linux-kernel - Re: [PATCH 4.14 06/40] efi: libstub: Disable struct randomization

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Message-ID: <20220926110826.GE8978@amd>
Date:   Mon, 26 Sep 2022 13:08:26 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Daniel Marth <daniel.marth@...o.tuwien.ac.at>,
        Ard Biesheuvel <ardb@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.14 06/40] efi: libstub: Disable struct randomization

Hi!

> 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@...r.kernel.org> # v4.14+

AFAICT RANDSTRUCT_CFLAGS is not available in v4.19, so we should not
take this patch.

Best regards,
								Pavel

> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -23,6 +23,13 @@ KBUILD_CFLAGS			:= $(cflags-y) -DDISABLE_BRANCH_PROFILING \
>  				   $(call cc-option,-ffreestanding) \
>  				   $(call cc-option,-fno-stack-protector)
>  
> +#
> +# 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))
>  

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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