[Xen-changelog] [xen stable-4.2] x86: Special case __HYPERVISOR_iret rather more when writing hypercall pages

[patchbot@xxxxxxx]

commit 64afca0c191eb940eefa80c814b5b4d18d648d78
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Sep 12 10:58:40 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Sep 12 10:58:40 2013 +0200

    x86: Special case __HYPERVISOR_iret rather more when writing hypercall pages
    
    In all cases when a hypercall page is written, __HYPERVISOR_iret is first
    written as a regular hypercall, then subsequently rewritten in its special
    case.
    
    For VMX and SVM, this means that following the ud2a instruction is 3 bytes 
of
    an imm32 parameter.  For a ring3 kernel, this means that following the 
syscall
    instruction is the second half of 'pop %r11'.
    
    For a ring1 kernel, the iret case ends up as the same number of bytes as the
    rest of the hypercalls, but it is pointless writing it twice, and is changed
    for consistency.
    
    Therefore, skip the loop iteration which would write the incorrect
    __HYPERVISOR_iret hypercall.  This removes junk machine code from the tail 
and
    makes disassemblers rather more happy when looking at the hypercall page.
    
    Also, a miscellaneous whitespace fix in the comment for ring3 kernel.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: fca11da0ec956b17d7450d7776c3ffa22a8f538a
    master date: 2013-07-16 11:10:45 +0200
---
 xen/arch/x86/hvm/svm/svm.c         |    3 +++
 xen/arch/x86/hvm/vmx/vmx.c         |    3 +++
 xen/arch/x86/x86_64/compat/traps.c |    3 +++
 xen/arch/x86/x86_64/traps.c        |    7 +++++--
 4 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index e74984e..48a3f01 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -763,6 +763,9 @@ static void svm_init_hypercall_page(struct domain *d, void 
*hypercall_page)
 
     for ( i = 0; i < (PAGE_SIZE / 32); i++ )
     {
+        if ( i == __HYPERVISOR_iret )
+            continue;
+
         p = (char *)(hypercall_page + (i * 32));
         *(u8  *)(p + 0) = 0xb8; /* mov imm32, %eax */
         *(u32 *)(p + 1) = i;
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index fa43971..5a3a152 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1008,6 +1008,9 @@ static void vmx_init_hypercall_page(struct domain *d, 
void *hypercall_page)
 
     for ( i = 0; i < (PAGE_SIZE / 32); i++ )
     {
+        if ( i == __HYPERVISOR_iret )
+            continue;
+
         p = (char *)(hypercall_page + (i * 32));
         *(u8  *)(p + 0) = 0xb8; /* mov imm32, %eax */
         *(u32 *)(p + 1) = i;
diff --git a/xen/arch/x86/x86_64/compat/traps.c 
b/xen/arch/x86/x86_64/compat/traps.c
index 03b90b2..6e0ff11 100644
--- a/xen/arch/x86/x86_64/compat/traps.c
+++ b/xen/arch/x86/x86_64/compat/traps.c
@@ -362,6 +362,9 @@ static void hypercall_page_initialise_ring1_kernel(void 
*hypercall_page)
 
     for ( i = 0; i < (PAGE_SIZE / 32); i++ )
     {
+        if ( i == __HYPERVISOR_iret )
+            continue;
+
         p = (char *)(hypercall_page + (i * 32));
         *(u8  *)(p+ 0) = 0xb8;    /* mov  $<i>,%eax */
         *(u32 *)(p+ 1) = i;
diff --git a/xen/arch/x86/x86_64/traps.c b/xen/arch/x86/x86_64/traps.c
index 806cf2e..00bee9b 100644
--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -588,6 +588,9 @@ static void hypercall_page_initialise_ring3_kernel(void 
*hypercall_page)
     /* Fill in all the transfer points with template machine code. */
     for ( i = 0; i < (PAGE_SIZE / 32); i++ )
     {
+        if ( i == __HYPERVISOR_iret )
+            continue;
+
         p = (char *)(hypercall_page + (i * 32));
         *(u8  *)(p+ 0) = 0x51;    /* push %rcx */
         *(u16 *)(p+ 1) = 0x5341;  /* push %r11 */
@@ -600,8 +603,8 @@ static void hypercall_page_initialise_ring3_kernel(void 
*hypercall_page)
     }
 
     /*
-     * HYPERVISOR_iret is special because it doesn't return and expects a 
-     * special stack frame. Guests jump at this transfer point instead of 
+     * HYPERVISOR_iret is special because it doesn't return and expects a
+     * special stack frame. Guests jump at this transfer point instead of
      * calling it.
      */
     p = (char *)(hypercall_page + (__HYPERVISOR_iret * 32));
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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