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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 v3] x86/HVM: don't #GP/#SS on wrapping virt->linear translations
Date: Mon, 10 Jul 2017 04:39:05 -0600	[thread overview]
Message-ID: <59637569020000780016A34F@prv-mh.provo.novell.com> (raw)
In-Reply-To: 59637569020000780016A34F@prv-mh.provo.novell.com

[-- Attachment #1: Type: text/plain, Size: 2519 bytes --]

Real hardware wraps silently in most cases, so we should behave the
same. Also split real and VM86 mode handling, as the latter really
ought to have limit checks applied.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v3: Restore 32-bit wrap check for AMD.
v2: Extend to non-64-bit modes. Reduce 64-bit check to a single
    is_canonical_address() invocation.

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2416,16 +2416,21 @@ bool_t hvm_virtual_to_linear_addr(
      */
     ASSERT(seg < x86_seg_none);
 
-    if ( !(curr->arch.hvm_vcpu.guest_cr[0] & X86_CR0_PE) ||
-         (guest_cpu_user_regs()->eflags & X86_EFLAGS_VM) )
+    if ( !(curr->arch.hvm_vcpu.guest_cr[0] & X86_CR0_PE) )
     {
         /*
-         * REAL/VM86 MODE: Don't bother with segment access checks.
+         * REAL MODE: Don't bother with segment access checks.
          * Certain of them are not done in native real mode anyway.
          */
         addr = (uint32_t)(addr + reg->base);
-        last_byte = (uint32_t)addr + bytes - !!bytes;
-        if ( last_byte < addr )
+    }
+    else if ( (guest_cpu_user_regs()->eflags & X86_EFLAGS_VM) &&
+              is_x86_user_segment(seg) )
+    {
+        /* VM86 MODE: Fixed 64k limits on all user segments. */
+        addr = (uint32_t)(addr + reg->base);
+        last_byte = (uint32_t)offset + bytes - !!bytes;
+        if ( max(offset, last_byte) >> 16 )
             goto out;
     }
     else if ( hvm_long_mode_active(curr) &&
@@ -2447,8 +2452,7 @@ bool_t hvm_virtual_to_linear_addr(
             addr += reg->base;
 
         last_byte = addr + bytes - !!bytes;
-        if ( !is_canonical_address(addr) || last_byte < addr ||
-             !is_canonical_address(last_byte) )
+        if ( !is_canonical_address((long)addr < 0 ? addr : last_byte) )
             goto out;
     }
     else
@@ -2498,8 +2502,11 @@ bool_t hvm_virtual_to_linear_addr(
             if ( (offset <= reg->limit) || (last_byte < offset) )
                 goto out;
         }
-        else if ( (last_byte > reg->limit) || (last_byte < offset) )
-            goto out; /* last byte is beyond limit or wraps 0xFFFFFFFF */
+        else if ( last_byte > reg->limit )
+            goto out; /* last byte is beyond limit */
+        else if ( last_byte < offset &&
+                  curr->domain->arch.cpuid->x86_vendor == X86_VENDOR_AMD )
+            goto out; /* access wraps */
     }
 
     /* All checks ok. */




[-- Attachment #2: x86-HVM-v2l-wrap.patch --]
[-- Type: text/plain, Size: 2577 bytes --]

x86/HVM: don't #GP/#SS on wrapping virt->linear translations

Real hardware wraps silently in most cases, so we should behave the
same. Also split real and VM86 mode handling, as the latter really
ought to have limit checks applied.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v3: Restore 32-bit wrap check for AMD.
v2: Extend to non-64-bit modes. Reduce 64-bit check to a single
    is_canonical_address() invocation.

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2416,16 +2416,21 @@ bool_t hvm_virtual_to_linear_addr(
      */
     ASSERT(seg < x86_seg_none);
 
-    if ( !(curr->arch.hvm_vcpu.guest_cr[0] & X86_CR0_PE) ||
-         (guest_cpu_user_regs()->eflags & X86_EFLAGS_VM) )
+    if ( !(curr->arch.hvm_vcpu.guest_cr[0] & X86_CR0_PE) )
     {
         /*
-         * REAL/VM86 MODE: Don't bother with segment access checks.
+         * REAL MODE: Don't bother with segment access checks.
          * Certain of them are not done in native real mode anyway.
          */
         addr = (uint32_t)(addr + reg->base);
-        last_byte = (uint32_t)addr + bytes - !!bytes;
-        if ( last_byte < addr )
+    }
+    else if ( (guest_cpu_user_regs()->eflags & X86_EFLAGS_VM) &&
+              is_x86_user_segment(seg) )
+    {
+        /* VM86 MODE: Fixed 64k limits on all user segments. */
+        addr = (uint32_t)(addr + reg->base);
+        last_byte = (uint32_t)offset + bytes - !!bytes;
+        if ( max(offset, last_byte) >> 16 )
             goto out;
     }
     else if ( hvm_long_mode_active(curr) &&
@@ -2447,8 +2452,7 @@ bool_t hvm_virtual_to_linear_addr(
             addr += reg->base;
 
         last_byte = addr + bytes - !!bytes;
-        if ( !is_canonical_address(addr) || last_byte < addr ||
-             !is_canonical_address(last_byte) )
+        if ( !is_canonical_address((long)addr < 0 ? addr : last_byte) )
             goto out;
     }
     else
@@ -2498,8 +2502,11 @@ bool_t hvm_virtual_to_linear_addr(
             if ( (offset <= reg->limit) || (last_byte < offset) )
                 goto out;
         }
-        else if ( (last_byte > reg->limit) || (last_byte < offset) )
-            goto out; /* last byte is beyond limit or wraps 0xFFFFFFFF */
+        else if ( last_byte > reg->limit )
+            goto out; /* last byte is beyond limit */
+        else if ( last_byte < offset &&
+                  curr->domain->arch.cpuid->x86_vendor == X86_VENDOR_AMD )
+            goto out; /* access wraps */
     }
 
     /* All checks ok. */

[-- Attachment #3: Type: text/plain, Size: 127 bytes --]

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       reply	other threads:[~2017-07-10 10:39 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-10 10:39 Jan Beulich [this message]
2017-08-10  7:19 ` Ping: [PATCH v3] x86/HVM: don't #GP/#SS on wrapping virt->linear translations Jan Beulich
2017-08-25 14:59   ` Ping#2: " Jan Beulich
2017-12-04 10:16   ` Ping#3: " Jan Beulich
2017-12-04 16:39     ` Andrew Cooper
2017-12-06  7:44       ` Jan Beulich
2018-02-28 14:51       ` Ping: " Jan Beulich
2017-09-05 12:26 ` Andrew Cooper
2017-09-05 13:30   ` Jan Beulich

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