,4 +69,4 @@ quiet_cmd_compat_vdsold = VDSOLD $@ # actual build commands quiet_cmd_compat_vdsoas = VDSOAS $@ - cmd_compat_vdsoas = $(COMPAT_CC) $(a_flags) $(COMPAT_CC_FLAGS) -c -o $@ $< + cmd_compat_vdsoas = $(COMPAT_CC) $(filter-out -fcf-protection=full, $(a_flags)) $(COMPAT_CC_FLAGS) -c -o $@ $< diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile index 2b528d82fa7d..7b1446b63ebc 100644 --- a/arch/riscv/kernel/vdso/Makefile +++ b/arch/riscv/kernel/vdso/Makefile @@ -17,7 +17,7 @@ ifdef CONFIG_VDSO_GETRANDOM vdso-syms += getrandom endif -ifdef CONFIG_RISCV_USER_CFI +ifneq ($(CONFIG_RISCV_USER_CFI), $(CONFIG_RISCV_KERNEL_CFI)) CFI_MARCH = _zicfilp_zicfiss CFI_FULL = -fcf-protection=full endif -- 2.43.0
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