linux-kernel - Re: [PATCH] KVM: arm64: Don't use cbz/adr with external symbols

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Message-ID: <202103051222.1E08D7D31@keescook>
Date:   Fri, 5 Mar 2021 12:22:36 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Ard Biesheuvel <ardb@...nel.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: Don't use cbz/adr with external symbols

On Fri, Mar 05, 2021 at 12:21:24PM -0800, Sami Tolvanen 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):
>   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
> 
> This is because with LTO, the compiler ends up placing hyp_panic()
> more than 1MB away from __guest_enter(). Use an unconditional branch
> and adr_l instead to fix the issue.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1317
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Suggested-by: Marc Zyngier <maz@...nel.org>
> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook