2024-04-03 23:45:04

by Deepak Gupta

Subject: [PATCH v3 11/29] riscv mm: manufacture shadow stack pte

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 <[email protected]>
---
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 */
+ 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)));
--
2.43.2

2024-05-12 16:28:17

by Alexandre Ghiti

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 <[email protected]>
> ---
> 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 <[email protected]>

Thanks,

Alex