From f7b78ba1e5e0e82cfb49f0e774cde210823179d4 Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Tue, 30 Jun 2020 16:32:59 +0100 Subject: [PATCH] [PATCH] [efi] Raise TPL during driver entry point As per commit c89a446 ("[efi] Run at TPL_CALLBACK to protect against UEFI timers") we expect to run at TPL_CALLBACK almost all of the time. Various code paths rely on this assumption. Code paths that need to temporarily lower the TPL (e.g. for entropy gathering) will restore it to TPL_CALLBACK. The entropy gathering code will be run during DRBG initialisation, which happens during the call to startup(). In the case of iPXE compiled as an EFI application this code will run within the scope of efi_snp_claim() and so will execute at TPL_CALLBACK as expected. In the case of iPXE compiled as an EFI driver the code will incorrectly run at TPL_APPLICATION since there is nothing within the EFI driver entry point that raises (and restores) the TPL. The net effect is that a build that includes the entropy-gathering code (e.g. a build with HTTPS enabled) will return from the driver entry point at TPL_CALLBACK, which causes a system lockup. Fix by raising and restoring the TPL within the EFI driver entry point. Debugged-by: Ignat Korchagin Signed-off-by: Michael Brown Origin: backport, https://github.com/ipxe/ipxe/commit/2ae5d4338661b65c63eb5cb1a96e5b803fe7d620 Bug-Ubuntu: https://bugs.launchpad.net/bugs/1882671 Last-Update: 2020-07-16 Gbp-Pq: Name lp-1882671-efi-Raise-TPL-during-driver-entry-point.patch --- src/interface/efi/efidrvprefix.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/src/interface/efi/efidrvprefix.c b/src/interface/efi/efidrvprefix.c index 4fbb19f..a8ef667 100644 --- a/src/interface/efi/efidrvprefix.c +++ b/src/interface/efi/efidrvprefix.c @@ -34,16 +34,25 @@ FILE_LICENCE ( GPL2_OR_LATER ); */ EFI_STATUS EFIAPI _efidrv_start ( EFI_HANDLE image_handle, EFI_SYSTEM_TABLE *systab ) { + EFI_BOOT_SERVICES *bs; + EFI_TPL saved_tpl; EFI_STATUS efirc; /* Initialise EFI environment */ if ( ( efirc = efi_init ( image_handle, systab ) ) != 0 ) return efirc; + /* Raise TPL */ + bs = efi_systab->BootServices; + saved_tpl = bs->RaiseTPL ( TPL_CALLBACK ); + /* Initialise iPXE environment */ initialise(); startup(); + /* Restore TPL */ + bs->RestoreTPL ( saved_tpl ); + return 0; }