Michael Brown
259 lines
7.0 KiB
C
259 lines
7.0 KiB
C
/*
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* Copyright (C) 2022 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*
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* You can also choose to distribute this program under the terms of
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* the Unmodified Binary Distribution Licence (as given in the file
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* COPYING.UBDL), provided that you have satisfied its requirements.
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*/
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FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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#include <string.h>
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#include <stdlib.h>
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#include <errno.h>
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#include <ipxe/image.h>
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#include <ipxe/efi/efi.h>
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#include <ipxe/efi/efi_strings.h>
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#include <ipxe/efi/efi_shim.h>
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#include <ipxe/efi/Protocol/PxeBaseCode.h>
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#include <ipxe/efi/Protocol/ShimLock.h>
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/** @file
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*
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* UEFI shim special handling
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*
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*/
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FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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/**
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* Require use of a third party loader binary
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*
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* The UEFI shim is gradually becoming less capable of directly
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* executing a Linux kernel image, due to an ever increasing list of
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* assumptions that it will only ever be used in conjunction with a
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* second stage loader binary such as GRUB.
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*
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* For example: shim will erroneously complain if the image that it
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* loads and executes does not in turn call in to the "shim lock
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* protocol" to verify a separate newly loaded binary before calling
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* ExitBootServices(), even if no such separate binary is used or
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* required.
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*
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* Experience shows that there is unfortunately no point in trying to
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* get a fix for this upstreamed into shim. We therefore default to
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* reducing the Secure Boot attack surface by removing, where
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* possible, this spurious requirement for the use of an additional
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* second stage loader.
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*
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* This option may be used to require the use of an additional second
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* stage loader binary, in case this behaviour is ever desirable.
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*/
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int efi_shim_require_loader = 0;
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/**
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* Allow use of PXE base code protocol
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*
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* We provide shim with access to all of the relevant downloaded files
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* via our EFI_SIMPLE_FILE_SYSTEM_PROTOCOL interface. However, shim
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* will instead try to redownload the files via TFTP since it prefers
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* to use the EFI_PXE_BASE_CODE_PROTOCOL installed on the same handle.
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*
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* Experience shows that there is unfortunately no point in trying to
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* get a fix for this upstreamed into shim. We therefore default to
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* working around this undesirable behaviour by stopping the PXE base
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* code protocol before invoking shim.
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*
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* This option may be used to allow shim to use the PXE base code
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* protocol, in case this behaviour is ever desirable.
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*/
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int efi_shim_allow_pxe = 0;
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/** UEFI shim image */
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struct image_tag efi_shim __image_tag = {
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.name = "SHIM",
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};
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/** Original GetMemoryMap() function */
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static EFI_GET_MEMORY_MAP efi_shim_orig_get_memory_map;
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/**
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* Unlock UEFI shim
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*
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*/
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static void efi_shim_unlock ( void ) {
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EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
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uint8_t empty[0];
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union {
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EFI_SHIM_LOCK_PROTOCOL *lock;
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void *interface;
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} u;
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EFI_STATUS efirc;
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/* Locate shim lock protocol */
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if ( ( efirc = bs->LocateProtocol ( &efi_shim_lock_protocol_guid,
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NULL, &u.interface ) ) == 0 ) {
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u.lock->Verify ( empty, sizeof ( empty ) );
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DBGC ( &efi_shim, "SHIM unlocked via %p\n", u.lock );
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}
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}
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/**
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* Wrap GetMemoryMap()
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*
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* @v len Memory map size
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* @v map Memory map
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* @v key Memory map key
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* @v desclen Descriptor size
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* @v descver Descriptor version
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* @ret efirc EFI status code
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*/
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static EFIAPI EFI_STATUS efi_shim_get_memory_map ( UINTN *len,
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EFI_MEMORY_DESCRIPTOR *map,
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UINTN *key, UINTN *desclen,
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UINT32 *descver ) {
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/* Unlock shim */
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if ( ! efi_shim_require_loader )
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efi_shim_unlock();
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/* Hand off to original GetMemoryMap() */
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return efi_shim_orig_get_memory_map ( len, map, key, desclen,
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descver );
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}
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/**
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* Inhibit use of PXE base code
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*
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* @v handle EFI handle
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* @ret rc Return status code
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*/
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static int efi_shim_inhibit_pxe ( EFI_HANDLE handle ) {
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EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
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union {
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EFI_PXE_BASE_CODE_PROTOCOL *pxe;
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void *interface;
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} u;
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EFI_STATUS efirc;
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int rc;
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/* Locate PXE base code */
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if ( ( efirc = bs->OpenProtocol ( handle,
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&efi_pxe_base_code_protocol_guid,
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&u.interface, efi_image_handle, NULL,
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EFI_OPEN_PROTOCOL_GET_PROTOCOL ))!=0){
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rc = -EEFI ( efirc );
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DBGC ( &efi_shim, "SHIM could not open PXE base code: %s\n",
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strerror ( rc ) );
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goto err_no_base;
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}
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/* Stop PXE base code */
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if ( ( efirc = u.pxe->Stop ( u.pxe ) ) != 0 ) {
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rc = -EEFI ( efirc );
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DBGC ( &efi_shim, "SHIM could not stop PXE base code: %s\n",
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strerror ( rc ) );
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goto err_stop;
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}
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/* Success */
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rc = 0;
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DBGC ( &efi_shim, "SHIM stopped PXE base code\n" );
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err_stop:
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bs->CloseProtocol ( handle, &efi_pxe_base_code_protocol_guid,
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efi_image_handle, NULL );
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err_no_base:
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return rc;
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}
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/**
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* Update command line
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*
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* @v shim Shim image
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* @v cmdline Command line to update
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* @ret rc Return status code
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*/
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static int efi_shim_cmdline ( struct image *shim, wchar_t **cmdline ) {
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wchar_t *shimcmdline;
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int len;
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int rc;
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/* Construct new command line */
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len = ( shim->cmdline ?
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efi_asprintf ( &shimcmdline, "%s %s", shim->name,
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shim->cmdline ) :
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efi_asprintf ( &shimcmdline, "%s %ls", shim->name,
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*cmdline ) );
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if ( len < 0 ) {
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rc = len;
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DBGC ( &efi_shim, "SHIM could not construct command line: "
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"%s\n", strerror ( rc ) );
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return rc;
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}
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/* Replace command line */
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free ( *cmdline );
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*cmdline = shimcmdline;
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return 0;
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}
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/**
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* Install UEFI shim special handling
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*
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* @v shim Shim image
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* @v handle EFI device handle
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* @v cmdline Command line to update
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* @ret rc Return status code
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*/
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int efi_shim_install ( struct image *shim, EFI_HANDLE handle,
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wchar_t **cmdline ) {
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EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
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int rc;
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/* Stop PXE base code */
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if ( ( ! efi_shim_allow_pxe ) &&
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( ( rc = efi_shim_inhibit_pxe ( handle ) ) != 0 ) ) {
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return rc;
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}
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/* Update command line */
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if ( ( rc = efi_shim_cmdline ( shim, cmdline ) ) != 0 )
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return rc;
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/* Record original boot services functions */
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efi_shim_orig_get_memory_map = bs->GetMemoryMap;
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/* Wrap relevant boot services functions */
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bs->GetMemoryMap = efi_shim_get_memory_map;
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return 0;
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}
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/**
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* Uninstall UEFI shim special handling
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*
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*/
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void efi_shim_uninstall ( void ) {
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EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
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/* Restore original boot services functions */
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bs->GetMemoryMap = efi_shim_orig_get_memory_map;
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}
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