Re: [Xen-devel] [PATCH v3 01/12] livepatch: Always check hypervisor build ID upon hotpatch upload

["Wieczorkiewicz, Pawel" <wipawel@xxxxxxxxx>]

On 16. Sep 2019, at 18:23, Ross Lagerwall <ross.lagerwall@xxxxxxxxxx> wrote:

On 9/16/19 11:59 AM, Pawel Wieczorkiewicz wrote:

This change is part of a independant stacked hotpatch modules
feature. This feature allows to bypass dependencies between modules
upon loading, but still verifies Xen build ID matching.
In order to prevent (up)loading any hotpatches built for different
hypervisor version as indicated by the Xen Build ID, add checking for
the payload's vs Xen's build id match.
To achieve that embed into every hotpatch another section with a
dedicated hypervisor build id in it. After the payload is loaded and
the .livepatch.xen_depends section becomes available, perform the
check and reject the payload if there is no match.

snip

+    sec = livepatch_elf_sec_by_name(elf, ELF_LIVEPATCH_XEN_DEPENDS);
+    if ( sec )
+    {
+        n = sec->load_addr;
+
+        if ( sec->sec->sh_size <= sizeof(*n) )
+            return -EINVAL;
+
+        if ( xen_build_id_check(n, sec->sec->sh_size,
+                                &payload->xen_dep.p, &payload->xen_dep.len) )
+            return -EINVAL;
+
+        if ( !payload->xen_dep.len || !payload->xen_dep.p )
+            return -EINVAL;
+    }
+
     /* Setup the virtual region with proper data. */
     region = &payload->region;
 @@ -882,6 +922,10 @@ static int load_payload_data(struct payload *payload, void *raw, size_t len)
     if ( rc )
         goto out;
 +    rc = check_xen_build_id(payload);
+    if ( rc )
+        goto out;
+
     rc = build_symbol_table(payload, &elf);
     if ( rc )
         goto out;

It is a bit confusing having a new function called check_xen_build_id() when there is already a xen_build_id_check(). Perhaps the new one should be called xen_build_id_dep() as it is analogous to the existing build_id_dep()?

Yes, that definitely makes sense. I will squash it into v4. Otherwise, I hope it can be fixed upon merging.

Either way,

Reviewed-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

Many thanks!

Best Regards,
Pawel Wieczorkiewicz

Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Ralf Herbrich
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel