File xsa260-3.patch of Package xen.11298

From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: x86/traps: Use an Interrupt Stack Table for #DB

PV guests can use architectural corner cases to cause #DB to be raised after
transitioning into supervisor mode.

Use an interrupt stack table for #DB to prevent the exception being taken with
a guest controlled stack pointer.

This is part of XSA-260 / CVE-2018-8897.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -612,6 +612,7 @@ void __cpuinit load_system_tables(void)
 	tss->ist[IST_MCE - 1] = stack_top + IST_MCE * PAGE_SIZE;
 	tss->ist[IST_DF  - 1] = stack_top + IST_DF  * PAGE_SIZE;
 	tss->ist[IST_NMI - 1] = stack_top + IST_NMI * PAGE_SIZE;
+	tss->ist[IST_DB  - 1] = stack_top + IST_DB  * PAGE_SIZE;
 
 	_set_tssldt_desc(
 		gdt + TSS_ENTRY,
@@ -632,6 +633,7 @@ void __cpuinit load_system_tables(void)
 	set_ist(&idt_tables[cpu][TRAP_double_fault],  IST_DF);
 	set_ist(&idt_tables[cpu][TRAP_nmi],	      IST_NMI);
 	set_ist(&idt_tables[cpu][TRAP_machine_check], IST_MCE);
+	set_ist(&idt_tables[cpu][TRAP_debug],         IST_DB);
 }
 
 /*
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -999,6 +999,7 @@ static void svm_ctxt_switch_from(struct
     set_ist(&idt_tables[cpu][TRAP_double_fault],  IST_DF);
     set_ist(&idt_tables[cpu][TRAP_nmi],           IST_NMI);
     set_ist(&idt_tables[cpu][TRAP_machine_check], IST_MCE);
+    set_ist(&idt_tables[cpu][TRAP_debug],         IST_DB);
 }
 
 static void svm_ctxt_switch_to(struct vcpu *v)
@@ -1023,6 +1024,7 @@ static void svm_ctxt_switch_to(struct vc
     set_ist(&idt_tables[cpu][TRAP_double_fault],  IST_NONE);
     set_ist(&idt_tables[cpu][TRAP_nmi],           IST_NONE);
     set_ist(&idt_tables[cpu][TRAP_machine_check], IST_NONE);
+    set_ist(&idt_tables[cpu][TRAP_debug],         IST_NONE);
 
     svm_restore_dr(v);
 
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -869,6 +869,7 @@ static int cpu_smpboot_alloc(unsigned in
     set_ist(&idt_tables[cpu][TRAP_double_fault],  IST_NONE);
     set_ist(&idt_tables[cpu][TRAP_nmi],           IST_NONE);
     set_ist(&idt_tables[cpu][TRAP_machine_check], IST_NONE);
+    set_ist(&idt_tables[cpu][TRAP_debug],         IST_NONE);
 
     if ( setup_cpu_root_pgt(cpu) )
         goto oom;
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -3718,6 +3718,7 @@ void __init init_idt_traps(void)
     set_ist(&idt_table[TRAP_double_fault],  IST_DF);
     set_ist(&idt_table[TRAP_nmi],           IST_NMI);
     set_ist(&idt_table[TRAP_machine_check], IST_MCE);
+    set_ist(&idt_table[TRAP_debug],         IST_DB);
 
     /* CPU0 uses the master IDT. */
     idt_tables[0] = idt_table;
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -791,7 +791,7 @@ ENTRY(device_not_available)
 ENTRY(debug)
         pushq $0
         movl  $TRAP_debug,4(%rsp)
-        jmp   handle_exception
+        jmp   handle_ist_exception
 
 ENTRY(int3)
         pushq $0
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -442,7 +442,8 @@ struct __packed __cacheline_aligned tss_
 #define IST_DF   1UL
 #define IST_NMI  2UL
 #define IST_MCE  3UL
-#define IST_MAX  3UL
+#define IST_DB   4UL
+#define IST_MAX  4UL
 
 /* Set the interrupt stack table used by a particular interrupt
  * descriptor table entry. */