On 5/17/2021 5:14 PM, Eugene Syromiatnikov wrote:

On Mon, May 17, 2021 at 01:55:01PM -0700, Yu, Yu-cheng wrote:

quoted

On 5/17/2021 12:45 AM, Borislav Petkov wrote:

quoted

On Tue, Apr 27, 2021 at 01:43:09PM -0700, Yu-cheng Yu wrote:

quoted

+static inline int write_user_shstk_32(u32 __user *addr, u32 val)
+{
+	WARN_ONCE(1, "%s used but not supported.\n", __func__);
+	return -EFAULT;
+}
+#endif

What is that supposed to catch? Any concrete (mis-)use cases?

If 32-bit apps are not supported, there should be no need of 32-bit shadow
stack write, otherwise there is a bug.

Speaking of which, I wonder what would happen if a 64-bit process makes
a 32-bit system call (using int 0x80, for example), and gets a signal.

Yes, that's right.  Thanks!  I should have said, if neither IA32 nor X32 
is supported.

Yu-cheng