[PATCH v4 6/6] efi: restrict arm/arm64 linux loader initrd placement

[Leif Lindholm]

The 32-bit arm Linux kernel is built as a zImage, which self-decompresses
down to near start of RAM. In order for an initrd/initramfs to be
accessible, it needs to be placed within the first ~768MB of RAM.
The initrd loader built into the kernel EFI stub restricts this down to
512MB for simplicity - so enable the same restriction in grub.

For arm64, the requirement is within a 1GB aligned 32GB window also
covering the (runtime) kernel image. Since the EFI stub loader itself
will attempt to relocate to near start of RAM, force initrd to be loaded
completely within the first 32GB of RAM.

Signed-off-by: Leif Lindholm <address@hidden>
---
 grub-core/loader/arm64/linux.c | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
index f90c5f926..1f86229f8 100644
--- a/grub-core/loader/arm64/linux.c
+++ b/grub-core/loader/arm64/linux.c
@@ -193,6 +193,42 @@ grub_linux_unload (void)
   return GRUB_ERR_NONE;
 }
 
+/*
+ * As per linux/Documentation/arm/Booting
+ * ARM initrd needs to be covered by kernel linear mapping,
+ * so place it in the first 512MB of DRAM.
+ *
+ * As per linux/Documentation/arm64/booting.txt
+ * ARM64 initrd needs to be contained entirely within a 1GB aligned window
+ * of up to 32GB of size that covers the kernel image as well.
+ * Since the EFI stub loader will attempt to load the kernel near start of
+ * RAM, place the buffer in the first 32GB of RAM.
+ */
+#ifdef __arm__
+#define INITRD_MAX_ADDRESS_OFFSET (512U * 1024 * 1024)
+#else /* __aarch64__ */
+#define INITRD_MAX_ADDRESS_OFFSET (32ULL * 1024 * 1024 * 1024)
+#endif
+
+/*
+ * This function returns a pointer to a legally allocated initrd buffer,
+ * or NULL if unsuccessful
+ */
+static void *
+allocate_initrd_mem (int initrd_pages)
+{
+  grub_addr_t max_addr;
+
+  if (grub_efi_get_ram_base (&max_addr) != GRUB_ERR_NONE)
+    return NULL;
+
+  max_addr += INITRD_MAX_ADDRESS_OFFSET - 1;
+
+  return grub_efi_allocate_pages_real (max_addr, initrd_pages,
+                                      GRUB_EFI_ALLOCATE_MAX_ADDRESS,
+                                      GRUB_EFI_LOADER_DATA);
+}
+
 static grub_err_t
 grub_cmd_initrd (grub_command_t cmd __attribute__ ((unused)),
                 int argc, char *argv[])
@@ -221,7 +257,8 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ 
((unused)),
   grub_dprintf ("linux", "Loading initrd\n");
 
   initrd_pages = (GRUB_EFI_BYTES_TO_PAGES (initrd_size));
-  initrd_mem = grub_efi_allocate_any_pages (initrd_pages);
+  initrd_mem = allocate_initrd_mem (initrd_pages);
+
   if (!initrd_mem)
     {
       grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("out of memory"));
-- 
2.11.0