[PATCH] 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.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/common/livepatch_elf.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/xen/common/livepatch_elf.c b/xen/common/livepatch_elf.c
index 45d73912a3cd..25b81189c590 100644
--- a/xen/common/livepatch_elf.c
+++ b/xen/common/livepatch_elf.c
@@ -8,6 +8,9 @@
 #include <xen/livepatch_elf.h>
 #include <xen/livepatch.h>
 
+/* Needed to check we don't resolve against init section symbols. */
+extern char __init_begin[], __init_end[];
+
 const struct livepatch_elf_sec *
 livepatch_elf_sec_by_name(const struct livepatch_elf *elf,
                           const char *name)
@@ -310,6 +313,20 @@ 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