On 26 February 2016 at 16:01, Matt Fleming [off-list ref] wrote:

On Fri, 26 Feb, at 03:20:35PM, Ard Biesheuvel wrote:

quoted

Commit 2eec5dedf770 ("efi/arm-init: Use read-only early mappings")
updated the early ARM UEFI init code to create the temporary, early
mapping of the UEFI System table using read-only attributes, as a
hardening measure against inadvertent modification.

However, this still leaves the permanent, writable mapping of the UEFI
System table, which is only ever referenced during invocations of UEFI
Runtime Services, at which time the UEFI virtual mapping is available,
which also covers the system table. (This is guaranteed by the fact that
SetVirtualAddressMap(), which is a runtime service itself, converts
various entries in the table to their virtual equivalents, which implies
that the table must be covered by a RuntimeServicesData region that has
the EFI_MEMORY_RUNTIME attribute.)

So instead of creating this permanent mapping, record the virtual address
of the system table inside the UEFI virtual mapping, and dereference that
when accessing the table. This protects the contents of the system table
from inadvertent (or deliberate) modification when no UEFI Runtime
Services calls are in progress.

Signed-off-by: Ard Biesheuvel <redacted>
---
 drivers/firmware/efi/arm-init.c    |  2 ++
 drivers/firmware/efi/arm-runtime.c | 27 ++++++++++++++++-----------
 2 files changed, 18 insertions(+), 11 deletions(-)

Looks like a nice cleanup. Applied.

This patch causes a warning I hadn't spotted before sending it out.
Could you fold this in please?

diff --git a/drivers/firmware/efi/arm-runtime.c

b/drivers/firmware/efi/arm-runtime.c
index 6c97d4884fc7..fe749da9997e 100644

--- a/drivers/firmware/efi/arm-runtime.c
+++ b/drivers/firmware/efi/arm-runtime.c

@@ -72,8 +72,8 @@ static bool __init efi_virtmap_init(void)
                 */
                if (efi_system_table >= phys &&
                    efi_system_table < phys + (md->num_pages * EFI_PAGE_SIZE)) {
-                       efi.systab = (void *)(efi_system_table - phys +
-                                             md->virt_addr);
+                       efi.systab = (void *)(unsigned long)(efi_system_table -
+                                                         phys + md->virt_addr);
                        systab_found = true;
                }
        }

Thanks,
Ard.