iPXE seems to be almost alone in the UEFI world in attempting to shut
down cleanly, free resources, and leave hardware in a well-defined
reset state before handing over to the booted operating system.
The UEFI driver model does allow for graceful shutdown via
uninstallation of protocol interfaces. However, virtually no other
UEFI drivers do this, and the external code paths that react to
uninstallation are consequently poorly tested. This leads to a
proliferation of bugs found in UEFI implementations in the wild, as
described in commits such as 1295b4a ("[efi] Allow initialisation via
SNP interface even while claimed") or b6e2ea0 ("[efi] Veto the HP
XhciDxe Driver").
Try to avoid triggering such bugs by unconditionally skipping the
protocol interface uninstallation during UEFI boot services shutdown,
leaving the interfaces present but nullified and deliberately leaking
the containing memory.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
The UEFI specification allows uninstallation of a protocol interface
to fail. There is no sensible way for code to react to this, since
uninstallation is likely to be taking place on a code path that cannot
itself fail (e.g. a code path that is itself a failure path).
Where the protocol structure exists within a dynamically allocated
block of memory, this leads to possible use-after-free bugs. Work
around this unfortunate design choice by nullifying the protocol
(i.e. overwriting the method pointers with no-ops) and leaking the
memory containing the protocol structure.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Mac OS X uses non-standard EFI protocols to obtain the DHCP packets
from the UEFI firmware.
Originally-implemented-by: Michael Kuron <m.kuron@gmx.de>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Many UEFI NBPs expect to find an EFI_PXE_BASE_CODE_PROTOCOL installed
in addition to the EFI_SIMPLE_NETWORK_PROTOCOL. Most NBPs use the
EFI_PXE_BASE_CODE_PROTOCOL only to retrieve the cached DHCP packets.
This implementation has been tested with grub.efi, shim.efi,
syslinux.efi, and wdsmgfw.efi. Some methods (such as Discover() and
Arp()) are not used by any known NBP and so have not (yet) been
implemented.
Usage notes for the tested bootstraps are:
- grub.efi uses EFI_PXE_BASE_CODE_PROTOCOL only to retrieve the
cached DHCP packet, and uses no other methods.
- shim.efi uses EFI_PXE_BASE_CODE_PROTOCOL to retrieve the cached
DHCP packet and to retrieve the next NBP via the Mtftp() method.
If shim.efi was downloaded via HTTP (or other non-TFTP protocol)
then shim.efi will blindly call Mtftp() with an HTTP URI as the
filename: this allows the next NBP (e.g. grubx64.efi) to also be
transparently retrieved by HTTP.
shim.efi can also use the EFI_SIMPLE_FILE_SYSTEM_PROTOCOL to
retrieve files previously loaded by "imgfetch" or similar commands
in iPXE. The current implementation of shim.efi will use the
EFI_SIMPLE_FILE_SYSTEM_PROTOCOL only if it does not find an
EFI_PXE_BASE_CODE_PROTOCOL; this patch therefore prevents this
usage of our EFI_SIMPLE_FILE_SYSTEM_PROTOCOL. This logic could be
trivially reversed in shim.efi if needed.
- syslinux.efi uses EFI_PXE_BASE_CODE_PROTOCOL only to retrieve the
cached DHCP packet. Versions 6.03 and earlier have a bug which
may cause syslinux.efi to attach to the wrong NIC if there are
multiple NICs in the system (or if the UEFI firmware supports
IPv6).
- wdsmgfw.efi (ab)uses EFI_PXE_BASE_CODE_PROTOCOL to retrieve the
cached DHCP packets, and to send and retrieve UDP packets via the
UdpWrite() and UdpRead() methods. (This was presumably done in
order to minimise the amount of benefit obtainable by switching to
UEFI, by replicating all of the design mistakes present in the
original PXE specification.)
The EFI_DOWNGRADE_UX configuration option remains available for now,
until this implementation has received more widespread testing.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
