[PATCH v2 2/2] livepatch: refuse to resolve symbols that belong to init sections

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

Livepatch payloads containing symbols that belong to init sections can only
lead to page faults later on, as by the time the livepatch is loaded init
sections have already been freed.

Refuse to resolve such symbols and return an error instead.

Note such resolutions are only relevant for symbols that point to undefined
sections (SHN_UNDEF), as that implies the symbol is not in the current payload
and hence must either be a Xen or a different livepatch payload symbol.

Do not allow to resolve symbols that point to __init_begin, as that address is
also unmapped.  On the other hand, __init_end is not unmapped, and hence allow
resolutions against it.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Changes since v1:
 - Fix off-by-one in range checking.
---
 xen/common/livepatch_elf.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/xen/common/livepatch_elf.c b/xen/common/livepatch_elf.c
index 45d73912a3cd..a67101eadc02 100644
--- a/xen/common/livepatch_elf.c
+++ b/xen/common/livepatch_elf.c
@@ -4,6 +4,7 @@
 
 #include <xen/errno.h>
 #include <xen/lib.h>
+#include <xen/sections.h>
 #include <xen/symbols.h>
 #include <xen/livepatch_elf.h>
 #include <xen/livepatch.h>
@@ -310,6 +311,21 @@ int livepatch_elf_resolve_symbols(struct livepatch_elf 
*elf)
                     break;
                 }
             }
+
+            /*
+             * Ensure not an init symbol.  Only applicable to Xen symbols, as
+             * livepatch payloads don't have init sections or equivalent.
+             */
+            else if ( st_value >= (uintptr_t)&__init_begin &&
+                      st_value < (uintptr_t)&__init_end )
+            {
+                printk(XENLOG_ERR LIVEPATCH
+                       "%s: symbol %s is in init section, not resolving\n",
+                       elf->name, elf->sym[i].name);
+                rc = -ENXIO;
+                break;
+            }
+
             dprintk(XENLOG_DEBUG, LIVEPATCH "%s: Undefined symbol resolved: %s 
=> %#"PRIxElfAddr"\n",
                     elf->name, elf->sym[i].name, st_value);
             break;
-- 
2.44.0