[src/trunk]: src/sys/arch/x86/x86 Clarify and extend the fix for the AMD FPU ...

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

details:   https://anonhg.NetBSD.org/src/rev/8ac8da14f20e
branches:  trunk
changeset: 319270:8ac8da14f20e
user:      maxv <maxv%NetBSD.org@localhost>
date:      Wed May 23 10:00:27 2018 +0000

description:
Clarify and extend the fix for the AMD FPU leaks. We were clearing the x87
state only on FXRSTOR, but the same problem exists on XRSTOR, so clear the
state there too.

diffstat:

 sys/arch/x86/x86/fpu.c |  41 +++++++++++++++++++++++++++--------------
 1 files changed, 27 insertions(+), 14 deletions(-)

diffs (80 lines):

diff -r 70f578b84636 -r 8ac8da14f20e sys/arch/x86/x86/fpu.c
--- a/sys/arch/x86/x86/fpu.c    Wed May 23 09:52:27 2018 +0000
+++ b/sys/arch/x86/x86/fpu.c    Wed May 23 10:00:27 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: fpu.c,v 1.30 2018/05/23 07:45:35 maxv Exp $    */
+/*     $NetBSD: fpu.c,v 1.31 2018/05/23 10:00:27 maxv Exp $    */
 
 /*
  * Copyright (c) 2008 The NetBSD Foundation, Inc.  All
@@ -96,7 +96,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: fpu.c,v 1.30 2018/05/23 07:45:35 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: fpu.c,v 1.31 2018/05/23 10:00:27 maxv Exp $");
 
 #include "opt_multiprocessor.h"
 
@@ -109,6 +109,8 @@
 #include <sys/kernel.h>
 
 #include <machine/cpu.h>
+#include <machine/cpuvar.h>
+#include <machine/cputypes.h>
 #include <machine/intr.h>
 #include <machine/cpufunc.h>
 #include <machine/pcb.h>
@@ -337,6 +339,25 @@
        (*curlwp->l_proc->p_emul->e_trapsignal)(curlwp, &ksi);
 }
 
+static void
+fpu_clear_amd(void)
+{
+       /*
+        * AMD FPUs do not restore FIP, FDP, and FOP on fxrstor and xrstor
+        * when FSW.ES=0, leaking other threads' execution history.
+        *
+        * Clear them manually by loading a zero (fldummy). We do this
+        * unconditionally, regardless of FSW.ES.
+        *
+        * Before that, clear the ES bit in the x87 status word if it is
+        * currently set, in order to avoid causing a fault in the
+        * upcoming load.
+        */
+       if (fngetsw() & 0x80)
+               fnclex();
+       fldummy();
+}
+
 /*
  * Implement device not available (DNA) exception
  *
@@ -409,22 +430,14 @@
                frstor(&pcb->pcb_savefpu);
                break;
        case FPU_SAVE_FXSAVE:
-               /*
-                * AMD FPU's do not restore FIP, FDP, and FOP on
-                * fxrstor, leaking other process's execution history.
-                * Clear them manually by loading a zero.
-                *
-                * Clear the ES bit in the x87 status word if it is
-                * currently set, in order to avoid causing a fault
-                * in the upcoming load.
-                */
-               if (fngetsw() & 0x80)
-                       fnclex();
-               fldummy();
+               if (cpu_vendor == CPUVENDOR_AMD)
+                       fpu_clear_amd();
                fxrstor(&pcb->pcb_savefpu);
                break;
        case FPU_SAVE_XSAVE:
        case FPU_SAVE_XSAVEOPT:
+               if (cpu_vendor == CPUVENDOR_AMD)
+                       fpu_clear_amd();
                xrstor(&pcb->pcb_savefpu, x86_xsave_features);
                break;
        }