[RFC PATCH 3/3] Prevent user from writing to IBT bitmap.

[Yu-cheng Yu]

The IBT bitmap is visiable from user-mode, but not writable.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>

---
 arch/x86/mm/fault.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 59f4f66e4f2e..231196abb62e 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1454,6 +1454,13 @@ void do_user_addr_fault(struct pt_regs *regs,
 	 * we can handle it..
 	 */
 good_area:
+#define USER_MODE_WRITE (FAULT_FLAG_WRITE | FAULT_FLAG_USER)
+	if (((flags & USER_MODE_WRITE)  == USER_MODE_WRITE) &&
+	    (vma->vm_flags & VM_IBT)) {
+		bad_area_access_error(regs, hw_error_code, address, vma);
+		return;
+	}
+
 	if (unlikely(access_error(hw_error_code, vma))) {
 		bad_area_access_error(regs, hw_error_code, address, vma);
 		return;
-- 
2.17.1