linux-kernel - Re: [RFC PATCH v1 05/28] riscv: zicfiss/zicfilp enumeration

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Date: Thu, 25 Jan 2024 17:59:24 +0000
From: Conor Dooley <conor@...nel.org>
To: debug@...osinc.com
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Subject: Re: [RFC PATCH v1 05/28] riscv: zicfiss/zicfilp enumeration

Yo,

Series is RFC, so not gonna review it in depth, just wanted to comment
on this particular patch.

On Wed, Jan 24, 2024 at 10:21:30PM -0800, debug@...osinc.com wrote:
> From: Deepak Gupta <debug@...osinc.com>
> 
> 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.
> 
> Signed-off-by: Deepak Gupta <debug@...osinc.com>
> ---
>  arch/riscv/include/asm/cpufeature.h | 18 ++++++++++++++++++
>  arch/riscv/include/asm/hwcap.h      |  2 ++
>  arch/riscv/include/asm/processor.h  |  1 +
>  arch/riscv/kernel/cpufeature.c      |  2 ++
>  4 files changed, 23 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index a418c3112cd6..216190731c55 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -133,4 +133,22 @@ 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)
> +{
> +#ifdef CONFIG_RISCV_USER_CFI

In passing, I don't see any reason for not using IS_ENABLED() here.

> +	return riscv_isa_extension_available(NULL, ZICFISS);
> +#else
> +	return false;
> +#endif
> +}
> +
> +static inline bool cpu_supports_indirect_br_lp_instr(void)
> +{
> +#ifdef CONFIG_RISCV_USER_CFI
> +	return riscv_isa_extension_available(NULL, ZICFILP);
> +#else
> +	return false;
> +#endif
> +}
> +
>  #endif
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 06d30526ef3b..918165cfb4fa 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -57,6 +57,8 @@
>  #define RISCV_ISA_EXT_ZIHPM		42
>  #define RISCV_ISA_EXT_SMSTATEEN		43
>  #define RISCV_ISA_EXT_ZICOND		44
> +#define RISCV_ISA_EXT_ZICFISS	45
> +#define RISCV_ISA_EXT_ZICFILP	46
>  
>  #define RISCV_ISA_EXT_MAX		64
>  
> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> index f19f861cda54..ee2f51787ff8 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>
>  
>  #ifdef CONFIG_64BIT
>  #define DEFAULT_MAP_WINDOW	(UL(1) << (MMAP_VA_BITS - 1))
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 98623393fd1f..16624bc9a46b 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -185,6 +185,8 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>  	__RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
>  	__RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
>  	__RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
> +	__RISCV_ISA_EXT_DATA(zicfiss, RISCV_ISA_EXT_ZICFISS),
> +	__RISCV_ISA_EXT_DATA(zicfilp, RISCV_ISA_EXT_ZICFILP),

Anything you add to this array, you need to document in a dt-binding.
Also, you added these in the wrong place. There's a massive comment
before the array describing the order entries must be in, please take a
look.

Thanks,
Conor.

>  };
>  
>  const size_t riscv_isa_ext_count = ARRAY_SIZE(riscv_isa_ext);
> -- 
> 2.43.0
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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