If a VMA has the VM_SHADOW_STACK flag, it is shadow stack memory. So
when it is made writable with pte_mkwrite(), it should create shadow
stack memory, not conventionally writable memory. Now that all the places
where shadow stack memory might be created pass a VMA into pte_mkwrite(),
it can know when it should do this.

So make pte_mkwrite() create shadow stack memory when the VMA has the
VM_SHADOW_STACK flag. Do the same thing for pmd_mkwrite().

This requires referencing VM_SHADOW_STACK in these functions, which are
currently defined in pgtable.h, however mm.h (where VM_SHADOW_STACK is
located) can't be pulled in without causing problems for files that
reference pgtable.h. So also move pte/pmd_mkwrite() into pgtable.c, where
they can safely reference VM_SHADOW_STACK.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Kees Cook <redacted>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Acked-by: Deepak Gupta <redacted>
Tested-by: Pengfei Xu <redacted>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <redacted>
---
 arch/x86/mm/pgtable.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 101e721d74aa..c4b222d3b1b4 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c

@@ -883,6 +883,9 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
 
 pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma)
 {
+	if (vma->vm_flags & VM_SHADOW_STACK)
+		return pte_mkwrite_shstk(pte);
+
 	pte = pte_mkwrite_novma(pte);
 
 	return pte_clear_saveddirty(pte);

@@ -890,6 +893,9 @@ pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma)
 
 pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 {
+	if (vma->vm_flags & VM_SHADOW_STACK)
+		return pmd_mkwrite_shstk(pmd);
+
 	pmd = pmd_mkwrite_novma(pmd);
 
 	return pmd_clear_saveddirty(pmd);

-- 
2.34.1