When a task does fork(), its Shadow Stack (SHSTK) must be duplicated for
the child. This patch implements a flow similar to copy-on-write of an
anonymous page, but for SHSTK.
A SHSTK PTE must be RO and Dirty. This Dirty bit requirement is used to
effect the copying. In copy_one_pte(), clear the Dirty bit from a SHSTK
PTE to cause a page fault upon the next SHSTK access. At that time, fix
the PTE and copy/re-use the page.
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
arch/x86/mm/pgtable.c | 15 +++++++++++++++
include/asm-generic/pgtable.h | 17 +++++++++++++++++
mm/memory.c | 7 ++++++-
3 files changed, 38 insertions(+), 1 deletion(-)
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 7bd2c3a52297..2eb33794c08d 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -872,3 +872,18 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
#endif /* CONFIG_X86_64 */
#endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */
+
+#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
+inline bool arch_copy_pte_mapping(vm_flags_t vm_flags)
+{
+ return (vm_flags & VM_SHSTK);
+}
+
+inline pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma)
+{
+ if (vma->vm_flags & VM_SHSTK)
+ return pte_mkdirty_shstk(pte);
+ else
+ return pte;
+}
+#endif /* CONFIG_X86_INTEL_SHADOW_STACK_USER */
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 798ea36a0549..9cb2f9ba5895 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -1190,6 +1190,23 @@ static inline bool arch_has_pfn_modify_check(void)
}
#endif /* !_HAVE_ARCH_PFN_MODIFY_ALLOWED */
+#ifdef CONFIG_MMU
+#ifndef CONFIG_ARCH_HAS_SHSTK
+static inline bool arch_copy_pte_mapping(vm_flags_t vm_flags)
+{
+ return false;
+}
+
+static inline pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma)
+{
+ return pte;
+}
+#else
+bool arch_copy_pte_mapping(vm_flags_t vm_flags);
+pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma);
+#endif
+#endif /* CONFIG_MMU */
+
/*
* Architecture PAGE_KERNEL_* fallbacks
*
diff --git a/mm/memory.c b/mm/memory.c
index 45442d9a4f52..6daa28614327 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -772,7 +772,8 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
* If it's a COW mapping, write protect it both
* in the parent and the child
*/
- if (is_cow_mapping(vm_flags) && pte_write(pte)) {
+ if ((is_cow_mapping(vm_flags) && pte_write(pte)) ||
+ arch_copy_pte_mapping(vm_flags)) {
ptep_set_wrprotect(src_mm, addr, src_pte);
pte = pte_wrprotect(pte);
}
@@ -2417,6 +2418,7 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
entry = pte_mkyoung(vmf->orig_pte);
entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+ entry = pte_set_vma_features(entry, vma);
if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
update_mmu_cache(vma, vmf->address, vmf->pte);
pte_unmap_unlock(vmf->pte, vmf->ptl);
@@ -2504,6 +2506,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
entry = mk_pte(new_page, vma->vm_page_prot);
entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+ entry = pte_set_vma_features(entry, vma);
/*
* Clear the pte entry and flush it first, before updating the
* pte with the new entry. This will avoid a race condition
@@ -3023,6 +3026,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
pte = mk_pte(page, vma->vm_page_prot);
if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page, NULL)) {
pte = maybe_mkwrite(pte_mkdirty(pte), vma);
+ pte = pte_set_vma_features(pte, vma);
vmf->flags &= ~FAULT_FLAG_WRITE;
ret |= VM_FAULT_WRITE;
exclusive = RMAP_EXCLUSIVE;
@@ -3165,6 +3169,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
entry = mk_pte(page, vma->vm_page_prot);
if (vma->vm_flags & VM_WRITE)
entry = pte_mkwrite(pte_mkdirty(entry));
+ entry = pte_set_vma_features(entry, vma);
vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
&vmf->ptl);
--
2.21.0
