arm64: vdso: move data page before code pages

Andy pointed out that binutils generates additional sections in the vdso
image (e.g. section string table) which, if our .text section gets big
enough, could cross a page boundary and end up screwing up the location
where the kernel expects to put the data page.

This patch solves the issue in the same manner as x86_32, by moving the
data page before the code pages.

Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/vdso.c

@@ -121,8 +121,8 @@ static int __init vdso_init(void)
 	}
 
 	vdso_pages = (&vdso_end - &vdso_start) >> PAGE_SHIFT;
-	pr_info("vdso: %ld pages (%ld code, %ld data) at base %p\n",
-		vdso_pages + 1, vdso_pages, 1L, &vdso_start);
+	pr_info("vdso: %ld pages (%ld code @ %p, %ld data @ %p)\n",
+		vdso_pages + 1, vdso_pages, &vdso_start, 1L, vdso_data);
 
 	/* Allocate the vDSO pagelist, plus a page for the data. */
 	vdso_pagelist = kcalloc(vdso_pages + 1, sizeof(struct page *),
@@ -130,22 +130,22 @@ static int __init vdso_init(void)
 	if (vdso_pagelist == NULL)
 		return -ENOMEM;
 
+	/* Grab the vDSO data page. */
+	vdso_pagelist[0] = virt_to_page(vdso_data);
+
 	/* Grab the vDSO code pages. */
 	for (i = 0; i < vdso_pages; i++)
-		vdso_pagelist[i] = virt_to_page(&vdso_start + i * PAGE_SIZE);
-
-	/* Grab the vDSO data page. */
-	vdso_pagelist[i] = virt_to_page(vdso_data);
+		vdso_pagelist[i + 1] = virt_to_page(&vdso_start + i * PAGE_SIZE);
 
 	/* Populate the special mapping structures */
 	vdso_spec[0] = (struct vm_special_mapping) {
-		.name	= "[vdso]",
+		.name	= "[vvar]",
 		.pages	= vdso_pagelist,
 	};
 
 	vdso_spec[1] = (struct vm_special_mapping) {
-		.name	= "[vvar]",
-		.pages	= vdso_pagelist + vdso_pages,
+		.name	= "[vdso]",
+		.pages	= &vdso_pagelist[1],
 	};
 
 	return 0;
@@ -169,22 +169,22 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
 		ret = ERR_PTR(vdso_base);
 		goto up_fail;
 	}
-	mm->context.vdso = (void *)vdso_base;
-
-	ret = _install_special_mapping(mm, vdso_base, vdso_text_len,
-				       VM_READ|VM_EXEC|
-				       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
+	ret = _install_special_mapping(mm, vdso_base, PAGE_SIZE,
+				       VM_READ|VM_MAYREAD,
 				       &vdso_spec[0]);
 	if (IS_ERR(ret))
 		goto up_fail;
 
-	vdso_base += vdso_text_len;
-	ret = _install_special_mapping(mm, vdso_base, PAGE_SIZE,
-				       VM_READ|VM_MAYREAD,
+	vdso_base += PAGE_SIZE;
+	mm->context.vdso = (void *)vdso_base;
+	ret = _install_special_mapping(mm, vdso_base, vdso_text_len,
+				       VM_READ|VM_EXEC|
+				       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 				       &vdso_spec[1]);
 	if (IS_ERR(ret))
 		goto up_fail;
 
+
 	up_write(&mm->mmap_sem);
 	return 0;
 

arch/arm64/kernel/vdso/vdso.lds.S

@@ -28,6 +28,7 @@ OUTPUT_ARCH(aarch64)
 
 SECTIONS
 {
+	PROVIDE(_vdso_data = . - PAGE_SIZE);
 	. = VDSO_LBASE + SIZEOF_HEADERS;
 
 	.hash		: { *(.hash) }			:text
@@ -57,9 +58,6 @@ SECTIONS
 	_end = .;
 	PROVIDE(end = .);
 
-	. = ALIGN(PAGE_SIZE);
-	PROVIDE(_vdso_data = .);
-
 	/DISCARD/	: {
 		*(.note.GNU-stack)
 		*(.data .data.* .gnu.linkonce.d.* .sdata*)