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Date: Sat, 11 Mar 2023 17:37:45 +0300
From: Evgeniy Baskov <baskov@...ras.ru>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Alexey Khoroshilov <khoroshilov@...ras.ru>,
Peter Jones <pjones@...hat.com>,
"Limonciello, Mario" <mario.limonciello@....com>,
joeyli <jlee@...e.com>, lvc-project@...uxtesting.org,
x86@...nel.org, linux-efi@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 13/26] x86/boot: Split trampoline and pt init code
On 2023-03-10 17:56, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@...ras.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@....com>
>> Tested-by: Peter Jones <pjones@...hat.com>
>> Signed-off-by: Evgeniy Baskov <baskov@...ras.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?
Yes, probably it is just a leftover of the approach I used
before. I'll remove that.
>
>> + /*
>> + * 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?
>
Will fix.
>> + */
>> + 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
>>
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