File 5e84905c-x86-ucode-AMD-fix-more-potential-buffer-overruns.patch of Package xen.14764

# Commit 718d1432000079ea7120f6cb770372afe707ce27
# Date 2020-04-01 14:00:12 +0100
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
x86/ucode/amd: Fix more potential buffer overruns with microcode parsing

cpu_request_microcode() doesn't know the buffer is at least 4 bytes long
before inspecting UCODE_MAGIC.

install_equiv_cpu_table() doesn't know the boundary of the buffer it is
interpreting as an equivalency table.  This case was clearly observed at one
point in the past, given the subsequent overrun detection, but without
comprehending that the damage was already done.

Make the logic consistent with container_fast_forward() and pass size_left in
to install_equiv_cpu_table().

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -294,11 +294,20 @@ static int get_ucode_from_buffer_amd(
 static int install_equiv_cpu_table(
     struct microcode_amd *mc_amd,
     const void *data,
+    size_t size_left,
     size_t *offset)
 {
-    const struct mpbhdr *mpbuf = data + *offset + 4;
+    const struct mpbhdr *mpbuf;
     const struct equiv_cpu_entry *eq;
 
+    if ( size_left < (sizeof(*mpbuf) + 4) ||
+         (mpbuf = data + *offset + 4,
+          size_left - sizeof(*mpbuf) - 4 < mpbuf->len) )
+    {
+        printk(XENLOG_WARNING "microcode: No space for equivalent cpu table\n");
+        return -EINVAL;
+    }
+
     *offset += mpbuf->len + CONT_HDR_SIZE;	/* add header length */
 
     if ( mpbuf->type != UCODE_EQUIV_CPU_TABLE_TYPE )
@@ -413,7 +422,7 @@ static int cpu_request_microcode(unsigne
 
     current_cpu_id = cpuid_eax(0x00000001);
 
-    if ( *(const uint32_t *)buf != UCODE_MAGIC )
+    if ( bufsize < 4 || *(const uint32_t *)buf != UCODE_MAGIC )
     {
         printk(KERN_ERR "microcode: Wrong microcode patch file magic\n");
         error = -EINVAL;
@@ -443,24 +452,13 @@ static int cpu_request_microcode(unsigne
      */
     while ( offset < bufsize )
     {
-        error = install_equiv_cpu_table(mc_amd, buf, &offset);
+        error = install_equiv_cpu_table(mc_amd, buf, bufsize - offset, &offset);
         if ( error )
         {
             printk(KERN_ERR "microcode: installing equivalent cpu table failed\n");
             break;
         }
 
-        /*
-         * Could happen as we advance 'offset' early
-         * in install_equiv_cpu_table
-         */
-        if ( offset > bufsize )
-        {
-            printk(KERN_ERR "microcode: Microcode buffer overrun\n");
-            error = -EINVAL;
-            break;
-        }
-
         if ( find_equiv_cpu_id(mc_amd->equiv_cpu_table, current_cpu_id,
                                &equiv_cpu_id) )
             break;