linux-kernel - Re: [PATCH v3 11/29] riscv mm: manufacture shadow stack pte

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Date: Sun, 12 May 2024 18:26:51 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Deepak Gupta <debug@...osinc.com>, paul.walmsley@...ive.com,
 rick.p.edgecombe@...el.com, broonie@...nel.org, Szabolcs.Nagy@....com,
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Subject: Re: [PATCH v3 11/29] riscv mm: manufacture shadow stack pte

On 04/04/2024 01:34, Deepak Gupta wrote:
> This patch implements creating shadow stack pte (on riscv). Creating
> shadow stack PTE on riscv means that clearing RWX and then setting W=1.
>
> Signed-off-by: Deepak Gupta <debug@...osinc.com>
> ---
>   arch/riscv/include/asm/pgtable.h | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 4d5983bc6766..6362407f1e83 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -408,6 +408,12 @@ static inline pte_t pte_mkwrite_novma(pte_t pte)
>   	return __pte(pte_val(pte) | _PAGE_WRITE);
>   }
>   
> +static inline pte_t pte_mkwrite_shstk(pte_t pte)
> +{
> +	/* shadow stack on risc-v is XWR = 010. Clear everything and only set _PAGE_WRITE */


Nit: Not sure the comment is necessary


> +	return __pte((pte_val(pte) & ~(_PAGE_LEAF)) | _PAGE_WRITE);
> +}
> +
>   /* static inline pte_t pte_mkexec(pte_t pte) */
>   
>   static inline pte_t pte_mkdirty(pte_t pte)
> @@ -693,6 +699,12 @@ static inline pmd_t pmd_mkwrite_novma(pmd_t pmd)
>   	return pte_pmd(pte_mkwrite_novma(pmd_pte(pmd)));
>   }
>   
> +static inline pmd_t pmd_mkwrite_shstk(pmd_t pte)
> +{
> +	/* shadow stack on risc-v is XWR = 010. Clear everything and only set _PAGE_WRITE */
> +	return __pmd((pmd_val(pte) & ~(_PAGE_LEAF)) | _PAGE_WRITE);
> +}
> +
>   static inline pmd_t pmd_wrprotect(pmd_t pmd)
>   {
>   	return pte_pmd(pte_wrprotect(pmd_pte(pmd)));

Otherwise:

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

Thanks,

Alex