[xen stable-4.18] xen/livepatch: do Xen build-id check earlier

[patchbot@xxxxxxx]

commit aa057dbd3f36e195d8fc5a2c746079deb7105581
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Mon Nov 25 12:15:56 2024 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Nov 25 12:15:56 2024 +0100

    xen/livepatch: do Xen build-id check earlier
    
    The check against the expected Xen build ID should be done ahead of 
attempting
    to apply the alternatives contained in the livepatch.
    
    If the CPUID in the alternatives patching data is out of the scope of the
    running Xen featureset the BUG() in _apply_alternatives() will trigger thus
    bringing the system down.  Note the layout of struct alt_instr could also
    change between versions.  It's also possible for struct 
exception_table_entry
    to have changed format, hence leading to other kind of errors if parsing of 
the
    payload is done ahead of checking if the Xen build-id matches.
    
    Move the Xen build ID check as early as possible.  To do so introduce a new
    check_xen_buildid() function that parses and checks the Xen build-id before
    moving the payload.  Since the expected Xen build-id is used early to
    detect whether the livepatch payload could be loaded, there's no reason to
    store it in the payload struct, as a non-matching Xen build-id won't get the
    payload populated in the first place.
    
    Note printing the expected Xen build ID has part of dumping the payload
    information is no longer done: all loaded payloads would have Xen build IDs
    matching the running Xen, otherwise they would have failed to load.
    
    Fixes: 879615f5db1d ('livepatch: Always check hypervisor build ID upon 
livepatch upload')
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: fa49f4be413cdabde5b2264fc85d2710b15ea691
    master date: 2024-09-26 14:18:03 +0100
---
 xen/common/livepatch.c              | 86 +++++++++++++++++++++----------------
 xen/include/xen/livepatch_payload.h |  1 -
 2 files changed, 50 insertions(+), 37 deletions(-)

diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c
index b3655ec754..8578fefc02 100644
--- a/xen/common/livepatch.c
+++ b/xen/common/livepatch.c
@@ -448,28 +448,6 @@ static bool section_ok(const struct livepatch_elf *elf,
     return true;
 }
 
-static int xen_build_id_dep(const struct payload *payload)
-{
-    const void *id = NULL;
-    unsigned int len = 0;
-    int rc;
-
-    ASSERT(payload->xen_dep.len);
-    ASSERT(payload->xen_dep.p);
-
-    rc = xen_build_id(&id, &len);
-    if ( rc )
-        return rc;
-
-    if ( payload->xen_dep.len != len || memcmp(id, payload->xen_dep.p, len) ) {
-        printk(XENLOG_ERR LIVEPATCH "%s: check against hypervisor build-id 
failed\n",
-               payload->name);
-        return -EINVAL;
-    }
-
-    return 0;
-}
-
 /* Parses build-id sections into the given destination. */
 static int parse_buildid(const struct livepatch_elf_sec *sec,
                          struct livepatch_build_id *id)
@@ -495,11 +473,56 @@ static int parse_buildid(const struct livepatch_elf_sec 
*sec,
    return 0;
 }
 
+static int check_xen_buildid(const struct livepatch_elf *elf)
+{
+    const void *id;
+    unsigned int len;
+    struct livepatch_build_id lp_id;
+    const struct livepatch_elf_sec *sec =
+        livepatch_elf_sec_by_name(elf, ELF_LIVEPATCH_XEN_DEPENDS);
+    int rc;
+
+    if ( !sec )
+    {
+        printk(XENLOG_ERR LIVEPATCH "%s: section %s is missing\n",
+               elf->name, ELF_LIVEPATCH_XEN_DEPENDS);
+        return -EINVAL;
+    }
+
+    rc = parse_buildid(sec, &lp_id);
+    if ( rc )
+    {
+        printk(XENLOG_ERR LIVEPATCH
+               "%s: failed to parse section %s as build-id: %d\n",
+               elf->name, ELF_LIVEPATCH_XEN_DEPENDS, rc);
+        return -EINVAL;
+    }
+
+    rc = xen_build_id(&id, &len);
+    if ( rc )
+    {
+        printk(XENLOG_ERR LIVEPATCH
+               "%s: unable to get running Xen build-id: %d\n",
+               elf->name, rc);
+        return rc;
+    }
+
+    if ( lp_id.len != len || memcmp(id, lp_id.p, len) )
+    {
+        printk(XENLOG_ERR LIVEPATCH "%s: build-id mismatch:\n"
+                                    "Â  livepatch: %*phN\n"
+                                    "Â Â Â Â Â Â Â  xen: %*phN\n",
+               elf->name, lp_id.len, lp_id.p, len, id);
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
 static int check_special_sections(const struct livepatch_elf *elf)
 {
     unsigned int i;
     static const char *const names[] = { ELF_LIVEPATCH_DEPENDS,
-                                         ELF_LIVEPATCH_XEN_DEPENDS,
                                          ELF_BUILD_ID_NOTE};
     DECLARE_BITMAP(found, ARRAY_SIZE(names)) = { 0 };
 
@@ -768,12 +791,6 @@ static int prepare_payload(struct payload *payload,
     if ( rc )
         return rc;
 
-    rc = parse_buildid(livepatch_elf_sec_by_name(elf,
-                                                 ELF_LIVEPATCH_XEN_DEPENDS),
-                       &payload->xen_dep);
-    if ( rc )
-        return rc;
-
     /* Setup the virtual region with proper data. */
     region = &payload->region;
 
@@ -1083,6 +1100,10 @@ static int load_payload_data(struct payload *payload, 
void *raw, size_t len)
     if ( rc )
         goto out;
 
+    rc = check_xen_buildid(&elf);
+    if ( rc )
+       goto out;
+
     rc = move_payload(payload, &elf);
     if ( rc )
         goto out;
@@ -1107,10 +1128,6 @@ static int load_payload_data(struct payload *payload, 
void *raw, size_t len)
     if ( rc )
         goto out;
 
-    rc = xen_build_id_dep(payload);
-    if ( rc )
-        goto out;
-
     rc = build_symbol_table(payload, &elf);
     if ( rc )
         goto out;
@@ -2205,9 +2222,6 @@ static void cf_check livepatch_printall(unsigned char key)
 
         if ( data->dep.len )
             printk("depend-on=%*phN\n", data->dep.len, data->dep.p);
-
-        if ( data->xen_dep.len )
-            printk("depend-on-xen=%*phN\n", data->xen_dep.len, 
data->xen_dep.p);
     }
 
     spin_unlock(&payload_lock);
diff --git a/xen/include/xen/livepatch_payload.h 
b/xen/include/xen/livepatch_payload.h
index b9cd4f2096..43557fd96f 100644
--- a/xen/include/xen/livepatch_payload.h
+++ b/xen/include/xen/livepatch_payload.h
@@ -62,7 +62,6 @@ struct payload {
     unsigned int nsyms;                  /* Nr of entries in .strtab and 
symbols. */
     struct livepatch_build_id id;        /* ELFNOTE_DESC(.note.gnu.build-id) 
of the payload. */
     struct livepatch_build_id dep;       /* ELFNOTE_DESC(.livepatch.depends). 
*/
-    struct livepatch_build_id xen_dep;   /* 
ELFNOTE_DESC(.livepatch.xen_depends). */
     livepatch_loadcall_t *const *load_funcs;   /* The array of funcs to call 
after */
     livepatch_unloadcall_t *const *unload_funcs;/* load and unload of the 
payload. */
     struct livepatch_hooks hooks;        /* Pre and post hooks for apply and 
revert */
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.18