| From 1a3887924a7e6edd331be76da7bf4c1e8eab4b1e Mon Sep 17 00:00:00 2001 |
| From: Ard Biesheuvel <ardb@kernel.org> |
| Date: Mon, 22 Aug 2022 19:20:33 +0200 |
| Subject: efi: libstub: Disable struct randomization |
| |
| From: Ard Biesheuvel <ardb@kernel.org> |
| |
| commit 1a3887924a7e6edd331be76da7bf4c1e8eab4b1e upstream. |
| |
| The EFI stub is a wrapper around the core kernel that makes it look like |
| a EFI compatible PE/COFF application to the EFI firmware. EFI |
| applications run on top of the EFI runtime, which is heavily based on |
| so-called protocols, which are struct types consisting [mostly] of |
| function pointer members that are instantiated and recorded in a |
| protocol database. |
| |
| These structs look like the ideal randomization candidates to the |
| randstruct plugin (as they only carry function pointers), but of course, |
| these protocols are contracts between the firmware that exposes them, |
| and the EFI applications (including our stubbed kernel) that invoke |
| them. This means that struct randomization for EFI protocols is not a |
| great idea, and given that the stub shares very little data with the |
| core kernel that is represented as a randomizable struct, we're better |
| off just disabling it completely here. |
| |
| Cc: <stable@vger.kernel.org> # v4.14+ |
| Reported-by: Daniel Marth <daniel.marth@inso.tuwien.ac.at> |
| Tested-by: Daniel Marth <daniel.marth@inso.tuwien.ac.at> |
| Signed-off-by: Ard Biesheuvel <ardb@kernel.org> |
| Acked-by: Kees Cook <keescook@chromium.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| drivers/firmware/efi/libstub/Makefile | 7 +++++++ |
| 1 file changed, 7 insertions(+) |
| |
| --- a/drivers/firmware/efi/libstub/Makefile |
| +++ b/drivers/firmware/efi/libstub/Makefile |
| @@ -37,6 +37,13 @@ KBUILD_CFLAGS := $(cflags-y) -Os -DDIS |
| $(call cc-option,-fno-addrsig) \ |
| -D__DISABLE_EXPORTS |
| |
| +# |
| +# struct randomization only makes sense for Linux internal types, which the EFI |
| +# stub code never touches, so let's turn off struct randomization for the stub |
| +# altogether |
| +# |
| +KBUILD_CFLAGS := $(filter-out $(RANDSTRUCT_CFLAGS), $(KBUILD_CFLAGS)) |
| + |
| # remove SCS flags from all objects in this directory |
| KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS)) |
| # disable LTO |
