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commit 9d7687d60ae2e09ad2a77b05bd820e7850709375
Author: Tim Deegan <tim@xen.org>
Date:   Wed Mar 16 16:56:04 2016 +0000

    x86: limit GFNs to 32 bits for shadowed superpages.
    
    Superpage shadows store the shadowed GFN in the backpointer field,
    which for non-BIGMEM builds is 32 bits wide.  Shadowing a superpage
    mapping of a guest-physical address above 2^44 would lead to the GFN
    being truncated there, and a crash when we come to remove the shadow
    from the hash table.
    
    Track the valid width of a GFN for each guest, including reporting it
    through CPUID, and enforce it in the shadow pagetables.  Set the
    maximum witth to 32 for guests where this truncation could occur.
    
    This is XSA-173.
    
    Signed-off-by: Tim Deegan <tim@xen.org>
    Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reported-by: Ling Liu <liuling-it@360.cn>
diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 5c8d3c2..7dc8220 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -37,6 +37,7 @@ integer_param("cpuid_mask_ext_edx", opt_cpuid_mask_ext_edx);
 struct cpu_dev * cpu_devs[X86_VENDOR_NUM] = {};
 
 unsigned int paddr_bits __read_mostly = 36;
+unsigned int hap_paddr_bits __read_mostly = 36;
 
 /*
  * Default host IA32_CR_PAT value to cover all memory types.
@@ -209,7 +210,7 @@ static void __init early_cpu_detect(void)
 
 static void __cpuinit generic_identify(struct cpuinfo_x86 *c)
 {
-	u32 tfms, capability, excap, ebx;
+	u32 tfms, capability, excap, ebx, eax;
 
 	/* Get vendor name */
 	cpuid(0x00000000, &c->cpuid_level,
@@ -246,8 +247,11 @@ static void __cpuinit generic_identify(struct cpuinfo_x86 *c)
 		}
 		if ( c->extended_cpuid_level >= 0x80000004 )
 			get_model_name(c); /* Default name */
-		if ( c->extended_cpuid_level >= 0x80000008 )
-			paddr_bits = cpuid_eax(0x80000008) & 0xff;
+		if ( c->extended_cpuid_level >= 0x80000008 ) {
+			eax = cpuid_eax(0x80000008);
+			paddr_bits = eax & 0xff;
+			hap_paddr_bits = ((eax >> 16) & 0xff) ?: paddr_bits;
+		}
 	}
 
 	/* Might lift BIOS max_leaf=3 limit. */
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 41fb10a..cac458a 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4327,8 +4327,7 @@ void hvm_cpuid(unsigned int input, unsigned int *eax, unsigned int *ebx,
         break;
 
     case 0x80000008:
-        count = cpuid_eax(0x80000008);
-        count = (count >> 16) & 0xff ?: count & 0xff;
+        count = d->arch.paging.gfn_bits + PAGE_SHIFT;
         if ( (*eax & 0xff) > count )
             *eax = (*eax & ~0xff) | count;
 
diff --git a/xen/arch/x86/mm/guest_walk.c b/xen/arch/x86/mm/guest_walk.c
index 1b26175..50ba7d5 100644
--- a/xen/arch/x86/mm/guest_walk.c
+++ b/xen/arch/x86/mm/guest_walk.c
@@ -94,6 +94,12 @@ void *map_domain_gfn(struct p2m_domain *p2m, gfn_t gfn, mfn_t *mfn,
     struct page_info *page;
     void *map;
 
+    if ( gfn_x(gfn) >> p2m->domain->arch.paging.gfn_bits )
+    {
+        *rc = _PAGE_INVALID_BIT;
+        return NULL;
+    }
+
     /* Translate the gfn, unsharing if shared */
     page = get_page_from_gfn_p2m(p2m->domain, p2m, gfn_x(gfn), p2mt, NULL,
                                  q);
@@ -327,20 +333,8 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
             flags &= ~_PAGE_PAT;
 
         if ( gfn_x(start) & GUEST_L2_GFN_MASK & ~0x1 )
-        {
-#if GUEST_PAGING_LEVELS == 2
-            /*
-             * Note that _PAGE_INVALID_BITS is zero in this case, yielding a
-             * no-op here.
-             *
-             * Architecturally, the walk should fail if bit 21 is set (others
-             * aren't being checked at least in PSE36 mode), but we'll ignore
-             * this here in order to avoid specifying a non-natural, non-zero
-             * _PAGE_INVALID_BITS value just for that case.
-             */
-#endif
             rc |= _PAGE_INVALID_BITS;
-        }
+
         /* Increment the pfn by the right number of 4k pages.  
          * Mask out PAT and invalid bits. */
         start = _gfn((gfn_x(start) & ~GUEST_L2_GFN_MASK) +
@@ -423,5 +417,11 @@ set_ad:
         put_page(mfn_to_page(mfn_x(gw->l1mfn)));
     }
 
+    /* If this guest has a restricted physical address space then the
+     * target GFN must fit within it. */
+    if ( !(rc & _PAGE_PRESENT)
+         && gfn_x(guest_l1e_get_gfn(gw->l1e)) >> d->arch.paging.gfn_bits )
+        rc |= _PAGE_INVALID_BITS;
+
     return rc;
 }
diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 0c80012..84531b1 100644
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -429,6 +429,8 @@ void hap_domain_init(struct domain *d)
 {
     INIT_PAGE_LIST_HEAD(&d->arch.paging.hap.freelist);
 
+    d->arch.paging.gfn_bits = hap_paddr_bits - PAGE_SHIFT;
+
     /* Use HAP logdirty mechanism. */
     paging_log_dirty_init(d, hap_enable_log_dirty,
                           hap_disable_log_dirty,
diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index 18026fe..9028d82 100644
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -48,6 +48,16 @@ void shadow_domain_init(struct domain *d, unsigned int domcr_flags)
     INIT_PAGE_LIST_HEAD(&d->arch.paging.shadow.freelist);
     INIT_PAGE_LIST_HEAD(&d->arch.paging.shadow.pinned_shadows);
 
+    d->arch.paging.gfn_bits = paddr_bits - PAGE_SHIFT;
+#ifndef CONFIG_BIGMEM
+    /*
+     * Shadowed superpages store GFNs in 32-bit page_info fields.
+     * Note that we cannot use guest_supports_superpages() here.
+     */
+    if ( !is_pv_domain(d) || opt_allow_superpage )
+        d->arch.paging.gfn_bits = 32;
+#endif
+
     /* Use shadow pagetables for log-dirty support */
     paging_log_dirty_init(d, shadow_enable_log_dirty, 
                           shadow_disable_log_dirty, shadow_clean_dirty_bitmap);
diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index d6802ff..7589d23 100644
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -527,7 +527,8 @@ _sh_propagate(struct vcpu *v,
     ASSERT(GUEST_PAGING_LEVELS > 3 || level != 3);
 
     /* Check there's something for the shadows to map to */
-    if ( !p2m_is_valid(p2mt) && !p2m_is_grant(p2mt) )
+    if ( (!p2m_is_valid(p2mt) && !p2m_is_grant(p2mt))
+         || gfn_x(target_gfn) >> d->arch.paging.gfn_bits )
     {
         *sp = shadow_l1e_empty();
         goto done;
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index 6a77a93..e8df4a9 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -188,6 +188,9 @@ struct paging_domain {
     /* log dirty support */
     struct log_dirty_domain log_dirty;
 
+    /* Number of valid bits in a gfn. */
+    unsigned int gfn_bits;
+
     /* preemption handling */
     struct {
         const struct domain *dom;
diff --git a/xen/include/asm-x86/guest_pt.h b/xen/include/asm-x86/guest_pt.h
index d2a8250..d95f835 100644
--- a/xen/include/asm-x86/guest_pt.h
+++ b/xen/include/asm-x86/guest_pt.h
@@ -220,15 +220,17 @@ guest_supports_nx(struct vcpu *v)
 }
 
 
-/* Some bits are invalid in any pagetable entry. */
-#if GUEST_PAGING_LEVELS == 2
-#define _PAGE_INVALID_BITS (0)
-#elif GUEST_PAGING_LEVELS == 3
-#define _PAGE_INVALID_BITS \
-    get_pte_flags(((1ull<<63) - 1) & ~((1ull<<paddr_bits) - 1))
-#else /* GUEST_PAGING_LEVELS == 4 */
+/*
+ * Some bits are invalid in any pagetable entry.
+ * Normal flags values get represented in 24-bit values (see
+ * get_pte_flags() and put_pte_flags()), so set bit 24 in
+ * addition to be able to flag out of range frame numbers.
+ */
+#if GUEST_PAGING_LEVELS == 3
 #define _PAGE_INVALID_BITS \
-    get_pte_flags(((1ull<<52) - 1) & ~((1ull<<paddr_bits) - 1))
+    (_PAGE_INVALID_BIT | get_pte_flags(((1ull << 63) - 1) & ~(PAGE_SIZE - 1)))
+#else /* 2-level and 4-level */
+#define _PAGE_INVALID_BITS _PAGE_INVALID_BIT
 #endif
 
 
diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
index b4e4731..56fc5a2 100644
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -203,6 +203,8 @@ extern u32 cpuid_ext_features;
 
 /* Maximum width of physical addresses supported by the hardware */
 extern unsigned int paddr_bits;
+/* Max physical address width supported within HAP guests */
+extern unsigned int hap_paddr_bits;
 
 extern void identify_cpu(struct cpuinfo_x86 *);
 extern void setup_clear_cpu_cap(unsigned int);
diff --git a/xen/include/asm-x86/x86_64/page.h b/xen/include/asm-x86/x86_64/page.h
index 1d54587..f1d1b6c 100644
--- a/xen/include/asm-x86/x86_64/page.h
+++ b/xen/include/asm-x86/x86_64/page.h
@@ -141,6 +141,12 @@ typedef l4_pgentry_t root_pgentry_t;
 #define _PAGE_GNTTAB (1U<<22)
 
 /*
+ * Bit 24 of a 24-bit flag mask!  This is not any bit of a real pte,
+ * and is only used for signalling in variables that contain flags.
+ */
+#define _PAGE_INVALID_BIT (1U<<24)
+
+/*
  * Bit 12 of a 24-bit flag mask. This corresponds to bit 52 of a pte.
  * This is needed to distinguish between user and kernel PTEs since _PAGE_USER
  * is asserted for both.