On Sat, 2019-06-29 at 16:44 -0700, Andy Lutomirski wrote:

On Fri, Jun 28, 2019 at 12:50 PM Yu-cheng Yu [off-list ref] wrote:

quoted

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

Signed-off-by: Yu-cheng Yu <redacted>

---
 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;
+       }
+

Just make the VMA have VM_WRITE and VM_MAYWRITE clear.  No new code
like this should be required.

Ok, I will work on that.

Thanks,
Yu-cheng