arm64/sme: Always exit sme_alloc() early with existing storage

commit dc7eb8755797ed41a0d1b5c0c39df3c8f401b3d9 upstream.

When sme_alloc() is called with existing storage and we are not flushing we
will always allocate new storage, both leaking the existing storage and
corrupting the state. Fix this by separating the checks for flushing and
for existing storage as we do for SVE.

Callers that reallocate (eg, due to changing the vector length) should
call sme_free() themselves.

Fixes: 5d0a8d2fba50 ("arm64/ptrace: Ensure that SME is set up for target when writing SSVE state")
Signed-off-by: Mark Brown <[email protected]>
Cc: <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>
Signed-off-by: Zhaoyang Li <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: broonie

arch/arm64/kernel/fpsimd.c

@@ -1259,8 +1259,10 @@ void fpsimd_release_task(struct task_struct *dead_task)
  */
 void sme_alloc(struct task_struct *task, bool flush)
 {
-	if (task->thread.za_state && flush) {
-		memset(task->thread.za_state, 0, za_state_size(task));
+	if (task->thread.za_state) {
+		if (flush)
+			memset(task->thread.za_state, 0,
+			       za_state_size(task));
 		return;
 	}