[PATCH v12 03/28] riscv: zicfiss / zicfilp enumeration

Deepak Gupta
2025-03-14T21:39:35Z

This patch adds support for detecting zicfiss and zicfilp. zicfiss and
zicfilp stands for unprivleged integer spec extension for shadow stack
and branch tracking on indirect branches, respectively.

This patch looks for zicfiss and zicfilp in device tree and accordinlgy
lights up bit in cpu feature bitmap. Furthermore this patch adds detection
utility functions to return whether shadow stack or landing pads are
supported by cpu.

Reviewed-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
arch/riscv/include/asm/cpufeature.h | 13 +++++++++++++
arch/riscv/include/asm/hwcap.h | 2 ++
arch/riscv/include/asm/processor.h | 1 +
arch/riscv/kernel/cpufeature.c | 13 +++++++++++++
4 files changed, 29 insertions(+)

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index 569140d6e639..69007b8100ca 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -12,6 +12,7 @@
#include <linux/kconfig.h>
#include <linux/percpu-defs.h>
#include <linux/threads.h>
+#include <linux/smp.h>
#include <asm/hwcap.h>
#include <asm/cpufeature-macros.h>

@@ -137,4 +138,16 @@ static __always_inline bool riscv_cpu_has_extension_unlikely(int cpu, const unsi
return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
}

+static inline bool cpu_supports_shadow_stack(void)
+{
+ return (IS_ENABLED(CONFIG_RISCV_USER_CFI) &&
+ riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICFISS));
+}
+
+static inline bool cpu_supports_indirect_br_lp_instr(void)
+{
+ return (IS_ENABLED(CONFIG_RISCV_USER_CFI) &&
+ riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICFILP));
+}
+
#endif
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 869da082252a..2dc4232bdb3e 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -100,6 +100,8 @@
#define RISCV_ISA_EXT_ZICCRSE 91
#define RISCV_ISA_EXT_SVADE 92
#define RISCV_ISA_EXT_SVADU 93
+#define RISCV_ISA_EXT_ZICFILP 94
+#define RISCV_ISA_EXT_ZICFISS 95

#define RISCV_ISA_EXT_XLINUXENVCFG 127

diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 5f56eb9d114a..e3aba3336e63 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -13,6 +13,7 @@
#include <vdso/processor.h>

#include <asm/ptrace.h>
+#include <asm/hwcap.h>

#define arch_get_mmap_end(addr, len, flags) \
({ \
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index c6ba750536c3..82065cc55822 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -150,6 +150,15 @@ static int riscv_ext_svadu_validate(const struct riscv_isa_ext_data *data,
return 0;
}

+static int riscv_cfi_validate(const struct riscv_isa_ext_data *data,
+ const unsigned long *isa_bitmap)
+{
+ if (!IS_ENABLED(CONFIG_RISCV_USER_CFI))
+ return -EINVAL;
+
+ return 0;
+}
+
static const unsigned int riscv_zk_bundled_exts[] = {
RISCV_ISA_EXT_ZBKB,
RISCV_ISA_EXT_ZBKC,
@@ -333,6 +342,10 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
__RISCV_ISA_EXT_SUPERSET_VALIDATE(zicboz, RISCV_ISA_EXT_ZICBOZ, riscv_xlinuxenvcfg_exts,
riscv_ext_zicboz_validate),
__RISCV_ISA_EXT_DATA(ziccrse, RISCV_ISA_EXT_ZICCRSE),
+ __RISCV_ISA_EXT_SUPERSET_VALIDATE(zicfilp, RISCV_ISA_EXT_ZICFILP, riscv_xlinuxenvcfg_exts,
+ riscv_cfi_validate),
+ __RISCV_ISA_EXT_SUPERSET_VALIDATE(zicfiss, RISCV_ISA_EXT_ZICFISS, riscv_xlinuxenvcfg_exts,
+ riscv_cfi_validate),
__RISCV_ISA_EXT_DATA(zicntr, RISCV_ISA_EXT_ZICNTR),
__RISCV_ISA_EXT_DATA(zicond, RISCV_ISA_EXT_ZICOND),
__RISCV_ISA_EXT_DATA(zicsr, RISCV_ISA_EXT_ZICSR),

--
2.34.1