x86/fpu: Use copy_xstate_to_uabi_buf() in xfpregs_get()

Use the new functionality of copy_xstate_to_uabi_buf() to retrieve the
FX state when XSAVE* is in use. This avoids overwriting the FPU state
buffer with fpstate_sanitize_xstate() which is error prone and duplicated
code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121452.901736860@linutronix.de

arch/x86/kernel/fpu/regset.c

@@ -33,13 +33,18 @@ int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
 {
 	struct fpu *fpu = &target->thread.fpu;
 
-	if (!boot_cpu_has(X86_FEATURE_FXSR))
+	if (!cpu_feature_enabled(X86_FEATURE_FXSR))
 		return -ENODEV;
 
 	fpu__prepare_read(fpu);
-	fpstate_sanitize_xstate(fpu);
 
-	return membuf_write(&to, &fpu->state.fxsave, sizeof(struct fxregs_state));
+	if (!use_xsave()) {
+		return membuf_write(&to, &fpu->state.fxsave,
+				    sizeof(fpu->state.fxsave));
+	}
+
+	copy_xstate_to_uabi_buf(to, &fpu->state.xsave, XSTATE_COPY_FX);
+	return 0;
 }
 
 int xfpregs_set(struct task_struct *target, const struct user_regset *regset,