linux-kernel - Re: [PATCH 2/4] kexec: add CONFING_KEXEC_PURGATORY_SKIP

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Message-ID: <Yt6JRBToqY5ts6OU@zx2c4.com>
Date:   Mon, 25 Jul 2022 14:15:00 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Albert Huang <huangjie.albert@...edance.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Michael Roth <michael.roth@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Joerg Roedel <jroedel@...e.de>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 2/4] kexec: add CONFING_KEXEC_PURGATORY_SKIP_SIG

Hi Albert,

On Mon, Jul 25, 2022 at 04:38:54PM +0800, Albert Huang wrote:
> +config KEXEC_PURGATORY_SKIP_SIG
> +	bool "skip kexec purgatory signature verification"
> +	depends on ARCH_HAS_KEXEC_PURGATORY
> +	help
> +	  this options makes the kexec purgatory do  not signature verification
> +	  which would get hundreds of milliseconds saved during kexec boot. If we can
> +	  confirm that the data of each segment loaded by kexec will not change we may
> +	  enable this option
> +

Some grammar nits here, but actually, wouldn't it be better to make this
depend on some other signature things instead? Like if the parent kernel
actually did a big signature computation, then maybe the purgatory step
is needed, but if it didn't bother, then maybe you can skip it. This
way, you don't need a compile-time option that might change some aspect
of signature verification people might otherwise be relying on.

Jason