efi/arm-stub: Correct FDT and initrd allocation rules for arm64

On arm64, we have made some changes over the past year to the way the
kernel itself is allocated and to how it deals with the initrd and FDT.
This patch brings the allocation logic in the EFI stub in line with that,
which is necessary because the introduction of KASLR has created the
possibility for the initrd to be allocated in a place where the kernel
may not be able to map it. (This is mostly a theoretical scenario, since
it only affects systems where the physical memory footprint exceeds the
size of the linear mapping.)

Since we know the kernel itself will be covered by the linear mapping,
choose a suitably sized window (i.e., based on the size of the linear
region) covering the kernel when allocating memory for the initrd.

The FDT may be anywhere in memory on arm64 now that we map it via the
fixmap, so we can lift the address restriction there completely.

Tested-by: Richard Ruigrok <rruigrok@codeaurora.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170404160245.27812-4-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/arm/include/asm/efi.h

@@ -85,6 +85,18 @@ static inline void efifb_setup_from_dmi(struct screen_info *si, const char *opt)
  */
 #define ZIMAGE_OFFSET_LIMIT	SZ_128M
 #define MIN_ZIMAGE_OFFSET	MAX_UNCOMP_KERNEL_SIZE
-#define MAX_FDT_OFFSET		ZIMAGE_OFFSET_LIMIT
+
+/* on ARM, the FDT should be located in the first 128 MB of RAM */
+static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base)
+{
+	return dram_base + ZIMAGE_OFFSET_LIMIT;
+}
+
+/* on ARM, the initrd should be loaded in a lowmem region */
+static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
+						    unsigned long image_addr)
+{
+	return dram_base + SZ_512M;
+}
 
 #endif /* _ASM_ARM_EFI_H */

arch/arm64/include/asm/efi.h

@@ -46,7 +46,28 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);
  * 2MiB so we know it won't cross a 2MiB boundary.
  */
 #define EFI_FDT_ALIGN	SZ_2M   /* used by allocate_new_fdt_and_exit_boot() */
-#define MAX_FDT_OFFSET	SZ_512M
+
+/* on arm64, the FDT may be located anywhere in system RAM */
+static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base)
+{
+	return ULONG_MAX;
+}
+
+/*
+ * On arm64, we have to ensure that the initrd ends up in the linear region,
+ * which is a 1 GB aligned region of size '1UL << (VA_BITS - 1)' that is
+ * guaranteed to cover the kernel Image.
+ *
+ * Since the EFI stub is part of the kernel Image, we can relax the
+ * usual requirements in Documentation/arm64/booting.txt, which still
+ * apply to other bootloaders, and are required for some kernel
+ * configurations.
+ */
+static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
+						    unsigned long image_addr)
+{
+	return (image_addr & ~(SZ_1G - 1UL)) + (1UL << (VA_BITS - 1));
+}
 
 #define efi_call_early(f, ...)		sys_table_arg->boottime->f(__VA_ARGS__)
 #define __efi_call_early(f, ...)	f(__VA_ARGS__)

drivers/firmware/efi/libstub/arm-stub.c

@@ -213,8 +213,9 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
 	if (!fdt_addr)
 		pr_efi(sys_table, "Generating empty DTB\n");
 
-	status = handle_cmdline_files(sys_table, image, cmdline_ptr,
-				      "initrd=", dram_base + SZ_512M,
+	status = handle_cmdline_files(sys_table, image, cmdline_ptr, "initrd=",
+				      efi_get_max_initrd_addr(dram_base,
+							      *image_addr),
 				      (unsigned long *)&initrd_addr,
 				      (unsigned long *)&initrd_size);
 	if (status != EFI_SUCCESS)
@@ -224,7 +225,7 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
 
 	new_fdt_addr = fdt_addr;
 	status = allocate_new_fdt_and_exit_boot(sys_table, handle,
-				&new_fdt_addr, dram_base + MAX_FDT_OFFSET,
+				&new_fdt_addr, efi_get_max_fdt_addr(dram_base),
 				initrd_addr, initrd_size, cmdline_ptr,
 				fdt_addr, fdt_size);