ARM: move signal handlers into a vdso-like page

Move the signal handlers into a VDSO page rather than keeping them in
the vectors page.  This allows us to place them randomly within this
page, and also map the page at a random location within userspace
further protecting these code fragments from ROP attacks.  The new
VDSO page is also poisoned in the same way as the vector page.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 37 insertions, 3 deletions

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index d3ca4f6915af..566d0d71a1e7 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -428,8 +428,8 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 #ifdef CONFIG_MMU
 /*
  * The vectors page is always readable from user space for the
- * atomic helpers and the signal restart code. Insert it into the
- * gate_vma so that it is visible through ptrace and /proc/<pid>/mem.
+ * atomic helpers. Insert it into the gate_vma so that it is visible
+ * through ptrace and /proc/<pid>/mem.
  */
 static struct vm_area_struct gate_vma = {
 	.vm_start	= 0xffff0000,
@@ -461,6 +461,40 @@ int in_gate_area_no_mm(unsigned long addr)
 
 const char *arch_vma_name(struct vm_area_struct *vma)
 {
-	return (vma == &gate_vma) ? "[vectors]" : NULL;
+	return (vma == &gate_vma) ? "[vectors]" :
+		(vma->vm_mm && vma->vm_start == vma->vm_mm->context.sigpage) ?
+		 "[sigpage]" : NULL;
+}
+
+extern struct page *get_signal_page(void);
+
+int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
+{
+	struct mm_struct *mm = current->mm;
+	struct page *page;
+	unsigned long addr;
+	int ret;
+
+	page = get_signal_page();
+	if (!page)
+		return -ENOMEM;
+
+	down_write(&mm->mmap_sem);
+	addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
+	if (IS_ERR_VALUE(addr)) {
+		ret = addr;
+		goto up_fail;
+	}
+
+	ret = install_special_mapping(mm, addr, PAGE_SIZE,
+		VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
+		&page);
+
+	if (ret == 0)
+		mm->context.sigpage = addr;
+
+ up_fail:
+	up_write(&mm->mmap_sem);
+	return ret;
 }
 #endif