Re: [PATCH v11 24/27] riscv: create a config for shadow stack and landing pad instr support

On Mon, Mar 10, 2025 at 11:44 PM Deepak Gupta debug@rivosinc.com wrote:

This patch creates a config for shadow stack support and landing pad instr support. Shadow stack support and landing instr support can be enabled by selecting `CONFIG_RISCV_USER_CFI`. Selecting `CONFIG_RISCV_USER_CFI` wires up path to enumerate CPU support and if cpu support exists, kernel will support cpu assisted user mode cfi.

If CONFIG_RISCV_USER_CFI is selected, select `ARCH_USES_HIGH_VMA_FLAGS`, `ARCH_HAS_USER_SHADOW_STACK` and DYNAMIC_SIGFRAME for riscv.

Signed-off-by: Deepak Gupta debug@rivosinc.com

arch/riscv/Kconfig | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 7612c52e9b1e..0a2e50f056e8 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -250,6 +250,26 @@ config ARCH_HAS_BROKEN_DWARF5 # https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471... depends on LD_IS_LLD && LLD_VERSION < 180000

+config RISCV_USER_CFI

•   def_bool y
  

•   bool "riscv userspace control flow integrity"
  

•   depends on 64BIT && $(cc-option,-mabi=lp64 -march=rv64ima_zicfiss)
  

•   depends on RISCV_ALTERNATIVE
  

•   select ARCH_HAS_USER_SHADOW_STACK
  

•   select ARCH_USES_HIGH_VMA_FLAGS
  

•   select DYNAMIC_SIGFRAME
  

•   help
  

•     Provides CPU assisted control flow integrity to userspace tasks.
  

•     Control flow integrity is provided by implementing shadow stack for
  

•     backward edge and indirect branch tracking for forward edge in program.
  

•     Shadow stack protection is a hardware feature that detects function
  

•     return address corruption. This helps mitigate ROP attacks.
  

•     Indirect branch tracking enforces that all indirect branches must land
  

•     on a landing pad instruction else CPU will fault. This mitigates against
  

•     JOP / COP attacks. Applications must be enabled to use it, and old user-
  

•     space does not get protection "for free".
  

•     default y
  

config ARCH_MMAP_RND_BITS_MIN default 18 if 64BIT default 8

LGTM.

Reviewed-by: Zong Li zong.li@sifive.com

-- 2.34.1

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