linux-kernel - Re: [RFC UKL 02/10] x86/boot: Load the PT

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Message-Id: <cecf0a31-8473-47bc-9af6-8a809267c9e6@app.fastmail.com>
Date:   Tue, 04 Oct 2022 10:30:18 -0700
From:   "Andy Lutomirski" <luto@...nel.org>
To:     "Ali Raza" <aliraza@...edu>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Cc:     "Jonathan Corbet" <corbet@....net>, masahiroy@...nel.org,
        michal.lkml@...kovi.net,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Kees Cook" <keescook@...omium.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Al Viro" <viro@...iv.linux.org.uk>,
        "Arnd Bergmann" <arnd@...db.de>, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        "Steven Rostedt" <rostedt@...dmis.org>,
        "Ben Segall" <bsegall@...gle.com>, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        "Paolo Bonzini" <pbonzini@...hat.com>, jpoimboe@...nel.org,
        linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org,
        "the arch/x86 maintainers" <x86@...nel.org>, rjones@...hat.com,
        munsoner@...edu, tommyu@...edu, drepper@...hat.com,
        lwoodman@...hat.com, mboydmcse@...il.com, okrieg@...edu,
        rmancuso@...edu
Subject: Re: [RFC UKL 02/10] x86/boot: Load the PT_TLS segment for Unikernel configs

On Mon, Oct 3, 2022, at 3:21 PM, Ali Raza wrote:
> The kernel normally skips loading this segment as it is not inlcuded in
> standard builds. However, when linked with an application in the Unikernel
> configuration the segment will be present. Load PT_TLS when configured as a
> unikernel.
>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: Michal Marek <michal.lkml@...kovi.net>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Eric Biederman <ebiederm@...ssion.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Josh Poimboeuf <jpoimboe@...nel.org>
>
> Signed-off-by: Ali Raza <aliraza@...edu>
> ---
>  arch/x86/boot/compressed/misc.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index cf690d8712f4..0d07b5661c9c 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -310,6 +310,9 @@ static void parse_elf(void *output)
>  		phdr = &phdrs[i];
> 
>  		switch (phdr->p_type) {
> +#ifdef CONFIG_UNIKERNEL_LINUX
> +		case PT_TLS:
> +#endif

Can you explain why exactly a Linux boot image would have a TLS segment?  What does it do?

>  		case PT_LOAD:
>  #ifdef CONFIG_X86_64
>  			if ((phdr->p_align % 0x200000) != 0)
> -- 
> 2.21.3