[Xen-devel] [PATCH v3 2/8] x86/HVM: improve MTRR load checks

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

From: Jan Beulich <jbeulich@xxxxxxxx>

We should not assume that the incoming set of values contains exactly
MTRR_VCNT variable range MSRs. Permit a smaller amount and reject a
bigger one. As a result the save path then also needs to no longer use
a fixed upper bound, in turn requiring unused space in the save record
to be zeroed up front.

Also slightly refine types where appropriate.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
[switch to use MASK_EXTR to get VCNT]
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/hvm/mtrr.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/hvm/mtrr.c b/xen/arch/x86/hvm/mtrr.c
index c298369044..654299a198 100644
--- a/xen/arch/x86/hvm/mtrr.c
+++ b/xen/arch/x86/hvm/mtrr.c
@@ -673,22 +673,22 @@ int hvm_set_mem_pinned_cacheattr(struct domain *d, 
uint64_t gfn_start,
 
 static int hvm_save_mtrr_msr(struct domain *d, hvm_domain_context_t *h)
 {
-    int i;
     struct vcpu *v;
-    struct hvm_hw_mtrr hw_mtrr;
-    struct mtrr_state *mtrr_state;
+
     /* save mtrr&pat */
     for_each_vcpu(d, v)
     {
-        mtrr_state = &v->arch.hvm_vcpu.mtrr;
+        const struct mtrr_state *mtrr_state = &v->arch.hvm_vcpu.mtrr;
+        struct hvm_hw_mtrr hw_mtrr = {
+            .msr_mtrr_def_type = mtrr_state->def_type |
+                                 (mtrr_state->enabled << 10),
+            .msr_mtrr_cap      = mtrr_state->mtrr_cap,
+        };
+        unsigned int i;
 
         hvm_get_guest_pat(v, &hw_mtrr.msr_pat_cr);
 
-        hw_mtrr.msr_mtrr_def_type = mtrr_state->def_type
-                                | (mtrr_state->enabled << 10);
-        hw_mtrr.msr_mtrr_cap = mtrr_state->mtrr_cap;
-
-        for ( i = 0; i < MTRR_VCNT; i++ )
+        for ( i = 0; i < MASK_EXTR(hw_mtrr.msr_mtrr_cap, MTRRcap_VCNT); i++ )
         {
             /* save physbase */
             hw_mtrr.msr_mtrr_var[i*2] =
@@ -726,6 +726,14 @@ static int hvm_load_mtrr_msr(struct domain *d, 
hvm_domain_context_t *h)
     if ( hvm_load_entry(MTRR, h, &hw_mtrr) != 0 )
         return -EINVAL;
 
+    if ( MASK_EXTR(hw_mtrr.msr_mtrr_cap, MTRRcap_VCNT) > MTRR_VCNT )
+    {
+        dprintk(XENLOG_G_ERR,
+                "HVM restore: %pv: too many (%lu) variable range MTRRs\n",
+                v, MASK_EXTR(hw_mtrr.msr_mtrr_cap, MTRRcap_VCNT));
+        return -EINVAL;
+    }
+
     mtrr_state = &v->arch.hvm_vcpu.mtrr;
 
     hvm_set_guest_pat(v, hw_mtrr.msr_pat_cr);
@@ -735,7 +743,7 @@ static int hvm_load_mtrr_msr(struct domain *d, 
hvm_domain_context_t *h)
     for ( i = 0; i < NUM_FIXED_MSR; i++ )
         mtrr_fix_range_msr_set(d, mtrr_state, i, hw_mtrr.msr_mtrr_fixed[i]);
 
-    for ( i = 0; i < MTRR_VCNT; i++ )
+    for ( i = 0; i < MASK_EXTR(hw_mtrr.msr_mtrr_cap, MTRRcap_VCNT); i++ )
     {
         mtrr_var_range_msr_set(d, mtrr_state,
                                MSR_IA32_MTRR_PHYSBASE(i),
-- 
2.17.0


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