A RO and dirty PTE exists in the following cases:
(a) A page is modified and then shared with a fork()'ed child;
(b) A R/O page that has been COW'ed;
(c) A SHSTK page.
The processor does not read the dirty bit for (a) and (b), but
checks the dirty bit for (c). To prevent the use of non-SHSTK
memory as SHSTK, we introduce a spare bit of the 64-bit PTE as
_PAGE_BIT_DIRTY_SW and use that for (a) and (b). This results
to the following possible PTE settings:
Modified PTE: (R/W + DIRTY_HW)
Modified and shared PTE: (R/O + DIRTY_SW)
R/O PTE COW'ed: (R/O + DIRTY_SW)
SHSTK PTE: (R/O + DIRTY_HW)
SHSTK PTE COW'ed: (R/O + DIRTY_HW)
SHSTK PTE shared: (R/O + DIRTY_SW)
Note that _PAGE_BIT_DRITY_SW is only used in R/O PTEs but
not R/W PTEs.
When this patch is applied, there are six free bits left in
the 64-bit PTE. There is no more free bit in the 32-bit
PTE (except for PAE) and shadow stack is not implemented
for the 32-bit kernel.
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
arch/x86/include/asm/pgtable.h | 129 ++++++++++++++++++++++-----
arch/x86/include/asm/pgtable_types.h | 21 ++++-
2 files changed, 128 insertions(+), 22 deletions(-)
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 95c918ad84ed..3ee554d81480 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -119,9 +119,9 @@ extern pmdval_t early_pmd_flags;
* The following only work if pte_present() is true.
* Undefined behaviour if not..
*/
-static inline int pte_dirty(pte_t pte)
+static inline bool pte_dirty(pte_t pte)
{
- return pte_flags(pte) & _PAGE_DIRTY;
+ return pte_flags(pte) & _PAGE_DIRTY_BITS;
}
@@ -143,9 +143,9 @@ static inline int pte_young(pte_t pte)
return pte_flags(pte) & _PAGE_ACCESSED;
}
-static inline int pmd_dirty(pmd_t pmd)
+static inline bool pmd_dirty(pmd_t pmd)
{
- return pmd_flags(pmd) & _PAGE_DIRTY;
+ return pmd_flags(pmd) & _PAGE_DIRTY_BITS;
}
static inline int pmd_young(pmd_t pmd)
@@ -153,9 +153,9 @@ static inline int pmd_young(pmd_t pmd)
return pmd_flags(pmd) & _PAGE_ACCESSED;
}
-static inline int pud_dirty(pud_t pud)
+static inline bool pud_dirty(pud_t pud)
{
- return pud_flags(pud) & _PAGE_DIRTY;
+ return pud_flags(pud) & _PAGE_DIRTY_BITS;
}
static inline int pud_young(pud_t pud)
@@ -294,9 +294,23 @@ static inline pte_t pte_clear_flags(pte_t pte, pteval_t clear)
return native_make_pte(v & ~clear);
}
+#if defined(CONFIG_X86_INTEL_SHADOW_STACK_USER)
+static inline pte_t pte_move_flags(pte_t pte, pteval_t from, pteval_t to)
+{
+ if (pte_flags(pte) & from)
+ pte = pte_set_flags(pte_clear_flags(pte, from), to);
+ return pte;
+}
+#else
+static inline pte_t pte_move_flags(pte_t pte, pteval_t from, pteval_t to)
+{
+ return pte;
+}
+#endif
+
static inline pte_t pte_mkclean(pte_t pte)
{
- return pte_clear_flags(pte, _PAGE_DIRTY);
+ return pte_clear_flags(pte, _PAGE_DIRTY_BITS);
}
static inline pte_t pte_mkold(pte_t pte)
@@ -306,6 +320,7 @@ static inline pte_t pte_mkold(pte_t pte)
static inline pte_t pte_wrprotect(pte_t pte)
{
+ pte = pte_move_flags(pte, _PAGE_DIRTY_HW, _PAGE_DIRTY_SW);
return pte_clear_flags(pte, _PAGE_RW);
}
@@ -316,9 +331,24 @@ static inline pte_t pte_mkexec(pte_t pte)
static inline pte_t pte_mkdirty(pte_t pte)
{
+ pteval_t dirty = (!IS_ENABLED(CONFIG_X86_INTEL_SHADOW_STACK_USER) ||
+ pte_write(pte)) ? _PAGE_DIRTY_HW:_PAGE_DIRTY_SW;
+ return pte_set_flags(pte, dirty | _PAGE_SOFT_DIRTY);
+}
+
+#ifdef CONFIG_ARCH_HAS_SHSTK
+static inline pte_t pte_mkdirty_shstk(pte_t pte)
+{
+ pte = pte_clear_flags(pte, _PAGE_DIRTY_SW);
return pte_set_flags(pte, _PAGE_DIRTY_HW | _PAGE_SOFT_DIRTY);
}
+static inline bool pte_dirty_hw(pte_t pte)
+{
+ return pte_flags(pte) & _PAGE_DIRTY_HW;
+}
+#endif
+
static inline pte_t pte_mkyoung(pte_t pte)
{
return pte_set_flags(pte, _PAGE_ACCESSED);
@@ -326,6 +356,7 @@ static inline pte_t pte_mkyoung(pte_t pte)
static inline pte_t pte_mkwrite(pte_t pte)
{
+ pte = pte_move_flags(pte, _PAGE_DIRTY_SW, _PAGE_DIRTY_HW);
return pte_set_flags(pte, _PAGE_RW);
}
@@ -373,6 +404,20 @@ static inline pmd_t pmd_clear_flags(pmd_t pmd, pmdval_t clear)
return native_make_pmd(v & ~clear);
}
+#if defined(CONFIG_X86_INTEL_SHADOW_STACK_USER)
+static inline pmd_t pmd_move_flags(pmd_t pmd, pmdval_t from, pmdval_t to)
+{
+ if (pmd_flags(pmd) & from)
+ pmd = pmd_set_flags(pmd_clear_flags(pmd, from), to);
+ return pmd;
+}
+#else
+static inline pmd_t pmd_move_flags(pmd_t pmd, pmdval_t from, pmdval_t to)
+{
+ return pmd;
+}
+#endif
+
static inline pmd_t pmd_mkold(pmd_t pmd)
{
return pmd_clear_flags(pmd, _PAGE_ACCESSED);
@@ -380,19 +425,36 @@ static inline pmd_t pmd_mkold(pmd_t pmd)
static inline pmd_t pmd_mkclean(pmd_t pmd)
{
- return pmd_clear_flags(pmd, _PAGE_DIRTY);
+ return pmd_clear_flags(pmd, _PAGE_DIRTY_BITS);
}
static inline pmd_t pmd_wrprotect(pmd_t pmd)
{
+ pmd = pmd_move_flags(pmd, _PAGE_DIRTY_HW, _PAGE_DIRTY_SW);
return pmd_clear_flags(pmd, _PAGE_RW);
}
static inline pmd_t pmd_mkdirty(pmd_t pmd)
{
+ pmdval_t dirty = (!IS_ENABLED(CONFIG_X86_INTEL_SHADOW_STACK_USER) ||
+ (pmd_flags(pmd) & _PAGE_RW)) ?
+ _PAGE_DIRTY_HW:_PAGE_DIRTY_SW;
+ return pmd_set_flags(pmd, dirty | _PAGE_SOFT_DIRTY);
+}
+
+#ifdef CONFIG_ARCH_HAS_SHSTK
+static inline pmd_t pmd_mkdirty_shstk(pmd_t pmd)
+{
+ pmd = pmd_clear_flags(pmd, _PAGE_DIRTY_SW);
return pmd_set_flags(pmd, _PAGE_DIRTY_HW | _PAGE_SOFT_DIRTY);
}
+static inline bool pmd_dirty_hw(pmd_t pmd)
+{
+ return pmd_flags(pmd) & _PAGE_DIRTY_HW;
+}
+#endif
+
static inline pmd_t pmd_mkdevmap(pmd_t pmd)
{
return pmd_set_flags(pmd, _PAGE_DEVMAP);
@@ -410,6 +472,7 @@ static inline pmd_t pmd_mkyoung(pmd_t pmd)
static inline pmd_t pmd_mkwrite(pmd_t pmd)
{
+ pmd = pmd_move_flags(pmd, _PAGE_DIRTY_SW, _PAGE_DIRTY_HW);
return pmd_set_flags(pmd, _PAGE_RW);
}
@@ -427,6 +490,20 @@ static inline pud_t pud_clear_flags(pud_t pud, pudval_t clear)
return native_make_pud(v & ~clear);
}
+#if defined(CONFIG_X86_INTEL_SHADOW_STACK_USER)
+static inline pud_t pud_move_flags(pud_t pud, pudval_t from, pudval_t to)
+{
+ if (pud_flags(pud) & from)
+ pud = pud_set_flags(pud_clear_flags(pud, from), to);
+ return pud;
+}
+#else
+static inline pud_t pud_move_flags(pud_t pud, pudval_t from, pudval_t to)
+{
+ return pud;
+}
+#endif
+
static inline pud_t pud_mkold(pud_t pud)
{
return pud_clear_flags(pud, _PAGE_ACCESSED);
@@ -434,17 +511,22 @@ static inline pud_t pud_mkold(pud_t pud)
static inline pud_t pud_mkclean(pud_t pud)
{
- return pud_clear_flags(pud, _PAGE_DIRTY);
+ return pud_clear_flags(pud, _PAGE_DIRTY_BITS);
}
static inline pud_t pud_wrprotect(pud_t pud)
{
+ pud = pud_move_flags(pud, _PAGE_DIRTY_HW, _PAGE_DIRTY_SW);
return pud_clear_flags(pud, _PAGE_RW);
}
static inline pud_t pud_mkdirty(pud_t pud)
{
- return pud_set_flags(pud, _PAGE_DIRTY_HW | _PAGE_SOFT_DIRTY);
+ pudval_t dirty = (!IS_ENABLED(CONFIG_X86_INTEL_SHADOW_STACK_USER) ||
+ (pud_flags(pud) & _PAGE_RW)) ?
+ _PAGE_DIRTY_HW:_PAGE_DIRTY_SW;
+
+ return pud_set_flags(pud, dirty | _PAGE_SOFT_DIRTY);
}
static inline pud_t pud_mkdevmap(pud_t pud)
@@ -464,6 +546,7 @@ static inline pud_t pud_mkyoung(pud_t pud)
static inline pud_t pud_mkwrite(pud_t pud)
{
+ pud = pud_move_flags(pud, _PAGE_DIRTY_SW, _PAGE_DIRTY_HW);
return pud_set_flags(pud, _PAGE_RW);
}
@@ -595,19 +678,12 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
val &= _PAGE_CHG_MASK;
val |= check_pgprot(newprot) & ~_PAGE_CHG_MASK;
val = flip_protnone_guard(oldval, val, PTE_PFN_MASK);
+ if ((pte_write(pte) && !(pgprot_val(newprot) & _PAGE_RW)))
+ return pte_move_flags(__pte(val), _PAGE_DIRTY_HW,
+ _PAGE_DIRTY_SW);
return __pte(val);
}
-static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
-{
- pmdval_t val = pmd_val(pmd), oldval = val;
-
- val &= _HPAGE_CHG_MASK;
- val |= check_pgprot(newprot) & ~_HPAGE_CHG_MASK;
- val = flip_protnone_guard(oldval, val, PHYSICAL_PMD_PAGE_MASK);
- return __pmd(val);
-}
-
/* mprotect needs to preserve PAT bits when updating vm_page_prot */
#define pgprot_modify pgprot_modify
static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
@@ -1159,6 +1235,19 @@ static inline int pmd_write(pmd_t pmd)
return pmd_flags(pmd) & _PAGE_RW;
}
+static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
+{
+ pmdval_t val = pmd_val(pmd), oldval = val;
+
+ val &= _HPAGE_CHG_MASK;
+ val |= check_pgprot(newprot) & ~_HPAGE_CHG_MASK;
+ val = flip_protnone_guard(oldval, val, PHYSICAL_PMD_PAGE_MASK);
+ if ((pmd_write(pmd) && !(pgprot_val(newprot) & _PAGE_RW)))
+ return pmd_move_flags(__pmd(val), _PAGE_DIRTY_HW,
+ _PAGE_DIRTY_SW);
+ return __pmd(val);
+}
+
#define __HAVE_ARCH_PMDP_HUGE_GET_AND_CLEAR
static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm, unsigned long addr,
pmd_t *pmdp)
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 0657a22d5216..bd17e38d6a36 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -23,6 +23,7 @@
#define _PAGE_BIT_SOFTW2 10 /* " */
#define _PAGE_BIT_SOFTW3 11 /* " */
#define _PAGE_BIT_PAT_LARGE 12 /* On 2MB or 1GB pages */
+#define _PAGE_BIT_SOFTW5 57 /* available for programmer */
#define _PAGE_BIT_SOFTW4 58 /* available for programmer */
#define _PAGE_BIT_PKEY_BIT0 59 /* Protection Keys, bit 1/4 */
#define _PAGE_BIT_PKEY_BIT1 60 /* Protection Keys, bit 2/4 */
@@ -34,6 +35,7 @@
#define _PAGE_BIT_CPA_TEST _PAGE_BIT_SOFTW1
#define _PAGE_BIT_SOFT_DIRTY _PAGE_BIT_SOFTW3 /* software dirty tracking */
#define _PAGE_BIT_DEVMAP _PAGE_BIT_SOFTW4
+#define _PAGE_BIT_DIRTY_SW _PAGE_BIT_SOFTW5 /* was written to */
/* If _PAGE_BIT_PRESENT is clear, we use these: */
/* - if the user mapped it with PROT_NONE; pte_present gives true */
@@ -109,6 +111,21 @@
#define _PAGE_DEVMAP (_AT(pteval_t, 0))
#endif
+/*
+ * _PAGE_DIRTY_HW: set by the processor when a page is written.
+ * _PAGE_DIRTY_SW: a spare bit tracking a written, but now R/O page.
+ * [R/W + _PAGE_DIRTY_HW] <-> [R/O + _PAGE_DIRTY_SW].
+ * _PAGE_SOFT_DIRTY: a spare bit used to track written pages since a time point
+ * set by the system admin; see Documentation/admin-guide/mm/soft-dirty.rst.
+ */
+#if defined(CONFIG_X86_INTEL_SHADOW_STACK_USER)
+#define _PAGE_DIRTY_SW (_AT(pteval_t, 1) << _PAGE_BIT_DIRTY_SW)
+#else
+#define _PAGE_DIRTY_SW (_AT(pteval_t, 0))
+#endif
+
+#define _PAGE_DIRTY_BITS (_PAGE_DIRTY_HW | _PAGE_DIRTY_SW)
+
#define _PAGE_PROTNONE (_AT(pteval_t, 1) << _PAGE_BIT_PROTNONE)
#define _PAGE_TABLE_NOENC (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |\
@@ -122,9 +139,9 @@
* instance, and is *not* included in this mask since
* pte_modify() does modify it.
*/
-#define _PAGE_CHG_MASK (PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT | \
+#define _PAGE_CHG_MASK (PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT | \
_PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY_HW | \
- _PAGE_SOFT_DIRTY)
+ _PAGE_DIRTY_SW | _PAGE_SOFT_DIRTY)
#define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
/*
--
2.17.1
