efi/arm/libstub: Pack FDT after populating it

commit 72a58a63a164b4e9d2d914e65caeb551846883f1 upstream.

Commit:

  24d7c494ce46 ("efi/arm-stub: Round up FDT allocation to mapping size")

increased the allocation size for the FDT image created by the stub to a
fixed value of 2 MB, to simplify the former code that made several
attempts with increasing values for the size. This is reasonable
given that the allocation is of type EFI_LOADER_DATA, which is released
to the kernel unless it is explicitly memblock_reserve()d by the early
boot code.

However, this allocation size leaked into the 'size' field of the FDT
header metadata, and so the entire allocation remains occupied by the
device tree binary, even if most of it is not used to store device tree
information.

So call fdt_pack() to shrink the FDT data structure to its minimum size
after populating all the fields, so that the remaining memory is no
longer wasted.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: <stable@vger.kernel.org> # v4.12+
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Fixes: 24d7c494ce46 ("efi/arm-stub: Round up FDT allocation to mapping size")
Link: http://lkml.kernel.org/r/20181114175544.12860-4-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
index 8830fa601e45d9a1b1094419cd1ec66f41a25e49..0c0d2312f4a8ad27f6e852bc82d5f2b6c0124e64 100644 (file)
--- a/drivers/firmware/efi/libstub/fdt.c
+++ b/drivers/firmware/efi/libstub/fdt.c
@@ -158,6 +158,10 @@ static efi_status_t update_fdt(efi_system_table_t *sys_table, void *orig_fdt,
                        return efi_status;
                }
        }
+
+       /* shrink the FDT back to its minimum size */
+       fdt_pack(fdt);
+
        return EFI_SUCCESS;
 
 fdt_set_fail: