s390/vdso: put vdso datapage in a separate vma

Add a separate "[vvar]" mapping for the vdso datapage, since it
doesn't need to be executable or COW-able.

This is actually the s390 implementation of commit 871549385278
("arm64: vdso: put vdso datapage in a separate vma")

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/kernel/vdso.c b/arch/s390/kernel/vdso.c
index 86e7a39..968b263 100644 (file)
--- a/arch/s390/kernel/vdso.c
+++ b/arch/s390/kernel/vdso.c
@@ -40,6 +40,14 @@ static int __init vdso_setup(char *str)
 }
 __setup("vdso=", vdso_setup);
 
+static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
+                            struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+       if (vmf->pgoff == 0)
+               return vmf_insert_pfn(vma, vmf->address, virt_to_pfn(vdso_data));
+       return VM_FAULT_SIGBUS;
+}
+
 static int vdso_mremap(const struct vm_special_mapping *sm,
                       struct vm_area_struct *vma)
 {
@@ -47,6 +55,11 @@ static int vdso_mremap(const struct vm_special_mapping *sm,
        return 0;
 }
 
+static struct vm_special_mapping vvar_mapping = {
+       .name = "[vvar]",
+       .fault = vvar_fault,
+};
+
 static struct vm_special_mapping vdso_mapping = {
        .name = "[vdso]",
        .mremap = vdso_mremap,
@@ -61,38 +74,41 @@ early_initcall(vdso_getcpu_init); /* Must be called before SMP init */
 
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
+       unsigned long addr, vdso_text_start, vdso_text_len, vdso_mapping_len;
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
-       unsigned long vdso_base;
        int rc;
 
        if (!vdso_enabled || is_compat_task())
                return 0;
        if (mmap_write_lock_killable(mm))
                return -EINTR;
-       vdso_base = get_unmapped_area(NULL, 0, vdso_pages << PAGE_SHIFT, 0, 0);
-       rc = vdso_base;
-       if (IS_ERR_VALUE(vdso_base))
+       vdso_text_len = vdso_pages << PAGE_SHIFT;
+       vdso_mapping_len = vdso_text_len + PAGE_SIZE;
+       addr = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0);
+       rc = addr;
+       if (IS_ERR_VALUE(addr))
                goto out;
-       /*
-        * our vma flags don't have VM_WRITE so by default, the process
-        * isn't allowed to write those pages.
-        * gdb can break that with ptrace interface, and thus trigger COW
-        * on those pages but it's then your responsibility to never do that
-        * on the "data" page of the vDSO or you'll stop getting kernel
-        * updates and your nice userland gettimeofday will be totally dead.
-        * It's fine to use that for setting breakpoints in the vDSO code
-        * pages though.
-        */
-       vma = _install_special_mapping(mm, vdso_base, vdso_pages << PAGE_SHIFT,
+       /* VM_MAYWRITE for COW so gdb can set breakpoints */
+       vdso_text_start = addr;
+       vma = _install_special_mapping(mm, addr, vdso_text_len,
                                       VM_READ|VM_EXEC|
                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
                                       &vdso_mapping);
        rc = PTR_ERR(vma);
        if (IS_ERR(vma))
                goto out;
-       current->mm->context.vdso_base = vdso_base;
-       rc = 0;
+       addr += vdso_text_len;
+       vma = _install_special_mapping(mm, addr, PAGE_SIZE,
+                                      VM_READ|VM_MAYREAD|VM_PFNMAP,
+                                      &vvar_mapping);
+       if (IS_ERR(vma)) {
+               do_munmap(mm, vdso_text_start, vdso_text_len, NULL);
+               rc = PTR_ERR(vma);
+       } else {
+               current->mm->context.vdso_base = vdso_text_start;
+               rc = 0;
+       }
 out:
        mmap_write_unlock(mm);
        return rc;
@@ -103,15 +119,14 @@ static int __init vdso_init(void)
        struct page **pages;
        int i;
 
-       vdso_pages = ((vdso64_end - vdso64_start) >> PAGE_SHIFT) + 1;
+       vdso_pages = (vdso64_end - vdso64_start) >> PAGE_SHIFT;
        pages = kcalloc(vdso_pages + 1, sizeof(struct page *), GFP_KERNEL);
        if (!pages) {
                vdso_enabled = 0;
                return -ENOMEM;
        }
-       for (i = 0; i < vdso_pages - 1; i++)
+       for (i = 0; i < vdso_pages; i++)
                pages[i] = virt_to_page(vdso64_start + i * PAGE_SIZE);
-       pages[vdso_pages - 1] = virt_to_page(vdso_data);
        pages[vdso_pages] = NULL;
        vdso_mapping.pages = pages;
        return 0;