On 7/22/2021 2:05 PM, Dave Hansen wrote:
On 7/22/21 1:52 PM, Yu-cheng Yu wrote:
+ if (!stack_size)
+ stack_size = min_t(unsigned long long, rlimit(RLIMIT_STACK), SZ_4G);
+
+ if (!shstk->size)
+ return 0;
+
+ /*
+ * For CLONE_VM, except vfork, the child needs a separate shadow
+ * stack.
+ */
+ if ((clone_flags & (CLONE_VFORK | CLONE_VM)) != CLONE_VM)
+ return 0;
+
+ /*
+ * This is in clone() syscall and fpu__copy() already copies xstates
+ * from the parent. If get_xsave_addr() returns null, then XFEATURE_
+ * CET_USER is still in init state, which certainly is an error.
+ */
+ state = get_xsave_addr(&tsk->thread.fpu.state.xsave, XFEATURE_CET_USER);
+ if (!state)
+ return -EINVAL;
I don't care much for that comment.
This code is meant to copy shadow stack config information into children
when it is already enabled. We *just* checked for that above in the
"shstk->size" check. The fact that this is called from clone() is
irrelevant. The shadow stack enabling status *is*.
I think I'd rather this be more along the lines of:
/*
* 'tsk' is configured with a shadow stack and the fpu.state is
* up to date since it was just copied from the parent. There
* must be a valid non-init CET state location in the buffer.
*/
There is also a strong enough assumption violation that I'd probably
WARN() in addition to returning -EINVAL.
Yes, I will update the comment and put in the WARN().
Thanks,
Yu-cheng
