[PATCH v7 20/41] x86/mm: Teach pte_mkwrite() about stack memory

Rick Edgecombe
2023-02-27T22:32:34Z

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 pte_mkwrite()
takes a VMA, and places where shadow stack memory might be created pass
one, pte_mkwrite() 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.

Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>

---
v6:
- New patch
---
arch/x86/include/asm/pgtable.h | 20 ++------------------
arch/x86/mm/pgtable.c | 26 ++++++++++++++++++++++++++
2 files changed, 28 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 05dfdbdf96b4..d81e7ec27507 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -456,15 +456,7 @@ static inline pte_t pte_mkwrite_kernel(pte_t pte)

struct vm_area_struct;

-static inline pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma)
-{
- pte = pte_mkwrite_kernel(pte);
-
- if (pte_dirty(pte))
- pte = pte_clear_saveddirty(pte);
-
- return pte;
-}
+pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma);

static inline pte_t pte_mkhuge(pte_t pte)
{
@@ -601,15 +593,7 @@ static inline pmd_t pmd_mkyoung(pmd_t pmd)
return pmd_set_flags(pmd, _PAGE_ACCESSED);
}

-static inline pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
-{
- pmd = pmd_set_flags(pmd, _PAGE_RW);
-
- if (pmd_dirty(pmd))
- pmd = pmd_clear_saveddirty(pmd);
-
- return pmd;
-}
+pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);

static inline pud_t pud_set_flags(pud_t pud, pudval_t set)
{
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index e4f499eb0f29..98856bcc8102 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -880,3 +880,29 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)

#endif /* CONFIG_X86_64 */
#endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */
+
+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_kernel(pte);
+
+ if (pte_dirty(pte))
+ pte = pte_clear_saveddirty(pte);
+
+ return pte;
+}
+
+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_set_flags(pmd, _PAGE_RW);
+
+ if (pmd_dirty(pmd))
+ pmd = pmd_clear_saveddirty(pmd);
+
+ return pmd;
+}
--
2.17.1