riscv/mm: manufacture shadow stack ptes

This patch implements the creation of a shadow stack pte on
riscv. Creating shadow stack PTE on riscv means clearing RWX and then
setting W=1.

Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Tested-by: Andreas Korb <andreas.korb@aisec.fraunhofer.de> # QEMU, custom CVA6
Tested-by: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Link: https://patch.msgid.link/20251112-v5_user_cfi_series-v23-7-b55691eacf4f@rivosinc.com
[pjw@kernel.org: cleaned up patch description]
Signed-off-by: Paul Walmsley <pjw@kernel.org>

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index b384a1a9327ef6981a79a588f83e12a0f363b716..153a692a56406e8e5595b5ad5e1622e48c721e97 100644 (file)
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -456,6 +456,11 @@ 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)
+{
+       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)
@@ -839,6 +844,11 @@ 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)
+{
+       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)));