linux-kernel - [RFC PATCH v2 16/27] mm: Modify can_follow_write

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Date:   Tue, 10 Jul 2018 15:26:28 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omiun.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [RFC PATCH v2 16/27] mm: Modify can_follow_write_pte/pmd for shadow stack

There are three possible shadow stack PTE settings:

  Normal SHSTK PTE: (R/O + DIRTY_HW)
  SHSTK PTE COW'ed: (R/O + DIRTY_HW)
  SHSTK PTE shared as R/O data: (R/O + DIRTY_SW)

Update can_follow_write_pte/pmd for the shadow stack.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
---
 mm/gup.c         | 11 ++++++++---
 mm/huge_memory.c | 10 +++++++---
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index b70d7ba7cc13..00171ee847af 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -64,10 +64,13 @@ 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(pte_t pte, unsigned int flags,
+					bool shstk)
 {
+	bool pte_cowed = shstk ? is_shstk_pte(pte):pte_dirty(pte);
+
 	return pte_write(pte) ||
-		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
+		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_cowed);
 }
 
 static struct page *follow_page_pte(struct vm_area_struct *vma,
@@ -78,7 +81,9 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 	struct page *page;
 	spinlock_t *ptl;
 	pte_t *ptep, pte;
+	bool shstk;
 
+	shstk = is_shstk_mapping(vma->vm_flags);
 retry:
 	if (unlikely(pmd_bad(*pmd)))
 		return no_page_table(vma, flags);
@@ -105,7 +110,7 @@ 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(pte, flags, shstk)) {
 		pte_unmap_unlock(ptep, ptl);
 		return NULL;
 	}
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7f3e11d3b64a..db4c689a960a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1389,10 +1389,13 @@ int 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(pmd_t pmd, unsigned int flags,
+					bool shstk)
 {
+	bool pmd_cowed = shstk ? is_shstk_pmd(pmd):pmd_dirty(pmd);
+
 	return pmd_write(pmd) ||
-	       ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
+	       ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_cowed);
 }
 
 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
@@ -1402,10 +1405,11 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 {
 	struct mm_struct *mm = vma->vm_mm;
 	struct page *page = NULL;
+	bool shstk = is_shstk_mapping(vma->vm_flags);
 
 	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(*pmd, flags, shstk))
 		goto out;
 
 	/* Avoid dumping huge zero page */
-- 
2.17.1