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

Alexandre Ghiti
2025-04-07T15:48:40Z

On 14/03/2025 22:39, Deepak Gupta wrote:
> 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));

I would use riscv_has_extension_unlikely() instead of the cpu specific
variant, that would remove the need for #include <linux/smp.h>. Unless
you have a good reason to do that?

> +}
> +
> +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),
>

With the above comment fixed, you can add:

Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Thanks,

Alex