An attacker could modify the shadow stack, it's just rather difficult to find where it's randomly placed and would require arbitrary read/write capabilities. Th

An attacker could modify the shadow stack, it's just rather difficult to find where it's randomly placed and would require arbitrary read/write capabilities. The kernel zeros out the register used to write to the shadow stack as soon as possible after use. It's not impossible to defeat, but does raise the bar significantly. I encourage you to read the commit message of shadow call stack kernel patches, which as another commenter notes is only backwards edge protection; CFI is forwards edge protection.