From 8a7ddfca80850b5261a5552e0f4263d4997637cd Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Wed, 12 Oct 2022 18:43:48 +0200
Subject: [PATCH] exec: Use check_elf_image()

This allows exec to recover if an error should occur when loading the executable.

Thus, the calling process will be notified instead of killed.
---
 kernel/src/sys/exec.cpp | 40 ++++++++++++++++++----------------------
 1 file changed, 18 insertions(+), 22 deletions(-)

diff --git a/kernel/src/sys/exec.cpp b/kernel/src/sys/exec.cpp
index b7c1313f..c9663df5 100644
--- a/kernel/src/sys/exec.cpp
+++ b/kernel/src/sys/exec.cpp
@@ -26,6 +26,18 @@ void sys_exec(Context* context, const char* pathname)
         return;
     }
 
+    if (program->type == VFS_DIRECTORY)
+    {
+        context->rax = -EISDIR;
+        return;
+    }
+
+    if (ELFLoader::check_elf_image(program) < 0)
+    {
+        context->rax = -EINVAL; // FIXME: Should be ENOEXEC.
+        return;
+    }
+
     uint64_t allocated_stack = (uint64_t)MemoryManager::get_pages(TASK_PAGES_IN_STACK, MAP_READ_WRITE | MAP_USER);
     if (!allocated_stack)
     {
@@ -33,28 +45,6 @@ void sys_exec(Context* context, const char* pathname)
         return;
     }
 
-    char* kpathname = strdup(
-        pathname); // Since we are going to free the original task's memory, we cannot use anything coming from it.
-
-    // FIXME: This should be done later, but since there is a very high chance that loading the executed program's
-    // ELF image will overwrite ours, we have to do it here.
-    ELFLoader::release_elf_image(Scheduler::current_task()->image);
-
-    // FIXME: Check the ELF image is valid before loading it into memory. This will allow us to first check, then free
-    // the previous image, then load, which should reduce the chances of loading failing to almost zero.
-    ELFImage* image = ELFLoader::load_elf_from_filesystem(kpathname);
-    if (!image)
-    {
-        MemoryManager::release_pages((void*)allocated_stack, TASK_PAGES_IN_STACK);
-        Scheduler::current_task()->image = nullptr;
-        kfree(kpathname);
-        kerrorln("exec(): ERROR: Failed to load program. Previous program has already been freed, thus cannot "
-                 "return to it.");
-        return Scheduler::task_exit(context, -255);
-    }
-
-    kfree(kpathname);
-
     Interrupts::disable();
     ASSERT(!Interrupts::are_enabled()); // This part is pretty sensitive.
 
@@ -63,6 +53,12 @@ void sys_exec(Context* context, const char* pathname)
 
     // At this point, pretty much nothing can fail.
 
+    ELFLoader::release_elf_image(Scheduler::current_task()->image);
+
+    ELFImage* image = ELFLoader::load_elf_from_vfs(program);
+    ASSERT(image); // If check_elf_image succeeded, load_elf_from_vfs MUST succeed, unless something has gone terribly
+                   // wrong.
+
     MemoryManager::release_pages((void*)task->allocated_stack, TASK_PAGES_IN_STACK);
 
     task->allocated_stack = allocated_stack;