Re: [RFC UKL 02/10] x86/boot: Load the PT_TLS segment for Unikernel configs

[Andy Lutomirski]

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@xxxxxxx>
> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Cc: Michal Marek <michal.lkml@xxxxxxxxxxx>
> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
> Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Ben Segall <bsegall@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
>
> Signed-off-by: Ali Raza <aliraza@xxxxxx>
> ---
>  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