File 5b72fbbf-3-shadow-Infrastructure-to-force-a-PV-... of Package xen

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File 5b72fbbf-3-shadow-Infrastructure-to-force-a-PV-guest-into-shadow-mode.patch of Package xen (Revision 53c4fee2aedc229202ee13c62f9d7331)

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Subject: x86/shadow: Infrastructure to force a PV guest into shadow mode
From: Juergen Gross jgross@suse.com Mon Jul 23 07:11:40 2018 +0100
Date: Tue Aug 14 17:15:14 2018 +0100:
Git: 02d2c660935cfd6ff2438afb3892776dfc7db711

To mitigate L1TF, we cannot alter an architecturally-legitimate PTE a PV guest
chooses to write, but we can force the PV domain into shadow mode so Xen
controls the PTEs which are reachable by the CPU pagewalk.

Introduce new shadow mode, PG_SH_forced, and a tasklet to perform the
transition.  Later patches will introduce the logic to enable this mode at the
appropriate time.

To simplify vcpu cleanup, make tasklet_kill() idempotent with respect to
tasklet_init(), which involves adding a helper to check for an uninitialised
list head.

This is part of XSA-273 / CVE-2018-3620.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit b76ec3946bf6caca2c3950b857c008bc8db6723f)

diff --git a/xen/arch/x86/mm/paging.c b/xen/arch/x86/mm/paging.c
index 2b0445ffe9..dcee496eb0 100644
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -873,6 +873,8 @@ void paging_dump_domain_info(struct domain *d)
         printk("    paging assistance: ");
         if ( paging_mode_shadow(d) )
             printk("shadow ");
+        if ( paging_mode_sh_forced(d) )
+            printk("forced ");
         if ( paging_mode_hap(d) )
             printk("hap ");
         if ( paging_mode_refcounts(d) )
diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index dd61b50eb7..fd42d734e7 100644
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -3177,6 +3177,15 @@ static void sh_new_mode(struct domain *d, u32 new_mode)
     ASSERT(paging_locked_by_me(d));
     ASSERT(d != current->domain);
 
+    /*
+     * If PG_SH_forced has previously been activated because of writing an
+     * L1TF-vulnerable PTE, it must remain active for the remaining lifetime
+     * of the domain, even if the logdirty mode needs to be controlled for
+     * migration purposes.
+     */
+    if ( paging_mode_sh_forced(d) )
+        new_mode |= PG_SH_forced | PG_SH_enable;
+
     d->arch.paging.mode = new_mode;
     for_each_vcpu(d, v)
         sh_update_paging_modes(v);
@@ -4057,6 +4066,33 @@ void shadow_audit_tables(struct vcpu *v)
 
 #endif /* Shadow audit */
 
+#ifdef CONFIG_PV
+
+void pv_l1tf_tasklet(unsigned long data)
+{
+    struct domain *d = (void *)data;
+
+    domain_pause(d);
+    paging_lock(d);
+
+    if ( !paging_mode_sh_forced(d) && !d->is_dying )
+    {
+        int ret = shadow_one_bit_enable(d, PG_SH_forced);
+
+        if ( ret )
+        {
+            printk(XENLOG_G_ERR "d%d Failed to enable PG_SH_forced: %d\n",
+                   d->domain_id, ret);
+            domain_crash(d);
+        }
+    }
+
+    paging_unlock(d);
+    domain_unpause(d);
+}
+
+#endif /* CONFIG_PV */
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/x86/pv/domain.c b/xen/arch/x86/pv/domain.c
index a4f0bd239d..3230ac6a22 100644
--- a/xen/arch/x86/pv/domain.c
+++ b/xen/arch/x86/pv/domain.c
@@ -13,6 +13,7 @@
 #include <asm/invpcid.h>
 #include <asm/spec_ctrl.h>
 #include <asm/pv/domain.h>
+#include <asm/shadow.h>
 
 static __read_mostly enum {
     PCID_OFF,
@@ -209,6 +210,8 @@ int pv_vcpu_initialise(struct vcpu *v)
 
 void pv_domain_destroy(struct domain *d)
 {
+    pv_l1tf_domain_destroy(d);
+
     destroy_perdomain_mapping(d, GDT_LDT_VIRT_START,
                               GDT_LDT_MBYTES << (20 - PAGE_SHIFT));
 
@@ -229,6 +232,8 @@ int pv_domain_initialise(struct domain *d)
     };
     int rc = -ENOMEM;
 
+    pv_l1tf_domain_init(d);
+
     d->arch.pv_domain.gdt_ldt_l1tab =
         alloc_xenheap_pages(0, MEMF_node(domain_to_node(d)));
     if ( !d->arch.pv_domain.gdt_ldt_l1tab )
diff --git a/xen/common/tasklet.c b/xen/common/tasklet.c
index 0f0a6f8365..d4fea3151c 100644
--- a/xen/common/tasklet.c
+++ b/xen/common/tasklet.c
@@ -156,6 +156,10 @@ void tasklet_kill(struct tasklet *t)
 
     spin_lock_irqsave(&tasklet_lock, flags);
 
+    /* Cope with uninitialised tasklets. */
+    if ( list_head_is_null(&t->list) )
+        goto unlock;
+
     if ( !list_empty(&t->list) )
     {
         BUG_ON(t->is_dead || t->is_running || (t->scheduled_on < 0));
@@ -172,6 +176,7 @@ void tasklet_kill(struct tasklet *t)
         spin_lock_irqsave(&tasklet_lock, flags);
     }
 
+ unlock:
     spin_unlock_irqrestore(&tasklet_lock, flags);
 }
 
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index e0d413c7de..61e6900465 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -121,6 +121,11 @@ struct shadow_domain {
 
     /* Has this domain ever used HVMOP_pagetable_dying? */
     bool_t pagetable_dying_op;
+
+#ifdef CONFIG_PV
+    /* PV L1 Terminal Fault mitigation. */
+    struct tasklet pv_l1tf_tasklet;
+#endif /* CONFIG_PV */
 #endif
 };
 
@@ -257,6 +262,8 @@ struct pv_domain
     bool xpti;
     /* Use PCID feature? */
     bool pcid;
+    /* Mitigate L1TF with shadow/crashing? */
+    bool check_l1tf;
 
     /* map_domain_page() mapping cache. */
     struct mapcache_domain mapcache;
diff --git a/xen/include/asm-x86/paging.h b/xen/include/asm-x86/paging.h
index f0085511c7..f440e3e53c 100644
--- a/xen/include/asm-x86/paging.h
+++ b/xen/include/asm-x86/paging.h
@@ -37,11 +37,14 @@
 
 #define PG_SH_shift    20
 #define PG_HAP_shift   21
+#define PG_SHF_shift   22
 /* We're in one of the shadow modes */
 #ifdef CONFIG_SHADOW_PAGING
 #define PG_SH_enable   (1U << PG_SH_shift)
+#define PG_SH_forced   (1U << PG_SHF_shift)
 #else
 #define PG_SH_enable   0
+#define PG_SH_forced   0
 #endif
 #define PG_HAP_enable  (1U << PG_HAP_shift)
 
@@ -62,6 +65,7 @@
 
 #define paging_mode_enabled(_d)   (!!(_d)->arch.paging.mode)
 #define paging_mode_shadow(_d)    (!!((_d)->arch.paging.mode & PG_SH_enable))
+#define paging_mode_sh_forced(_d) (!!((_d)->arch.paging.mode & PG_SH_forced))
 #define paging_mode_hap(_d)       (!!((_d)->arch.paging.mode & PG_HAP_enable))
 
 #define paging_mode_refcounts(_d) (!!((_d)->arch.paging.mode & PG_refcounts))
diff --git a/xen/include/asm-x86/shadow.h b/xen/include/asm-x86/shadow.h
index 94a34fd16a..14afb7db52 100644
--- a/xen/include/asm-x86/shadow.h
+++ b/xen/include/asm-x86/shadow.h
@@ -29,6 +29,7 @@
 #include <asm/flushtlb.h>
 #include <asm/paging.h>
 #include <asm/p2m.h>
+#include <asm/spec_ctrl.h>
 
 /*****************************************************************************
  * Macros to tell which shadow paging mode a domain is in*/
@@ -115,6 +116,37 @@ static inline int shadow_domctl(struct domain *d,
 
 #endif /* CONFIG_SHADOW_PAGING */
 
+/*
+ * Mitigations for L1TF / CVE-2018-3620 for PV guests.
+ *
+ * We cannot alter an architecturally-legitimate PTE which a PV guest has
+ * chosen to write, as traditional paged-out metadata is L1TF-vulnerable.
+ * What we can do is force a PV guest which writes a vulnerable PTE into
+ * shadow mode, so Xen controls the pagetables which are reachable by the CPU
+ * pagewalk.
+ */
+
+void pv_l1tf_tasklet(unsigned long data);
+
+static inline void pv_l1tf_domain_init(struct domain *d)
+{
+    d->arch.pv_domain.check_l1tf =
+        opt_pv_l1tf & (is_hardware_domain(d)
+                       ? OPT_PV_L1TF_DOM0 : OPT_PV_L1TF_DOMU);
+
+#if defined(CONFIG_SHADOW_PAGING) && defined(CONFIG_PV)
+    tasklet_init(&d->arch.paging.shadow.pv_l1tf_tasklet,
+                 pv_l1tf_tasklet, (unsigned long)d);
+#endif
+}
+
+static inline void pv_l1tf_domain_destroy(struct domain *d)
+{
+#if defined(CONFIG_SHADOW_PAGING) && defined(CONFIG_PV)
+    tasklet_kill(&d->arch.paging.shadow.pv_l1tf_tasklet);
+#endif
+}
+
 /* Remove all shadows of the guest mfn. */
 static inline void shadow_remove_all_shadows(struct domain *d, mfn_t gmfn)
 {
diff --git a/xen/include/xen/list.h b/xen/include/xen/list.h
index fa07d720ee..1387abb211 100644
--- a/xen/include/xen/list.h
+++ b/xen/include/xen/list.h
@@ -51,6 +51,11 @@ static inline void INIT_LIST_HEAD(struct list_head *list)
     list->prev = list;
 }
 
+static inline bool list_head_is_null(const struct list_head *list)
+{
+    return !list->next && !list->prev;
+}
+
 /*
  * Insert a new entry between two known consecutive entries. 
  *

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File 5b72fbbf-3-shadow-Infrastructure-to-force-a-PV-guest-into-shadow-mode.patch of Package xen (Revision 53c4fee2aedc229202ee13c62f9d7331)

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