xen/livepatch: fix norevert test attempt to open-code revert

The purpose of the norevert test is to install a dummy handler that replaces
the internal Xen revert code, and then perform the revert in the post-revert
hook.  For that purpose the usage of the previous common_livepatch_revert() is
not enough, as that just reverts specific functions, but not the whole state of
the payload.

Remove both common_livepatch_{apply,revert}() and instead expose
revert_payload{,_tail}() in order to perform the patch revert from the
post-revert hook.

Fixes: 6047104c3c ('livepatch: Add per-function applied/reverted state tracking marker')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Ross Lagerwall <ross.lagerwall@citrix.com>
master commit: cdae267ce1
master date: 2024-02-28 16:57:25 +0000

xen/common/livepatch.c

@@ -1366,7 +1366,22 @@ static int apply_payload(struct payload *data)
     ASSERT(!local_irq_is_enabled());
 
     for ( i = 0; i < data->nfuncs; i++ )
-        common_livepatch_apply(&data->funcs[i], &data->fstate[i]);
+    {
+        const struct livepatch_func *func = &data->funcs[i];
+        struct livepatch_fstate *state = &data->fstate[i];
+
+        /* If the action has been already executed on this function, do nothing. */
+        if ( state->applied == LIVEPATCH_FUNC_APPLIED )
+        {
+            printk(XENLOG_WARNING LIVEPATCH
+                   "%s: %s has been already applied before\n",
+                   __func__, func->name);
+            continue;
+        }
+
+        arch_livepatch_apply(func, state);
+        state->applied = LIVEPATCH_FUNC_APPLIED;
+    }
 
     arch_livepatch_revive();
 
@@ -1382,7 +1397,7 @@ static inline void apply_payload_tail(struct payload *data)
     data->state = LIVEPATCH_STATE_APPLIED;
 }
 
-static int revert_payload(struct payload *data)
+int revert_payload(struct payload *data)
 {
     unsigned int i;
     int rc;
@@ -1397,7 +1412,25 @@ static int revert_payload(struct payload *data)
     }
 
     for ( i = 0; i < data->nfuncs; i++ )
-        common_livepatch_revert(&data->funcs[i], &data->fstate[i]);
+    {
+        const struct livepatch_func *func = &data->funcs[i];
+        struct livepatch_fstate *state = &data->fstate[i];
+
+        /*
+         * If the apply action hasn't been executed on this function, do
+         * nothing.
+         */
+        if ( !func->old_addr || state->applied == LIVEPATCH_FUNC_NOT_APPLIED )
+        {
+            printk(XENLOG_WARNING LIVEPATCH
+                   "%s: %s has not been applied before\n",
+                   __func__, func->name);
+            continue;
+        }
+
+        arch_livepatch_revert(func, state);
+        state->applied = LIVEPATCH_FUNC_NOT_APPLIED;
+    }
 
     /*
      * Since we are running with IRQs disabled and the hooks may call common
@@ -1415,7 +1448,7 @@ static int revert_payload(struct payload *data)
     return 0;
 }
 
-static inline void revert_payload_tail(struct payload *data)
+void revert_payload_tail(struct payload *data)
 {
     list_del(&data->applied_list);
 

xen/include/xen/livepatch.h

@@ -136,35 +136,11 @@ void arch_livepatch_post_action(void);
 void arch_livepatch_mask(void);
 void arch_livepatch_unmask(void);
 
-static inline void common_livepatch_apply(const struct livepatch_func *func,
-                                          struct livepatch_fstate *state)
-{
-    /* If the action has been already executed on this function, do nothing. */
-    if ( state->applied == LIVEPATCH_FUNC_APPLIED )
-    {
-        printk(XENLOG_WARNING LIVEPATCH "%s: %s has been already applied before\n",
-                __func__, func->name);
-        return;
-    }
+/* Only for testing purposes. */
+struct payload;
+int revert_payload(struct payload *data);
+void revert_payload_tail(struct payload *data);
 
-    arch_livepatch_apply(func, state);
-    state->applied = LIVEPATCH_FUNC_APPLIED;
-}
-
-static inline void common_livepatch_revert(const struct livepatch_func *func,
-                                           struct livepatch_fstate *state)
-{
-    /* If the apply action hasn't been executed on this function, do nothing. */
-    if ( !func->old_addr || state->applied == LIVEPATCH_FUNC_NOT_APPLIED )
-    {
-        printk(XENLOG_WARNING LIVEPATCH "%s: %s has not been applied before\n",
-                __func__, func->name);
-        return;
-    }
-
-    arch_livepatch_revert(func, state);
-    state->applied = LIVEPATCH_FUNC_NOT_APPLIED;
-}
 #else
 
 /*

xen/test/livepatch/xen_action_hooks_norevert.c

@@ -96,26 +96,14 @@ static int revert_hook(livepatch_payload_t *payload)
 
 static void post_revert_hook(livepatch_payload_t *payload)
 {
-    int i;
+    unsigned long flags;
 
     printk(KERN_DEBUG "%s: Hook starting.\n", __func__);
 
-    for (i = 0; i < payload->nfuncs; i++)
-    {
-        const struct livepatch_func *func = &payload->funcs[i];
-        struct livepatch_fstate *fstate = &payload->fstate[i];
-
-        BUG_ON(revert_cnt != 1);
-        BUG_ON(fstate->applied != LIVEPATCH_FUNC_APPLIED);
-
-        /* Outside of quiesce zone: MAY TRIGGER HOST CRASH/UNDEFINED BEHAVIOR */
-        arch_livepatch_quiesce();
-        common_livepatch_revert(payload);
-        arch_livepatch_revive();
-        BUG_ON(fstate->applied == LIVEPATCH_FUNC_APPLIED);
-
-        printk(KERN_DEBUG "%s: post reverted: %s\n", __func__, func->name);
-    }
+    local_irq_save(flags);
+    BUG_ON(revert_payload(payload));
+    revert_payload_tail(payload);
+    local_irq_restore(flags);
 
     printk(KERN_DEBUG "%s: Hook done.\n", __func__);
 }