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From: "Jan Beulich" <JBeulich@suse.com>
To: xen-devel <xen-devel@lists.xenproject.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: [PATCH 2/2] x86/HVM: re-order operations in hvm_ud_intercept()
Date: Wed, 08 Jun 2016 07:43:39 -0600	[thread overview]
Message-ID: <57583D2B02000078000F31CE@prv-mh.provo.novell.com> (raw)
In-Reply-To: <57583B4E02000078000F3198@prv-mh.provo.novell.com>

[-- Attachment #1: Type: text/plain, Size: 2020 bytes --]

Don't fetch CS explicitly, leverage the fact that hvm_emulate_prepare()
already does (and that hvm_virtual_to_linear_addr() doesn't alter it).

At once increase the length passed to hvm_virtual_to_linear_addr() by
one: There definitely needs to be at least one more opcode byte, and we
can avoid missing a wraparound case this way.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3834,19 +3834,20 @@ void hvm_ud_intercept(struct cpu_user_re
 {
     struct hvm_emulate_ctxt ctxt;
 
+    hvm_emulate_prepare(&ctxt, regs);
+
     if ( opt_hvm_fep )
     {
         struct vcpu *cur = current;
-        struct segment_register cs;
+        const struct segment_register *cs = &ctxt.seg_reg[x86_seg_cs];
         unsigned long addr;
         char sig[5]; /* ud2; .ascii "xen" */
 
-        hvm_get_segment_register(cur, x86_seg_cs, &cs);
-        if ( hvm_virtual_to_linear_addr(x86_seg_cs, &cs, regs->eip,
-                                        sizeof(sig), hvm_access_insn_fetch,
+        if ( hvm_virtual_to_linear_addr(x86_seg_cs, cs, regs->eip,
+                                        sizeof(sig) + 1, hvm_access_insn_fetch,
                                         (hvm_long_mode_enabled(cur) &&
-                                         cs.attr.fields.l) ? 64 :
-                                        cs.attr.fields.db ? 32 : 16, &addr) &&
+                                         cs->attr.fields.l) ? 64 :
+                                        cs->attr.fields.db ? 32 : 16, &addr) &&
              (hvm_fetch_from_guest_virt_nofault(sig, addr, sizeof(sig),
                                                 0) == HVMCOPY_okay) &&
              (memcmp(sig, "\xf\xbxen", sizeof(sig)) == 0) )
@@ -3856,8 +3857,6 @@ void hvm_ud_intercept(struct cpu_user_re
         }
     }
 
-    hvm_emulate_prepare(&ctxt, regs);
-
     switch ( hvm_emulate_one(&ctxt) )
     {
     case X86EMUL_UNHANDLEABLE:




[-- Attachment #2: x86-HVM-fep-reorder.patch --]
[-- Type: text/plain, Size: 2068 bytes --]

x86/HVM: re-order operations in hvm_ud_intercept()

Don't fetch CS explicitly, leverage the fact that hvm_emulate_prepare()
already does (and that hvm_virtual_to_linear_addr() doesn't alter it).

At once increase the length passed to hvm_virtual_to_linear_addr() by
one: There definitely needs to be at least one more opcode byte, and we
can avoid missing a wraparound case this way.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3834,19 +3834,20 @@ void hvm_ud_intercept(struct cpu_user_re
 {
     struct hvm_emulate_ctxt ctxt;
 
+    hvm_emulate_prepare(&ctxt, regs);
+
     if ( opt_hvm_fep )
     {
         struct vcpu *cur = current;
-        struct segment_register cs;
+        const struct segment_register *cs = &ctxt.seg_reg[x86_seg_cs];
         unsigned long addr;
         char sig[5]; /* ud2; .ascii "xen" */
 
-        hvm_get_segment_register(cur, x86_seg_cs, &cs);
-        if ( hvm_virtual_to_linear_addr(x86_seg_cs, &cs, regs->eip,
-                                        sizeof(sig), hvm_access_insn_fetch,
+        if ( hvm_virtual_to_linear_addr(x86_seg_cs, cs, regs->eip,
+                                        sizeof(sig) + 1, hvm_access_insn_fetch,
                                         (hvm_long_mode_enabled(cur) &&
-                                         cs.attr.fields.l) ? 64 :
-                                        cs.attr.fields.db ? 32 : 16, &addr) &&
+                                         cs->attr.fields.l) ? 64 :
+                                        cs->attr.fields.db ? 32 : 16, &addr) &&
              (hvm_fetch_from_guest_virt_nofault(sig, addr, sizeof(sig),
                                                 0) == HVMCOPY_okay) &&
              (memcmp(sig, "\xf\xbxen", sizeof(sig)) == 0) )
@@ -3856,8 +3857,6 @@ void hvm_ud_intercept(struct cpu_user_re
         }
     }
 
-    hvm_emulate_prepare(&ctxt, regs);
-
     switch ( hvm_emulate_one(&ctxt) )
     {
     case X86EMUL_UNHANDLEABLE:

[-- Attachment #3: Type: text/plain, Size: 126 bytes --]

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  parent reply	other threads:[~2016-06-08 13:43 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-08 13:35 [PATCH] x86/HVM: mis adjustments Jan Beulich
2016-06-08 13:42 ` [PATCH 1/2] x86/HVM: constify hvm_virtual_to_linear_addr()'s segment register parameter Jan Beulich
2016-06-09 11:25   ` Andrew Cooper
2016-06-08 13:43 ` Jan Beulich [this message]
2016-06-09 11:34   ` [PATCH 2/2] x86/HVM: re-order operations in hvm_ud_intercept() Andrew Cooper
2016-06-09 12:31     ` Jan Beulich
2016-06-09 14:06       ` Andrew Cooper
2016-06-09 14:13         ` Jan Beulich
2016-06-09 14:27           ` Andrew Cooper
2016-06-09 15:05             ` Jan Beulich
2016-06-17  8:19               ` Ping: " Jan Beulich
2016-06-17  9:37               ` Andrew Cooper
2016-06-17 10:01                 ` Jan Beulich

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