um: support some of ARCH_HAS_SET_MEMORY

For now, only support set_memory_ro()/rw() which we need for
the stack protection in the next patch.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/Kconfig

@@ -15,6 +15,7 @@ config UML
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DEBUG_BUGVERBOSE
 	select NO_DMA
+	select ARCH_HAS_SET_MEMORY
 	select GENERIC_IRQ_SHOW
 	select GENERIC_CPU_DEVICES
 	select GENERIC_CLOCKEVENTS

arch/um/include/asm/pgtable.h

@@ -55,12 +55,15 @@ extern unsigned long end_iomem;
 #define _PAGE_CHG_MASK	(PAGE_MASK | _PAGE_ACCESSED | _PAGE_DIRTY)
 #define __PAGE_KERNEL_EXEC                                              \
 	 (_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED)
+#define __PAGE_KERNEL_RO						\
+	 (_PAGE_PRESENT | _PAGE_DIRTY | _PAGE_ACCESSED)
 #define PAGE_NONE	__pgprot(_PAGE_PROTNONE | _PAGE_ACCESSED)
 #define PAGE_SHARED	__pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | _PAGE_ACCESSED)
 #define PAGE_COPY	__pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED)
 #define PAGE_READONLY	__pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED)
 #define PAGE_KERNEL	__pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED)
 #define PAGE_KERNEL_EXEC	__pgprot(__PAGE_KERNEL_EXEC)
+#define PAGE_KERNEL_RO		__pgprot(__PAGE_KERNEL_RO)
 
 /*
  * The i386 can't do page protection for execute, and considers that the same

arch/um/include/asm/set_memory.h

+#include <asm-generic/set_memory.h>

arch/um/kernel/tlb.c

@@ -608,3 +608,57 @@ void force_flush_all(void)
 		vma = vma->vm_next;
 	}
 }
+
+struct page_change_data {
+	unsigned int set_mask, clear_mask;
+};
+
+static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
+{
+	struct page_change_data *cdata = data;
+	pte_t pte = READ_ONCE(*ptep);
+
+	pte_clear_bits(pte, cdata->clear_mask);
+	pte_set_bits(pte, cdata->set_mask);
+
+	set_pte(ptep, pte);
+	return 0;
+}
+
+static int change_memory(unsigned long start, unsigned long pages,
+			 unsigned int set_mask, unsigned int clear_mask)
+{
+	unsigned long size = pages * PAGE_SIZE;
+	struct page_change_data data;
+	int ret;
+
+	data.set_mask = set_mask;
+	data.clear_mask = clear_mask;
+
+	ret = apply_to_page_range(&init_mm, start, size, change_page_range,
+				  &data);
+
+	flush_tlb_kernel_range(start, start + size);
+
+	return ret;
+}
+
+int set_memory_ro(unsigned long addr, int numpages)
+{
+	return change_memory(addr, numpages, 0, _PAGE_RW);
+}
+
+int set_memory_rw(unsigned long addr, int numpages)
+{
+	return change_memory(addr, numpages, _PAGE_RW, 0);
+}
+
+int set_memory_nx(unsigned long addr, int numpages)
+{
+	return -EOPNOTSUPP;
+}
+
+int set_memory_x(unsigned long addr, int numpages)
+{
+	return -EOPNOTSUPP;
+}