arm64: mm: Introduce PTE_WRITE

We have the following means for encoding writable or dirty ptes:

                                PTE_DIRTY       PTE_RDONLY
!pte_dirty && !pte_write        0               1
!pte_dirty && pte_write         0               1
pte_dirty && !pte_write         1               1
pte_dirty && pte_write          1               0

So we can't distinguish between writable clean ptes and read only
ptes. This can cause problems with ptes being incorrectly flagged as
read only when they are writable but not dirty.

This patch introduces a new software bit PTE_WRITE which allows us to
correctly identify writable ptes. PTE_RDONLY is now only clear for
valid ptes where a page is both writable and dirty.

Signed-off-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 27c78395ae7610abfbbd89e62db6ae7209d5c086..b524dcd17243d712b4d461cf77d4dd56ed04c8bb 100644 (file)
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -28,7 +28,7 @@
 #define PTE_FILE               (_AT(pteval_t, 1) << 2) /* only when !pte_present() */
 #define PTE_DIRTY              (_AT(pteval_t, 1) << 55)
 #define PTE_SPECIAL            (_AT(pteval_t, 1) << 56)
-                               /* bit 57 for PMD_SECT_SPLITTING */
+#define PTE_WRITE              (_AT(pteval_t, 1) << 57)
 #define PTE_PROT_NONE          (_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
 
 /*
@@ -67,15 +67,15 @@ extern pgprot_t pgprot_default;
 
 #define _MOD_PROT(p, b)                __pgprot_modify(p, 0, b)
 
-#define PAGE_NONE              __pgprot_modify(pgprot_default, PTE_TYPE_MASK, PTE_PROT_NONE | PTE_RDONLY | PTE_PXN | PTE_UXN)
-#define PAGE_SHARED            _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
-#define PAGE_SHARED_EXEC       _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN)
-#define PAGE_COPY              _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define PAGE_COPY_EXEC         _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
-#define PAGE_READONLY          _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define PAGE_READONLY_EXEC     _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
-#define PAGE_KERNEL            _MOD_PROT(pgprot_default, PTE_PXN | PTE_UXN | PTE_DIRTY)
-#define PAGE_KERNEL_EXEC       _MOD_PROT(pgprot_default, PTE_UXN | PTE_DIRTY)
+#define PAGE_NONE              __pgprot_modify(pgprot_default, PTE_TYPE_MASK, PTE_PROT_NONE | PTE_PXN | PTE_UXN)
+#define PAGE_SHARED            _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_WRITE)
+#define PAGE_SHARED_EXEC       _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_WRITE)
+#define PAGE_COPY              _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define PAGE_COPY_EXEC         _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN)
+#define PAGE_READONLY          _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define PAGE_READONLY_EXEC     _MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN)
+#define PAGE_KERNEL            _MOD_PROT(pgprot_default, PTE_PXN | PTE_UXN | PTE_DIRTY | PTE_WRITE)
+#define PAGE_KERNEL_EXEC       _MOD_PROT(pgprot_default, PTE_UXN | PTE_DIRTY | PTE_WRITE)
 
 #define PAGE_HYP               _MOD_PROT(pgprot_default, PTE_HYP)
 #define PAGE_HYP_DEVICE                __pgprot(PROT_DEVICE_nGnRE | PTE_HYP)
@@ -83,13 +83,13 @@ extern pgprot_t pgprot_default;
 #define PAGE_S2                        __pgprot_modify(pgprot_default, PTE_S2_MEMATTR_MASK, PTE_S2_MEMATTR(MT_S2_NORMAL) | PTE_S2_RDONLY)
 #define PAGE_S2_DEVICE         __pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_DEVICE_nGnRE) | PTE_S2_RDWR | PTE_UXN)
 
-#define __PAGE_NONE            __pgprot(((_PAGE_DEFAULT) & ~PTE_TYPE_MASK) | PTE_PROT_NONE | PTE_RDONLY | PTE_PXN | PTE_UXN)
-#define __PAGE_SHARED          __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
-#define __PAGE_SHARED_EXEC     __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
-#define __PAGE_COPY            __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define __PAGE_COPY_EXEC       __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
-#define __PAGE_READONLY                __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define __PAGE_READONLY_EXEC   __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
+#define __PAGE_NONE            __pgprot(((_PAGE_DEFAULT) & ~PTE_TYPE_MASK) | PTE_PROT_NONE | PTE_PXN | PTE_UXN)
+#define __PAGE_SHARED          __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_WRITE)
+#define __PAGE_SHARED_EXEC     __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_WRITE)
+#define __PAGE_COPY            __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define __PAGE_COPY_EXEC       __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
+#define __PAGE_READONLY                __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define __PAGE_READONLY_EXEC   __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
 
 #endif /* __ASSEMBLY__ */
 
@@ -140,7 +140,7 @@ extern struct page *empty_zero_page;
 #define pte_dirty(pte)         (pte_val(pte) & PTE_DIRTY)
 #define pte_young(pte)         (pte_val(pte) & PTE_AF)
 #define pte_special(pte)       (pte_val(pte) & PTE_SPECIAL)
-#define pte_write(pte)         (!(pte_val(pte) & PTE_RDONLY))
+#define pte_write(pte)         (pte_val(pte) & PTE_WRITE)
 #define pte_exec(pte)          (!(pte_val(pte) & PTE_UXN))
 
 #define pte_valid_user(pte) \
@@ -148,13 +148,13 @@ extern struct page *empty_zero_page;
 
 static inline pte_t pte_wrprotect(pte_t pte)
 {
-       pte_val(pte) |= PTE_RDONLY;
+       pte_val(pte) &= ~PTE_WRITE;
        return pte;
 }
 
 static inline pte_t pte_mkwrite(pte_t pte)
 {
-       pte_val(pte) &= ~PTE_RDONLY;
+       pte_val(pte) |= PTE_WRITE;
        return pte;
 }
 
@@ -201,8 +201,10 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
        if (pte_valid_user(pte)) {
                if (pte_exec(pte))
                        __sync_icache_dcache(pte, addr);
-               if (!pte_dirty(pte))
-                       pte = pte_wrprotect(pte);
+               if (pte_dirty(pte) && pte_write(pte))
+                       pte_val(pte) &= ~PTE_RDONLY;
+               else
+                       pte_val(pte) |= PTE_RDONLY;
        }
 
        set_pte(ptep, pte);
@@ -376,7 +378,7 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
        const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
-                             PTE_PROT_NONE | PTE_VALID;
+                             PTE_PROT_NONE | PTE_VALID | PTE_WRITE;
        pte_val(pte) = (pte_val(pte) & ~mask) | (pgprot_val(newprot) & mask);
        return pte;
 }