Introduce PTRACE_REGS_ALIGN, and on x86, enforce a 16-byte alignment,…

… due

to fpregs having fxsave which requires 16-byte alignment.

Reported-by: syzbot+f44d47e617ebf7fda081@syzkaller.appspotmail.com

sys/arch/amd64/include/ptrace.h

@@ -1,4 +1,4 @@
-/*	$NetBSD: ptrace.h,v 1.21 2020/01/08 17:21:38 mgorny Exp $	*/
+/*	$NetBSD: ptrace.h,v 1.22 2020/05/30 08:41:22 maxv Exp $	*/
 
 /*
  * Copyright (c) 1993 Christopher G. Demetriou
@@ -101,6 +101,12 @@
 int process_machdep_doxstate(struct lwp *, struct lwp *, struct uio *);
 int process_machdep_validfpu(struct proc *);
 
+/*
+ * The fpregs structure contains an fxsave area, which must have 16-byte
+ * alignment.
+ */
+#define PTRACE_REGS_ALIGN __aligned(16)
+
 #include <sys/module_hook.h>
 MODULE_HOOK(netbsd32_process_doxmmregs_hook, int,
     (struct lwp *, struct lwp *, void *, bool));

sys/arch/i386/include/ptrace.h

@@ -1,4 +1,4 @@
-/*	$NetBSD: ptrace.h,v 1.25 2020/01/09 10:46:31 kamil Exp $	*/
+/*	$NetBSD: ptrace.h,v 1.26 2020/05/30 08:41:23 maxv Exp $	*/
 
 /*
  * Copyright (c) 2001 Wasabi Systems, Inc.
@@ -187,6 +187,12 @@ int	procfs_machdep_doxmmregs(struct lwp *, struct lwp *,
 	    struct pfsnode *, struct uio *);
 int	procfs_machdep_validxmmregs(struct lwp *, struct mount *);
 
+/*
+ * The fpregs structure contains an fxsave area, which must have 16-byte
+ * alignment.
+ */
+#define PTRACE_REGS_ALIGN __aligned(16)
+
 #endif /* _KERNEL */
 
 #endif /* _I386_PTRACE_H_ */

sys/kern/sys_ptrace_common.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: sys_ptrace_common.c,v 1.82 2020/05/26 23:08:56 kamil Exp $	*/
+/*	$NetBSD: sys_ptrace_common.c,v 1.83 2020/05/30 08:41:22 maxv Exp $	*/
 
 /*-
  * Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
@@ -118,7 +118,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_ptrace_common.c,v 1.82 2020/05/26 23:08:56 kamil Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_ptrace_common.c,v 1.83 2020/05/30 08:41:22 maxv Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_ptrace.h"
@@ -214,6 +214,10 @@ static kcondvar_t ptrace_cv;
 # define PT_REGISTERS
 #endif
 
+#ifndef PTRACE_REGS_ALIGN
+#define PTRACE_REGS_ALIGN /* nothing */
+#endif
+
 static int
 ptrace_listener_cb(kauth_cred_t cred, kauth_action_t action, void *cookie,
     void *arg0, void *arg1, void *arg2, void *arg3)
@@ -1591,7 +1595,7 @@ static int
 proc_regio(struct lwp *l, struct uio *uio, size_t ks, regrfunc_t r,
     regwfunc_t w)
 {
-	char buf[1024];
+	char buf[1024] PTRACE_REGS_ALIGN;
 	int error;
 	char *kv;
 	size_t kl;