libx86: introduce a helper to deserialise msr_policy objects

As with the serialise side, Xen's copy_from_guest API is used, with a
compatibility wrapper for the userspace build.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/include/xen/lib/x86/msr.h

@@ -48,6 +48,27 @@ typedef xen_msr_entry_t msr_entry_buffer_t[];
 int x86_msr_copy_to_buffer(const struct msr_policy *policy,
                            msr_entry_buffer_t msrs, uint32_t *nr_entries);
 
+/**
+ * Unserialise an msr_policy object from an array of msrs.
+ *
+ * @param policy     The msr_policy object to unserialise into.
+ * @param msrs       The array of msrs to unserialise from.
+ * @param nr_entries The number of entries in 'msrs'.
+ * @param err_msr    Optional hint filled on error.
+ * @returns -errno
+ *
+ * Reads at most MSR_MAX_SERIALISED_ENTRIES.  May fail for a number of reasons
+ * based on the content in an individual 'msrs' entry, including the MSR index
+ * not being valid in the policy, the flags field being nonzero, or if the
+ * value provided would truncate when stored in the policy.  In such cases,
+ * the optional err_* pointer is filled in to aid diagnostics.
+ *
+ * No content validation is performed on the data stored in the policy object.
+ */
+int x86_msr_copy_from_buffer(struct msr_policy *policy,
+                             const msr_entry_buffer_t msrs, uint32_t nr_entries,
+                             uint32_t *err_msr);
+
 #endif /* !XEN_LIB_X86_MSR_H */
 
 /*

xen/lib/x86/msr.c

@@ -47,6 +47,73 @@ int x86_msr_copy_to_buffer(const struct msr_policy *p,
     return 0;
 }
 
+int x86_msr_copy_from_buffer(struct msr_policy *p,
+                             const msr_entry_buffer_t msrs, uint32_t nr_entries,
+                             uint32_t *err_msr)
+{
+    unsigned int i;
+    xen_msr_entry_t data;
+    int rc;
+
+    /*
+     * A well formed caller is expected to pass an array with entries in
+     * order, and without any repetitions.  However, due to per-vendor
+     * differences, and in the case of upgrade or levelled scenarios, we
+     * typically expect fewer than MAX entries to be passed.
+     *
+     * Detecting repeated entries is prohibitively complicated, so we don't
+     * bother.  That said, one way or another if more than MAX entries are
+     * passed, something is wrong.
+     */
+    if ( nr_entries > MSR_MAX_SERIALISED_ENTRIES )
+        return -E2BIG;
+
+    for ( i = 0; i < nr_entries; i++ )
+    {
+        if ( copy_from_buffer_offset(&data, msrs, i, 1) )
+            return -EFAULT;
+
+        if ( data.flags ) /* .flags MBZ */
+        {
+            rc = -EINVAL;
+            goto err;
+        }
+
+        switch ( data.idx )
+        {
+            /*
+             * Assign data.val to p->field, checking for truncation if the
+             * backing storage for field is smaller than uint64_t
+             */
+#define ASSIGN(field)                             \
+({                                                \
+    if ( (typeof(p->field))data.val != data.val ) \
+    {                                             \
+        rc = -EOVERFLOW;                          \
+        goto err;                                 \
+    }                                             \
+    p->field = data.val;                          \
+})
+
+        case MSR_INTEL_PLATFORM_INFO: ASSIGN(plaform_info.raw); break;
+
+#undef ASSIGN
+
+        default:
+            rc = -ERANGE;
+            goto err;
+        }
+    }
+
+    return 0;
+
+ err:
+    if ( err_msr )
+        *err_msr = data.idx;
+
+    return rc;
+}
+
 /*
  * Local variables:
  * mode: C

xen/lib/x86/private.h

@@ -12,6 +12,7 @@
 #include <asm/msr-index.h>
 
 #define copy_to_buffer_offset copy_to_guest_offset
+#define copy_from_buffer_offset copy_from_guest_offset
 
 #else
 
@@ -44,6 +45,19 @@ static inline bool test_bit(unsigned int bit, const void *vaddr)
     0;                                                  \
 })
 
+/* memcpy(), but with copy_from_guest_offset()'s API. */
+#define copy_from_buffer_offset(dst, src, index, nr)    \
+({                                                      \
+    const typeof(*(src)) *src_ = (src);                 \
+    typeof(*(dst)) *dst_ = (dst);                       \
+    typeof(index) index_ = (index);                     \
+    typeof(nr) nr_ = (nr), i_;                          \
+                                                        \
+    for ( i_ = 0; i_ < nr_; i_++ )                      \
+        dst_[i_] = src_[index_ + i_];                   \
+    0;                                                  \
+})
+
 #endif /* __XEN__ */
 
 #endif /* XEN_LIB_X86_PRIVATE_H */