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In-Reply-To: <9f951d6332eea6e46ebd46ca919ed5b1b85c0ba3.1671098103.git.baskov@ispras.ru>
From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Fri, 10 Mar 2023 15:56:20 +0100
Message-ID: <CAMj1kXGwaX8nGJdRM3==thO=KfXb3UwbF2jJhrqiZK-RcM+QLw@mail.gmail.com>
Subject: Re: [PATCH v4 13/26] x86/boot: Split trampoline and pt init code
To:     Evgeniy Baskov <baskov@ispras.ru>
Cc:     Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alexey Khoroshilov <khoroshilov@ispras.ru>,
        Peter Jones <pjones@redhat.com>,
        "Limonciello, Mario" <mario.limonciello@amd.com>,
        joeyli <jlee@suse.com>, lvc-project@linuxtesting.org,
        x86@kernel.org, linux-efi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@ispras.ru> wrote:
>
> When allocating trampoline from libstub trampoline allocation is
> performed separately, so it needs to be skipped.
>
> Split trampoline initialization and allocation code into two
> functions to make them invokable separately.
>
> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
> Tested-by: Peter Jones <pjones@redhat.com>
> Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>
> ---
>  arch/x86/boot/compressed/pgtable_64.c | 73 +++++++++++++++++----------
>  1 file changed, 46 insertions(+), 27 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
> index c7cf5a1059a8..1f7169248612 100644
> --- a/arch/x86/boot/compressed/pgtable_64.c
> +++ b/arch/x86/boot/compressed/pgtable_64.c
> @@ -106,12 +106,8 @@ static unsigned long find_trampoline_placement(void)
>         return bios_start - TRAMPOLINE_32BIT_SIZE;
>  }
>
> -struct paging_config paging_prepare(void *rmode)
> +bool trampoline_pgtable_init(struct boot_params *boot_params)
>  {
> -       struct paging_config paging_config = {};
> -
> -       /* Initialize boot_params. Required for cmdline_find_option_bool(). */
> -       boot_params = rmode;
>
>         /*
>          * Check if LA57 is desired and supported.
> @@ -125,26 +121,10 @@ struct paging_config paging_prepare(void *rmode)
>          *
>          * That's substitute for boot_cpu_has() in early boot code.
>          */
> -       if (IS_ENABLED(CONFIG_X86_5LEVEL) &&
> -                       !cmdline_find_option_bool("no5lvl") &&
> -                       native_cpuid_eax(0) >= 7 &&
> -                       (native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)))) {
> -               paging_config.l5_required = 1;
> -       }
> -
> -       paging_config.trampoline_start = find_trampoline_placement();
> -
> -       trampoline_32bit = (unsigned long *)paging_config.trampoline_start;
> -
> -       /* Preserve trampoline memory */
> -       memcpy(trampoline_save, trampoline_32bit, TRAMPOLINE_32BIT_SIZE);
> -
> -       /* Clear trampoline memory first */
> -       memset(trampoline_32bit, 0, TRAMPOLINE_32BIT_SIZE);
> -
> -       /* Copy trampoline code in place */
> -       memcpy(trampoline_32bit + TRAMPOLINE_32BIT_CODE_OFFSET / sizeof(unsigned long),
> -                       &trampoline_32bit_src, TRAMPOLINE_32BIT_CODE_SIZE);
> +       bool l5_required = IS_ENABLED(CONFIG_X86_5LEVEL) &&
> +                          !cmdline_find_option_bool("no5lvl") &&
> +                          native_cpuid_eax(0) >= 7 &&
> +                          (native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)));
>
>         /*
>          * The code below prepares page table in trampoline memory.
> @@ -160,10 +140,10 @@ struct paging_config paging_prepare(void *rmode)
>          * We are not going to use the page table in trampoline memory if we
>          * are already in the desired paging mode.
>          */
> -       if (paging_config.l5_required == !!(native_read_cr4() & X86_CR4_LA57))
> +       if (l5_required == !!(native_read_cr4() & X86_CR4_LA57))
>                 goto out;
>
> -       if (paging_config.l5_required) {
> +       if (l5_required) {
>                 /*
>                  * For 4- to 5-level paging transition, set up current CR3 as
>                  * the first and the only entry in a new top-level page table.
> @@ -185,6 +165,45 @@ struct paging_config paging_prepare(void *rmode)
>                        (void *)src, PAGE_SIZE);
>         }
>
> +out:
> +       return l5_required;
> +}
> +
> +struct paging_config paging_prepare(void *rmode)
> +{
> +       struct paging_config paging_config = {};
> +       bool early_trampoline_alloc = 0;

false

> +
> +       /* Initialize boot_params. Required for cmdline_find_option_bool(). */
> +       boot_params = rmode;
> +
> +       /*
> +        * We only need to find trampoline placement, if we have
> +        * not already done it from libstub.
> +        */
> +
> +       paging_config.trampoline_start = find_trampoline_placement();
> +       trampoline_32bit = (unsigned long *)paging_config.trampoline_start;
> +       early_trampoline_alloc = 0;
> +

false again

And it never becomes true, nor is it used anywhere else. Can we get rid of it?

> +       /*
> +        * Preserve trampoline memory.
> +        * When trampoline is located in memory
> +        * owned by us, i.e. allocated in EFISTUB,
> +        * we don't care about previous contents
> +        * of this memory so copying can also be skipped.

Can you please reflow comments so they takes up fewer lines?

> +        */
> +       memcpy(trampoline_save, trampoline_32bit, TRAMPOLINE_32BIT_SIZE);
> +
> +       /* Clear trampoline memory first */
> +       memset(trampoline_32bit, 0, TRAMPOLINE_32BIT_SIZE);
> +
> +       /* Copy trampoline code in place */
> +       memcpy(trampoline_32bit + TRAMPOLINE_32BIT_CODE_OFFSET / sizeof(unsigned long),
> +                       &trampoline_32bit_src, TRAMPOLINE_32BIT_CODE_SIZE);
> +
> +       paging_config.l5_required = trampoline_pgtable_init(boot_params);
> +
>  out:
>         return paging_config;
>  }
> --
> 2.37.4
>