[Xen-changelog] [xen stable-4.9] x86/cpu: Fix IST handling during PCPU bringup

[patchbot@xxxxxxx]

commit de38e28cc2cc62e6e9e4741403e4a8f6c07d8cfd
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Oct 12 15:08:34 2017 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Oct 12 15:08:34 2017 +0200

    x86/cpu: Fix IST handling during PCPU bringup
    
    Clear IST references in newly allocated IDTs.  Nothing good will come of
    having them set before the TSS is suitably constructed (although the chances
    of the CPU surviving such an IST interrupt/exception is extremely slim).
    
    Uniformly set the IST references after the TSS is in place.  This fixes an
    issue on AMD hardware, where onlining a PCPU while PCPU0 is in HVM context
    will cause IST_NONE to be copied into the new IDT, making that PCPU 
vulnerable
    to privilege escalation from PV guests until it subsequently schedules an 
HVM
    guest.
    
    This is XSA-244.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: cc08c73c8c1f5ba5ed0f8274548db6725e1c3157
    master date: 2017-10-12 14:50:31 +0200
---
 xen/arch/x86/cpu/common.c | 5 +++++
 xen/arch/x86/smpboot.c    | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 78f5667..6cf3628 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -640,6 +640,7 @@ void __init early_cpu_init(void)
  * - Sets up TSS with stack pointers, including ISTs
  * - Inserts TSS selector into regular and compat GDTs
  * - Loads GDT, IDT, TR then null LDT
+ * - Sets up IST references in the IDT
  */
 void load_system_tables(void)
 {
@@ -702,6 +703,10 @@ void load_system_tables(void)
        asm volatile ("ltr  %w0" : : "rm" (TSS_ENTRY << 3) );
        asm volatile ("lldt %w0" : : "rm" (0) );
 
+       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);
+
        /*
         * Bottom-of-stack must be 16-byte aligned!
         *
diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 50b907b..26b5301 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -724,6 +724,9 @@ static int cpu_smpboot_alloc(unsigned int cpu)
     if ( idt_tables[cpu] == NULL )
         goto oom;
     memcpy(idt_tables[cpu], idt_table, IDT_ENTRIES * sizeof(idt_entry_t));
+    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);
 
     for ( stub_page = 0, i = cpu & ~(STUBS_PER_PAGE - 1);
           i < nr_cpu_ids && i <= (cpu | (STUBS_PER_PAGE - 1)); ++i )
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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