On Thu, Dec 04, 2025 at 02:17:27PM -0800, Randy Dunlap wrote:
On 12/4/25 12:04 PM, Deepak Gupta 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.
Reviewed-by: Zong Li <[email protected]>
Tested-by: Andreas Korb <[email protected]>
Tested-by: Valentin Haudiquet <[email protected]>
Signed-off-by: Deepak Gupta <[email protected]>
---
arch/riscv/Kconfig | 22 ++++++++++++++++++++++
arch/riscv/configs/hardening.config | 4 ++++
2 files changed, 26 insertions(+)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 0c6038dc5dfd..f5574c6f66d8 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -1146,6 +1146,28 @@ config RANDOMIZE_BASE
If unsure, say N.
+config RISCV_USER_CFI
+ def_bool y
+ bool "riscv userspace control flow integrity"
+ depends on 64BIT && \
+ $(cc-option,-mabi=lp64 -march=rv64ima_zicfiss_zicfilp
-fcf-protection=full)
+ depends on RISCV_ALTERNATIVE
+ select RISCV_SBI
+ 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.
CPU-assisted
+ 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.
Default is y if hardware supports it.
?
No default Y means support is built in the kernel for cfi.
If hardware doesn't support CFI instructions, then kernel will do following
- prctls to manage shadow stack/landing pad enable/disable will fail.
- vDSO will not have shadow stack instructions in it.
+
endmenu # "Kernel features"
--
~Randy
