x86: don't crash when mapping a page using EFI runtime page tables

When an interrupt is received during an EFI runtime service call, Xen
may call map_domain_page() while using the EFI runtime page tables.
This fails because, although the EFI runtime page tables are a
copy of the idle domain's page tables, current points at a different
domain's vCPU.

To fix this, return NULL from mapcache_current_vcpu() when using the EFI
runtime page tables which is treated equivalently to running in an idle
vCPU.

This issue can be reproduced by repeatedly calling GetVariable() from
dom0 while using VT-d, since VT-d frequently maps a page from interrupt
context.

Example call trace:
[<ffff82d0801615dc>] __find_next_zero_bit+0x28/0x60
[<ffff82d08016a10e>] map_domain_page+0x4c6/0x4eb
[<ffff82d080156ae6>] map_vtd_domain_page+0xd/0xf
[<ffff82d08015533a>] msi_msg_read_remap_rte+0xe3/0x1d8
[<ffff82d08014e516>] iommu_read_msi_from_ire+0x31/0x34
[<ffff82d08016ff6c>] set_msi_affinity+0x134/0x17a
[<ffff82d0801737b5>] move_masked_irq+0x5c/0x98
[<ffff82d080173816>] move_native_irq+0x25/0x36
[<ffff82d08016ffcb>] ack_nonmaskable_msi_irq+0x19/0x20
[<ffff82d08016ffdb>] ack_maskable_msi_irq+0x9/0x37
[<ffff82d080173e8b>] do_IRQ+0x251/0x635
[<ffff82d080234502>] common_interrupt+0x62/0x70
[<00000000df7ed2be>] 00000000df7ed2be

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
master commit: 591e1e357c29589e9d6121d8faadc4f4d3b9013e
master date: 2015-06-01 11:59:14 +0200

diff --git a/xen/arch/x86/domain_page.c b/xen/arch/x86/domain_page.c
index 158a1645d74fa9c38e6417b2c40f616db4d4017f..9bdab61354129c5401d00d41ff228a1e2d4cda4d 100644 (file)
--- a/xen/arch/x86/domain_page.c
+++ b/xen/arch/x86/domain_page.c
@@ -31,6 +31,14 @@ static inline struct vcpu *mapcache_current_vcpu(void)
     if ( v == (struct vcpu *)0xfffff000 )
         return NULL;
 
+    /*
+     * When using efi runtime page tables, we have the equivalent of the idle
+     * domain's page tables but current may point at another domain's VCPU.
+     * Return NULL as though current is not properly set up yet.
+     */
+    if ( efi_enabled && efi_rs_using_pgtables() )
+        return NULL;
+
     /*
      * If guest_table is NULL, and we are running a paravirtualised guest,
      * then it means we are running on the idle domain's page table and must
@@ -38,14 +46,11 @@ static inline struct vcpu *mapcache_current_vcpu(void)
      */
     if ( unlikely(pagetable_is_null(v->arch.guest_table)) && is_pv_vcpu(v) )
     {
-        unsigned long cr3;
-
         /* If we really are idling, perform lazy context switch now. */
         if ( (v = idle_vcpu[smp_processor_id()]) == current )
             sync_local_execstate();
         /* We must now be running on the idle page table. */
-        ASSERT((cr3 = read_cr3()) == __pa(idle_pg_table) ||
-               (efi_enabled && cr3 == efi_rs_page_table()));
+        ASSERT(read_cr3() == __pa(idle_pg_table));
     }
 
     return v;

diff --git a/xen/arch/x86/efi/runtime.c b/xen/arch/x86/efi/runtime.c
index 441ec908e4c0b5fbfc3332594dcb5f1e5eb4ba22..fe851d95e413ac947c89cae4612ad8352864b3ac 100644 (file)
--- a/xen/arch/x86/efi/runtime.c
+++ b/xen/arch/x86/efi/runtime.c
@@ -26,6 +26,7 @@ const CHAR16 *__read_mostly efi_fw_vendor;
 
 EFI_RUNTIME_SERVICES *__read_mostly efi_rs;
 static DEFINE_SPINLOCK(efi_rs_lock);
+static unsigned int efi_rs_on_cpu = NR_CPUS;
 
 UINTN __read_mostly efi_memmap_size;
 UINTN __read_mostly efi_mdesc_size;
@@ -67,6 +68,8 @@ unsigned long efi_rs_enter(void)
 
     spin_lock(&efi_rs_lock);
 
+    efi_rs_on_cpu = smp_processor_id();
+
     /* prevent fixup_page_fault() from doing anything */
     irq_enter();
 
@@ -101,13 +104,16 @@ void efi_rs_leave(unsigned long cr3)
         asm volatile ( "lgdt %0" : : "m" (gdt_desc) );
     }
     irq_exit();
+    efi_rs_on_cpu = NR_CPUS;
     spin_unlock(&efi_rs_lock);
     stts();
 }
 
-paddr_t efi_rs_page_table(void)
+bool_t efi_rs_using_pgtables(void)
 {
-    return efi_l4_pgtable ? virt_to_maddr(efi_l4_pgtable) : 0;
+    return efi_l4_pgtable &&
+           (smp_processor_id() == efi_rs_on_cpu) &&
+           (read_cr3() == virt_to_maddr(efi_l4_pgtable));
 }
 
 unsigned long efi_get_time(void)

diff --git a/xen/arch/x86/efi/stub.c b/xen/arch/x86/efi/stub.c
index 627009f43069dc7924329062d9289a5e02281223..07c2bd0c6e6fe516a0227a346fced8a7e84e6756 100644 (file)
--- a/xen/arch/x86/efi/stub.c
+++ b/xen/arch/x86/efi/stub.c
@@ -12,7 +12,7 @@ void __init efi_init_memory(void) { }
 
 void efi_update_l4_pgtable(unsigned int l4idx, l4_pgentry_t l4e) { }
 
-paddr_t efi_rs_page_table(void)
+bool_t efi_rs_using_pgtables(void)
 {
     BUG();
     return 0;

diff --git a/xen/include/xen/efi.h b/xen/include/xen/efi.h
index 5e02724572b798b7691ab14c6d04e4ee4faec48b..f2782ce3e442dd698f111f4eae0d94527b5cec77 100644 (file)
--- a/xen/include/xen/efi.h
+++ b/xen/include/xen/efi.h
@@ -28,7 +28,7 @@ struct xenpf_efi_runtime_call;
 struct compat_pf_efi_runtime_call;
 
 void efi_init_memory(void);
-paddr_t efi_rs_page_table(void);
+bool_t efi_rs_using_pgtables(void);
 unsigned long efi_get_time(void);
 void efi_halt_system(void);
 void efi_reset_system(bool_t warm);