[src/trunk]: src/sys/arch/amd64/amd64 Zero out the scratch value in the UTLS ...

[maxv <maxv%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/53c966950c26
branches:  trunk
changeset: 829341:53c966950c26
user:      maxv <maxv%NetBSD.org@localhost>
date:      Fri Jan 26 14:38:46 2018 +0000

description:
Zero out the scratch value in the UTLS page during context switches. We
temporarily put %rax there when processing syscalls, and we wouldn't
want the new lwp to see the %rax value of the previous lwp.

diffstat:

 sys/arch/amd64/amd64/machdep.c |  8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diffs (36 lines):

diff -r 658b68e59fb7 -r 53c966950c26 sys/arch/amd64/amd64/machdep.c
--- a/sys/arch/amd64/amd64/machdep.c    Fri Jan 26 14:10:15 2018 +0000
+++ b/sys/arch/amd64/amd64/machdep.c    Fri Jan 26 14:38:46 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: machdep.c,v 1.295 2018/01/21 11:21:40 maxv Exp $       */
+/*     $NetBSD: machdep.c,v 1.296 2018/01/26 14:38:46 maxv Exp $       */
 
 /*
  * Copyright (c) 1996, 1997, 1998, 2000, 2006, 2007, 2008, 2011
@@ -110,7 +110,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.295 2018/01/21 11:21:40 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.296 2018/01/26 14:38:46 maxv Exp $");
 
 /* #define XENDEBUG_LOW  */
 
@@ -2522,6 +2522,7 @@
 svs_lwp_switch(struct lwp *oldlwp, struct lwp *newlwp)
 {
        struct cpu_info *ci = curcpu();
+       struct svs_utls *utls;
        struct pcb *pcb;
        pt_entry_t *pte;
        uintptr_t rsp0;
@@ -2551,6 +2552,9 @@
        KASSERT((ci->ci_svs_krsp0 % PAGE_SIZE) ==
            (ci->ci_svs_ursp0 % PAGE_SIZE));
 
+       utls = (struct svs_utls *)ci->ci_svs_utls;
+       utls->scratch = 0;
+
        /*
         * Enter the user rsp0. We don't need to flush the TLB here, since
         * the user page tables are not loaded.