linux-kernel - Re: [PATCH] x86: efi: avoid BUILD_BUG_ON() for non-constant p4d

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Message-ID: <20210115183203.GA1991122@ubuntu-m3-large-x86>
Date:   Fri, 15 Jan 2021 11:32:03 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Arnd Bergmann <arnd@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>, linux-efi@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] x86: efi: avoid BUILD_BUG_ON() for non-constant p4d_index

On Fri, Jan 15, 2021 at 07:23:00PM +0100, Borislav Petkov wrote:
> On Thu, Jan 07, 2021 at 11:34:15PM +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> > 
> > When 5-level page tables are enabled, clang triggers a BUILD_BUG_ON():
> 
> I have CONFIG_X86_5LEVEL=y, CONFIG_EFI=y and am using Debian clang
> version 10.0.1-8+b1 but my .config builds just fine.
> 
> How do you trigger this?

I triggered it with CONFIG_UBSAN=y + CONFIG_UBSAN_UNSIGNED_OVERFLOW=y
(it can be exposed with an allyesconfig/allmodconfig on mainline
currently).

Cheers,
Nathan