[PATCH RH grub2] arm64: Fix EFI loader kernel image allocation

[Benjamin Herrenschmidt]

We are currently allocating just enough memory for the file size,
which means that the kernel BSS is in limbo (and not even zeroed).

Instead, use the PE optional header in which the kernel puts the
actual size it needs, including BSS, and make sure we clear it.

Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
---

This bug comes with the original shim_lock patch which removes LoadImage/StartImage
and directly calls into the loaded image instead. It has been observbed to
occasionally cause boot failures on EC2 ARM instances.

I know at least Fedora/RH (and thus Amazon Linux 2) and Ubuntu are affected.

 grub-core/loader/arm64/linux.c | 82 ++++++++++++++++++++++------------
 1 file changed, 54 insertions(+), 28 deletions(-)

diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
index 47f8cf0d8..f568d452d 100644
--- a/grub-core/loader/arm64/linux.c
+++ b/grub-core/loader/arm64/linux.c
@@ -311,14 +311,31 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ ((unused)),
   return grub_errno;
 }
 
+static grub_err_t
+parse_pe_header (void *kernel, grub_uint64_t *total_size, grub_uint32_t *entry_offset)
+{
+  struct linux_arch_kernel_header *lh = kernel;
+  struct grub_armxx_linux_pe_header *pe;
+
+  pe = (void *)((unsigned long)kernel + lh->hdr_offset);
+
+  if (pe->opt.magic != GRUB_PE32_PE64_MAGIC)
+    return grub_error(GRUB_ERR_BAD_OS, "Invalid PE optional header magic");
+
+  *total_size   = pe->opt.image_size;
+  *entry_offset = pe->opt.entry_addr;
+
+  return GRUB_ERR_NONE;
+}
+
 static grub_err_t
 grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
 		int argc, char *argv[])
 {
   grub_file_t file = 0;
-  struct linux_arch_kernel_header lh;
-  struct grub_armxx_linux_pe_header *pe;
   grub_err_t err;
+  grub_uint64_t filelen;
+  void *kernel = NULL;
   int rc;
 
   grub_dl_ref (my_mod);
@@ -333,40 +350,24 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
   if (!file)
     goto fail;
 
-  kernel_size = grub_file_size (file);
-
-  if (grub_file_read (file, &lh, sizeof (lh)) < (long) sizeof (lh))
-    return grub_errno;
-
-  if (grub_arch_efi_linux_check_image (&lh) != GRUB_ERR_NONE)
-    goto fail;
-
-  grub_loader_unset();
-
-  grub_dprintf ("linux", "kernel file size: %lld\n", (long long) kernel_size);
-  kernel_addr = grub_efi_allocate_any_pages (GRUB_EFI_BYTES_TO_PAGES (kernel_size));
-  grub_dprintf ("linux", "kernel numpages: %lld\n",
-		(long long) GRUB_EFI_BYTES_TO_PAGES (kernel_size));
-  if (!kernel_addr)
+  filelen = grub_file_size (file);
+  kernel = grub_malloc(filelen);
+  if (!kernel)
     {
-      grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("out of memory"));
+      grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("cannot allocate kernel load buffer"));
       goto fail;
     }
 
-  grub_file_seek (file, 0);
-  if (grub_file_read (file, kernel_addr, kernel_size)
-      < (grub_int64_t) kernel_size)
+  if (grub_file_read (file, kernel, filelen) < filelen)
     {
-      if (!grub_errno)
-	grub_error (GRUB_ERR_BAD_OS, N_("premature end of file %s"), argv[0]);
+      grub_error (GRUB_ERR_FILE_READ_ERROR, N_("Can't read kernel %s"),
+		  argv[0]);
       goto fail;
     }
 
-  grub_dprintf ("linux", "kernel @ %p\n", kernel_addr);
-
   if (grub_efi_get_secureboot () == GRUB_EFI_SECUREBOOT_MODE_ENABLED)
     {
-      rc = grub_linuxefi_secure_validate (kernel_addr, kernel_size);
+      rc = grub_linuxefi_secure_validate (kernel, filelen);
       if (rc <= 0)
 	{
 	  grub_error (GRUB_ERR_INVALID_COMMAND,
@@ -375,8 +376,30 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
 	}
     }
 
-  pe = (void *)((unsigned long)kernel_addr + lh.hdr_offset);
-  handover_offset = pe->opt.entry_addr;
+  if (grub_arch_efi_linux_check_image (kernel) != GRUB_ERR_NONE)
+    goto fail;
+  if (parse_pe_header (kernel, &kernel_size, &handover_offset) != GRUB_ERR_NONE)
+    goto fail;
+  grub_dprintf ("linux", "kernel mem size     : %lld\n", (long long) kernel_size);
+  grub_dprintf ("linux", "kernel entry offset : %d\n", handover_offset);
+
+  grub_loader_unset();
+
+  kernel_addr = grub_efi_allocate_any_pages (GRUB_EFI_BYTES_TO_PAGES (kernel_size));
+  grub_dprintf ("linux", "kernel numpages: %lld\n",
+		(long long) GRUB_EFI_BYTES_TO_PAGES (kernel_size));
+  if (!kernel_addr)
+    {
+      grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("out of memory"));
+      goto fail;
+    }
+
+  grub_dprintf ("linux", "kernel @ %p\n", kernel_addr);
+  grub_memcpy (kernel_addr, kernel, grub_min(filelen, kernel_size));
+  if (kernel_size > filelen)
+    grub_memset ((char *)kernel_addr + filelen, 0, kernel_size - filelen);
+  grub_free(kernel);
+  kernel = NULL;
 
   cmdline_size = grub_loader_cmdline_size (argc, argv) + sizeof (LINUX_IMAGE);
   linux_args = grub_malloc (cmdline_size);
@@ -400,6 +423,9 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
     }
 
 fail:
+  if (kernel)
+    grub_free (kernel);
+
   if (file)
     grub_file_close (file);