linux-kernel - Re: [PATCH] KVM: arm64: Disable LTO in hyp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87k0qmzq5u.wl-maz@kernel.org>
Date:   Thu, 04 Mar 2021 19:15:25 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     James Morse <james.morse@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Disable LTO in hyp

On Thu, 04 Mar 2021 18:45:44 +0000,
Sami Tolvanen <samitolvanen@...gle.com> wrote:
> 
> allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following
> linker errors:
> 
>   ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC):

I assume this message is only an oddity, right? Because
__guest_enter() is as far as you can imagine from irqbypass.c...

>   relocation R_AARCH64_CONDBR19 out of range: 2031220 is not in
>   [-1048576, 1048575]; references hyp_panic
>   >>> defined in vmlinux.o
> 
>   ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21E0):
>   relocation R_AARCH64_ADR_PREL_LO21 out of range: 2031200 is not in
>   [-1048576, 1048575]; references hyp_panic
>   >>> defined in vmlinux.o
> 
> As LTO is not really necessary for the hypervisor code, disable it for
> the hyp directory to fix the build.

Can you shed some light on what the problem is exactly?

> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1317
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Tested-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
>  arch/arm64/kvm/hyp/Makefile | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
> index 687598e41b21..e8116016e6a8 100644
> --- a/arch/arm64/kvm/hyp/Makefile
> +++ b/arch/arm64/kvm/hyp/Makefile
> @@ -11,3 +11,6 @@ subdir-ccflags-y := -I$(incdir)				\
>  		    $(DISABLE_STACKLEAK_PLUGIN)
>  
>  obj-$(CONFIG_KVM) += vhe/ nvhe/ pgtable.o
> +
> +# Disable LTO for the files in this directory
> +KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))
> 
> base-commit: f69d02e37a85645aa90d18cacfff36dba370f797

Can this be reduced to the nvhe part of the tree? The rest of the
hypervisor should support being built with LTO, I'd expect. Or am I
missing something more significant?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.