From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Fri, 27 Mar 2020 11:59:02 +0000 (+0000)
Subject: x86/ucode/amd: Fix potential buffer overrun with equiv table handling
X-Git-Tag: archive/raspbian/4.14.0+80-gd101b417b7-1+rpi1^2~63^2~484
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=1f97b6b9f1b5978659c5735954c37c130e7bb151;p=xen.git

x86/ucode/amd: Fix potential buffer overrun with equiv table handling

find_equiv_cpu_id() loops until it finds a 0 installed_cpu entry.  Well formed
AMD microcode containers have this property.

Extend the checking in install_equiv_cpu_table() to reject tables which don't
have a sentinal at the end.

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

diff --git a/xen/arch/x86/cpu/microcode/amd.c b/xen/arch/x86/cpu/microcode/amd.c
index 122b8309af..96b80ff960 100644
--- a/xen/arch/x86/cpu/microcode/amd.c
+++ b/xen/arch/x86/cpu/microcode/amd.c
@@ -309,6 +309,7 @@ static int install_equiv_cpu_table(
     size_t *offset)
 {
     const struct mpbhdr *mpbuf = data + *offset + 4;
+    const struct equiv_cpu_entry *eq;
 
     *offset += mpbuf->len + CONT_HDR_SIZE;	/* add header length */
 
@@ -318,7 +319,9 @@ static int install_equiv_cpu_table(
         return -EINVAL;
     }
 
-    if ( mpbuf->len == 0 )
+    if ( mpbuf->len == 0 || mpbuf->len % sizeof(*eq) ||
+         (eq = (const void *)mpbuf->data,
+          eq[(mpbuf->len / sizeof(*eq)) - 1].installed_cpu) )
     {
         printk(KERN_ERR "microcode: Wrong microcode equivalent cpu table length\n");
         return -EINVAL;