[RFC PATCH v9 16/27] mm: Update can_follow_write_pte() for Shadow Stack
From: Yu-cheng Yu <hidden>
Date: 2020-02-05 18:21:44
Also in:
linux-arch, linux-doc, linux-mm, lkml
Subsystem:
generic include/asm header files, memory management, memory management - gup (get user pages), memory management - thp (transparent huge page), the rest, x86 architecture (32-bit and 64-bit), x86 mm · Maintainers:
Arnd Bergmann, Andrew Morton, David Hildenbrand, Lorenzo Stoakes, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, Andy Lutomirski, Peter Zijlstra
Can_follow_write_pte() verifies that a read-only page is the task's own copy by ensuring the page has gone through faultin_page() and the PTE is Dirty. A Shadow Stack (SHSTK) PTE must be (read-only + _PAGE_DIRTY_HW). When a task does fork(), its SHSTK PTEs become (read-only + _PAGE_DIRTY_SW). This causes the next SHSTK access (i.e. CALL, RET, INCSSP) to trigger a fault; the page is then copied, and (read-only + _PAGE_DIRTY_HW) is restored. To update can_follow_write_pte() for SHSTK, introduce pte_exclusive(). It verifies a data PTE is Dirty and a SHSTK PTE has _PAGE_DIRTY_HW. Also rename can_follow_write_pte() to can_follow_write() to make its meaning clear; i.e. "Can we write to the page?", not "Is the PTE writable?" Also apply same changes to the huge memory case. Signed-off-by: Yu-cheng Yu <redacted> --- arch/x86/mm/pgtable.c | 18 ++++++++++++++++++ include/asm-generic/pgtable.h | 12 ++++++++++++ mm/gup.c | 8 +++++--- mm/huge_memory.c | 8 +++++--- 4 files changed, 40 insertions(+), 6 deletions(-)
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 3340b1d4e9da..fa8133f37918 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c@@ -887,6 +887,15 @@ inline pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma) return pte; } +inline bool pte_exclusive(pte_t pte, struct vm_area_struct *vma) +{ + if (vma->vm_flags & VM_SHSTK) + return pte_dirty_hw(pte); + else + return pte_dirty(pte); +} + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE inline pmd_t pmd_set_vma_features(pmd_t pmd, struct vm_area_struct *vma) { if (vma->vm_flags & VM_SHSTK)
@@ -894,4 +903,13 @@ inline pmd_t pmd_set_vma_features(pmd_t pmd, struct vm_area_struct *vma) else return pmd; } + +inline bool pmd_exclusive(pmd_t pmd, struct vm_area_struct *vma) +{ + if (vma->vm_flags & VM_SHSTK) + return pmd_dirty_hw(pmd); + else + return pmd_dirty(pmd); +} +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */ #endif /* CONFIG_X86_INTEL_SHADOW_STACK_USER */
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index a9df093fdf45..ae9a84fffc25 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h@@ -1202,18 +1202,30 @@ static inline pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma) return pte; } +static inline bool pte_exclusive(pte_t pte, struct vm_area_struct *vma) +{ + return pte_dirty(pte); +} + #ifdef CONFIG_TRANSPARENT_HUGEPAGE static inline pmd_t pmd_set_vma_features(pmd_t pmd, struct vm_area_struct *vma) { return pmd; } + +static inline bool pmd_exclusive(pmd_t pmd, struct vm_area_struct *vma) +{ + return pmd_dirty(pmd); +} #endif #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); +bool pte_exclusive(pte_t pte, struct vm_area_struct *vma); #ifdef CONFIG_TRANSPARENT_HUGEPAGE pmd_t pmd_set_vma_features(pmd_t pmd, struct vm_area_struct *vma); +bool pmd_exclusive(pmd_t pmd, struct vm_area_struct *vma); #endif #endif #endif /* CONFIG_MMU */
diff --git a/mm/gup.c b/mm/gup.c
index 7646bf993b25..d1dbfbde8443 100644
--- a/mm/gup.c
+++ b/mm/gup.c@@ -164,10 +164,12 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address, * FOLL_FORCE can write to even unwritable pte's, but only * after we've gone through a COW cycle and they are dirty. */ -static inline bool can_follow_write_pte(pte_t pte, unsigned int flags) +static inline bool can_follow_write(pte_t pte, unsigned int flags, + struct vm_area_struct *vma) { return pte_write(pte) || - ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte)); + ((flags & FOLL_FORCE) && (flags & FOLL_COW) && + pte_exclusive(pte, vma)); } static struct page *follow_page_pte(struct vm_area_struct *vma,
@@ -205,7 +207,7 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, } if ((flags & FOLL_NUMA) && pte_protnone(pte)) goto no_page; - if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) { + if ((flags & FOLL_WRITE) && !can_follow_write(pte, flags, vma)) { pte_unmap_unlock(ptep, ptl); return NULL; }
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 93ef368df2dd..baad346e9f4a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c@@ -1469,10 +1469,12 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd) * FOLL_FORCE can write to even unwritable pmd's, but only * after we've gone through a COW cycle and they are dirty. */ -static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags) +static inline bool can_follow_write(pmd_t pmd, unsigned int flags, + struct vm_area_struct *vma) { return pmd_write(pmd) || - ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd)); + ((flags & FOLL_FORCE) && (flags & FOLL_COW) && + pmd_exclusive(pmd, vma)); } struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
@@ -1485,7 +1487,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, assert_spin_locked(pmd_lockptr(mm, pmd)); - if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags)) + if (flags & FOLL_WRITE && !can_follow_write(*pmd, flags, vma)) goto out; /* Avoid dumping huge zero page */
--
2.21.0