Re: [PATCH-4.16 v2] xen/efi: Fix Grub2 boot on arm64

[Stefano Stabellini <sstabellini@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 8686 bytes --]

On Thu, 4 Nov 2021, Jan Beulich wrote:
> On 04.11.2021 15:12, Luca Fancellu wrote:
> > --- a/xen/common/efi/boot.c
> > +++ b/xen/common/efi/boot.c
> > @@ -449,6 +449,15 @@ static EFI_FILE_HANDLE __init get_parent_handle(EFI_LOADED_IMAGE *loaded_image,
> >      CHAR16 *pathend, *ptr;
> >      EFI_STATUS ret;
> >  
> > +    /*
> > +     * Grub2 running on top of EDK2 has been observed to supply a NULL
> > +     * DeviceHandle. We can't use that to gain access to the filesystem.
> > +     * However the system can still boot if it doesn’t require access to the
> > +     * filesystem.
> > +     */
> > +    if ( !loaded_image->DeviceHandle )
> > +        return NULL;
> > +
> >      do {
> >          EFI_FILE_IO_INTERFACE *fio;
> >  
> > @@ -581,6 +590,8 @@ static bool __init read_file(EFI_FILE_HANDLE dir_handle, CHAR16 *name,
> >      EFI_STATUS ret;
> >      const CHAR16 *what = NULL;
> >  
> > +    if ( !dir_handle )
> > +        blexit(L"Error: No access to the filesystem");
> >      if ( !name )
> >          PrintErrMesg(L"No filename", EFI_OUT_OF_RESOURCES);
> >      ret = dir_handle->Open(dir_handle, &FileHandle, name,
> > @@ -1333,8 +1344,18 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
> >              EFI_FILE_HANDLE handle = get_parent_handle(loaded_image,
> >                                                         &file_name);
> >  
> > -            handle->Close(handle);
> > -            *argv = file_name;
> > +            if ( !handle )
> > +            {
> > +                PrintErr(L"Error retrieving image name: no filesystem access."
> > +                         L" Setting default to xen.efi");
> > +                PrintErr(newline);
> > +                *argv = L"xen.efi";
> > +            }
> > +            else
> > +            {
> > +                handle->Close(handle);
> > +                *argv = file_name;
> > +            }
> >          }
> >  
> >          name.s = get_value(&cfg, section.s, "options");
> > @@ -1369,7 +1390,8 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
> >      /* Get the number of boot modules specified on the DT or an error (<0) */
> >      dt_modules_found = efi_check_dt_boot(dir_handle);
> >  
> > -    dir_handle->Close(dir_handle);
> > +    if ( dir_handle )
> > +        dir_handle->Close(dir_handle);
> >  
> >      if ( dt_modules_found < 0 )
> >          /* efi_check_dt_boot throws some error */
> > 
> 
> I'm sorry, but I think we need to take a step back here and revisit
> the earlier change. If that hadn't moved obtaining dir_handle out by
> one level of scope, nothing bad would have happened to the case that
> you're now trying to fix, I understand? So perhaps that part wants
> undoing, with efi_check_dt_boot() instead getting passed loaded_image.
> That way, down the call tree the needed handle can be obtained via
> another call to get_parent_handle(), and quite likely in the scenario
> you're trying to fix here execution wouldn't even make it there. This
> then wouldn't be much different to the image name retrieval calling
> get_parent_handle() a 2nd time, rather than trying to re-use
> dir_handle.
> 
> Net effect being that I think get_parent_handle() would then again
> only be called when the returned handle is actually needed, and hence
> when failure of HandleProtocol() (for DeviceHandle being NULL just
> like for any other reason) is indeed an error that needs reporting.

In my opinion the current version is good enough. Regardless, I looked
at your suggestion into details. As it took me some time to understand
it, I thought I would share the code changes that I think correspond to
what you wrote. Does everything check out?

If so, I think it looks fine, maybe a bit better than the current
version. I'll leave that to you and Luca.


diff --git a/xen/arch/arm/efi/efi-boot.h b/xen/arch/arm/efi/efi-boot.h
index c3ae9751ab..9dcd8547cd 100644
--- a/xen/arch/arm/efi/efi-boot.h
+++ b/xen/arch/arm/efi/efi-boot.h
@@ -8,6 +8,8 @@
 #include <asm/setup.h>
 #include <asm/smp.h>
 
+extern EFI_FILE_HANDLE __init get_parent_handle(EFI_LOADED_IMAGE *loaded_image,
+                                                CHAR16 **leaf);
 typedef struct {
     char *name;
     unsigned int name_len;
@@ -54,7 +56,7 @@ static int handle_module_node(EFI_FILE_HANDLE dir_handle,
                               bool is_domu_module);
 static int handle_dom0less_domain_node(EFI_FILE_HANDLE dir_handle,
                                        int domain_node);
-static int efi_check_dt_boot(EFI_FILE_HANDLE dir_handle);
+static int efi_check_dt_boot(EFI_LOADED_IMAGE *loaded_image);
 
 #define DEVICE_TREE_GUID \
 {0xb1b621d5, 0xf19c, 0x41a5, {0x83, 0x0b, 0xd9, 0x15, 0x2c, 0x69, 0xaa, 0xe0}}
@@ -851,10 +853,14 @@ static int __init handle_dom0less_domain_node(EFI_FILE_HANDLE dir_handle,
  * dom0 and domU guests to be loaded.
  * Returns the number of multiboot modules found or a negative number for error.
  */
-static int __init efi_check_dt_boot(EFI_FILE_HANDLE dir_handle)
+static int __init efi_check_dt_boot(EFI_LOADED_IMAGE *loaded_image)
 {
     int chosen, node, addr_len, size_len;
     unsigned int i = 0, modules_found = 0;
+    EFI_FILE_HANDLE dir_handle;
+    CHAR16 *file_name;
+
+    dir_handle = get_parent_handle(loaded_image, &file_name);
 
     /* Check for the chosen node in the current DTB */
     chosen = setup_chosen_node(fdt, &addr_len, &size_len);
@@ -895,6 +901,8 @@ static int __init efi_check_dt_boot(EFI_FILE_HANDLE dir_handle)
         efi_bs->FreePool(modules[i].name);
     }
 
+    dir_handle->Close(dir_handle);
+
     return modules_found;
 }
 
diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
index 112b7e7571..2407671a7d 100644
--- a/xen/common/efi/boot.c
+++ b/xen/common/efi/boot.c
@@ -167,7 +167,7 @@ static void __init PrintErr(const CHAR16 *s)
 }
 
 #ifndef CONFIG_HAS_DEVICE_TREE
-static int __init efi_check_dt_boot(EFI_FILE_HANDLE dir_handle)
+static int __init efi_check_dt_boot(EFI_LOADED_IMAGE *loaded_image)
 {
     return 0;
 }
@@ -439,8 +439,8 @@ static unsigned int __init get_argv(unsigned int argc, CHAR16 **argv,
     return argc;
 }
 
-static EFI_FILE_HANDLE __init get_parent_handle(EFI_LOADED_IMAGE *loaded_image,
-                                                CHAR16 **leaf)
+EFI_FILE_HANDLE __init get_parent_handle(EFI_LOADED_IMAGE *loaded_image,
+                                         CHAR16 **leaf)
 {
     static EFI_GUID __initdata fs_protocol = SIMPLE_FILE_SYSTEM_PROTOCOL;
     static CHAR16 __initdata buffer[512];
@@ -1236,9 +1236,6 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
 
     efi_arch_relocate_image(0);
 
-    /* Get the file system interface. */
-    dir_handle = get_parent_handle(loaded_image, &file_name);
-
     if ( use_cfg_file )
     {
         UINTN depth, cols, rows, size;
@@ -1251,6 +1248,9 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
 
         gop = efi_get_gop();
 
+        /* Get the file system interface. */
+        dir_handle = get_parent_handle(loaded_image, &file_name);
+
         /* Read and parse the config file. */
         if ( read_section(loaded_image, L"config", &cfg, NULL) )
             PrintStr(L"Using builtin config file\r\n");
@@ -1344,18 +1344,8 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
             EFI_FILE_HANDLE handle = get_parent_handle(loaded_image,
                                                        &file_name);
 
-            if ( !handle )
-            {
-                PrintErr(L"Error retrieving image name: no filesystem access."
-                         L" Setting default to xen.efi");
-                PrintErr(newline);
-                *argv = L"xen.efi";
-            }
-            else
-            {
-                handle->Close(handle);
-                *argv = file_name;
-            }
+            handle->Close(handle);
+            *argv = file_name;
         }
 
         name.s = get_value(&cfg, section.s, "options");
@@ -1383,15 +1373,14 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable)
         efi_bs->FreePages(cfg.addr, PFN_UP(cfg.size));
         cfg.addr = 0;
 
+        dir_handle->Close(dir_handle);
+
         if ( gop && !base_video )
             gop_mode = efi_find_gop_mode(gop, cols, rows, depth);
     }
 
     /* Get the number of boot modules specified on the DT or an error (<0) */
-    dt_modules_found = efi_check_dt_boot(dir_handle);
-
-    if ( dir_handle )
-        dir_handle->Close(dir_handle);
+    dt_modules_found = efi_check_dt_boot(loaded_image);
 
     if ( dt_modules_found < 0 )
         /* efi_check_dt_boot throws some error */