s390/vdso: add minimal compat vdso

Add a small vdso for 31 bit compat application that provides
trampolines for calls to sigreturn,rt_sigreturn,syscall_restart.
This is requird for moving these syscalls away from the signal
frame to the vdso. Note that this patch effectively disables
CONFIG_COMPAT when using clang to compile the kernel. clang
doesn't support 31 bit mode.

We want to redirect sigreturn and restart_syscall to the vdso. However,
the kernel cannot parse the ELF vdso file, so we need to generate header
files which contain the offsets of the syscall instructions in the vdso
page.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 32 insertions, 16 deletions

diff --git a/arch/s390/kernel/vdso.c b/arch/s390/kernel/vdso.c
index f786246e621a..99694260cac9 100644
--- a/arch/s390/kernel/vdso.c
+++ b/arch/s390/kernel/vdso.c
@@ -20,7 +20,7 @@
 #include <asm/vdso.h>
 
 extern char vdso64_start[], vdso64_end[];
-static unsigned int vdso_pages;
+extern char vdso32_start[], vdso32_end[];
 
 static struct vm_special_mapping vvar_mapping;
 
@@ -143,7 +143,12 @@ static struct vm_special_mapping vvar_mapping = {
 	.fault = vvar_fault,
 };
 
-static struct vm_special_mapping vdso_mapping = {
+static struct vm_special_mapping vdso64_mapping = {
+	.name = "[vdso]",
+	.mremap = vdso_mremap,
+};
+
+static struct vm_special_mapping vdso32_mapping = {
 	.name = "[vdso]",
 	.mremap = vdso_mremap,
 };
@@ -159,16 +164,22 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
 	unsigned long vdso_text_len, vdso_mapping_len;
 	unsigned long vvar_start, vdso_text_start;
+	struct vm_special_mapping *vdso_mapping;
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
 	int rc;
 
 	BUILD_BUG_ON(VVAR_NR_PAGES != __VVAR_PAGES);
-	if (is_compat_task())
-		return 0;
 	if (mmap_write_lock_killable(mm))
 		return -EINTR;
-	vdso_text_len = vdso_pages << PAGE_SHIFT;
+
+	if (is_compat_task()) {
+		vdso_text_len = vdso32_end - vdso32_start;
+		vdso_mapping = &vdso32_mapping;
+	} else {
+		vdso_text_len = vdso64_end - vdso64_start;
+		vdso_mapping = &vdso64_mapping;
+	}
 	vdso_mapping_len = vdso_text_len + VVAR_NR_PAGES * PAGE_SIZE;
 	vvar_start = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0);
 	rc = vvar_start;
@@ -186,7 +197,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 	vma = _install_special_mapping(mm, vdso_text_start, vdso_text_len,
 				       VM_READ|VM_EXEC|
 				       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
-				       &vdso_mapping);
+				       vdso_mapping);
 	if (IS_ERR(vma)) {
 		do_munmap(mm, vvar_start, PAGE_SIZE, NULL);
 		rc = PTR_ERR(vma);
@@ -199,20 +210,25 @@ out:
 	return rc;
 }
 
-static int __init vdso_init(void)
+static struct page ** __init vdso_setup_pages(void *start, void *end)
 {
-	struct page **pages;
+	int pages = (end - start) >> PAGE_SHIFT;
+	struct page **pagelist;
 	int i;
 
-	vdso_pages = (vdso64_end - vdso64_start) >> PAGE_SHIFT;
-	pages = kcalloc(vdso_pages + 1, sizeof(struct page *), GFP_KERNEL);
-	if (!pages)
-		panic("failed to allocate VDSO pages");
+	pagelist = kcalloc(pages + 1, sizeof(struct page *), GFP_KERNEL);
+	if (!pagelist)
+		panic("%s: Cannot allocate page list for VDSO", __func__);
+	for (i = 0; i < pages; i++)
+		pagelist[i] = virt_to_page(start + i * PAGE_SIZE);
+	return pagelist;
+}
 
-	for (i = 0; i < vdso_pages; i++)
-		pages[i] = virt_to_page(vdso64_start + i * PAGE_SIZE);
-	pages[vdso_pages] = NULL;
-	vdso_mapping.pages = pages;
+static int __init vdso_init(void)
+{
+	vdso64_mapping.pages = vdso_setup_pages(vdso64_start, vdso64_end);
+	if (IS_ENABLED(CONFIG_COMPAT))
+		vdso32_mapping.pages = vdso_setup_pages(vdso32_start, vdso32_end);
 	return 0;
 }
 arch_initcall(vdso_init);