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Message-ID: <4bb7e962bb4745894f20f752c5e48382@ispras.ru>
Date: Thu, 20 Oct 2022 14:30:43 +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>,
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 05/16] x86/boot: Support 4KB pages for identity mapping
On 2022-10-19 10:11, Ard Biesheuvel wrote:
> On Tue, 6 Sept 2022 at 12:42, Evgeniy Baskov <baskov@...ras.ru> wrote:
>>
>> Current identity mapping code only supports 2M and 1G pages.
>> 4KB pages are desirable for better memory protection granularity
>> in compressed kernel code.
>>
>> Change identity mapping code to support 4KB pages and
>> memory remapping with different attributes.
>>
>> Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
>
> This looks reasonable to me but someone on team-x86 will need to review
> this.
>
> One nit below
Thanks!
>
>> ---
>> arch/x86/include/asm/init.h | 1 +
>> arch/x86/mm/ident_map.c | 186
>> +++++++++++++++++++++++++++++-------
>> 2 files changed, 155 insertions(+), 32 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h
>> index 5f1d3c421f68..a8277ee82c51 100644
>> --- a/arch/x86/include/asm/init.h
>> +++ b/arch/x86/include/asm/init.h
>> @@ -8,6 +8,7 @@ struct x86_mapping_info {
>> unsigned long page_flag; /* page flag for PMD or PUD
>> entry */
>> unsigned long offset; /* ident mapping offset */
>> bool direct_gbpages; /* PUD level 1GB page support
>> */
>> + bool allow_4kpages; /* Allow more granular
>> mappings with 4K pages */
>> unsigned long kernpg_flag; /* kernel pagetable flag
>> override */
>> };
>>
>> diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
>> index 968d7005f4a7..ad455d4ef595 100644
>> --- a/arch/x86/mm/ident_map.c
>> +++ b/arch/x86/mm/ident_map.c
>> @@ -2,26 +2,130 @@
>> /*
>> * Helper routines for building identity mapping page tables. This is
>> * included by both the compressed kernel and the regular kernel.
>> + *
>
> Drop this change
>
>> */
>>
>> -static void ident_pmd_init(struct x86_mapping_info *info, pmd_t
>> *pmd_page,
>> - unsigned long addr, unsigned long end)
>> +static void ident_pte_init(struct x86_mapping_info *info, pte_t
>> *pte_page,
>> + unsigned long addr, unsigned long end,
>> + unsigned long flags)
>> {
>> - addr &= PMD_MASK;
>> - for (; addr < end; addr += PMD_SIZE) {
>> + addr &= PAGE_MASK;
>> + for (; addr < end; addr += PAGE_SIZE) {
>> + pte_t *pte = pte_page + pte_index(addr);
>> +
>> + set_pte(pte, __pte((addr - info->offset) | flags));
>> + }
>> +}
>> +
>> +pte_t *ident_split_large_pmd(struct x86_mapping_info *info,
>> + pmd_t *pmdp, unsigned long page_addr)
>> +{
>> + unsigned long pmd_addr, page_flags;
>> + pte_t *pte;
>> +
>> + pte = (pte_t *)info->alloc_pgt_page(info->context);
>> + if (!pte)
>> + return NULL;
>> +
>> + pmd_addr = page_addr & PMD_MASK;
>> +
>> + /* Not a large page - clear PSE flag */
>> + page_flags = pmd_flags(*pmdp) & ~_PSE;
>> + ident_pte_init(info, pte, pmd_addr, pmd_addr + PMD_SIZE,
>> page_flags);
>> +
>> + return pte;
>> +}
>> +
>> +static int ident_pmd_init(struct x86_mapping_info *info, pmd_t
>> *pmd_page,
>> + unsigned long addr, unsigned long end,
>> + unsigned long flags)
>> +{
>> + unsigned long next;
>> + bool new_table = 0;
>> +
>> + for (; addr < end; addr = next) {
>> pmd_t *pmd = pmd_page + pmd_index(addr);
>> + pte_t *pte;
>>
>> - if (pmd_present(*pmd))
>> + next = (addr & PMD_MASK) + PMD_SIZE;
>> + if (next > end)
>> + next = end;
>> +
>> + /*
>> + * Use 2M pages if 4k pages are not allowed or
>> + * we are not mapping extra, i.e. address and size are
>> aligned.
>> + */
>> +
>> + if (!info->allow_4kpages ||
>> + (!(addr & ~PMD_MASK) && next == addr + PMD_SIZE))
>> {
>> +
>> + pmd_t pmdval;
>> +
>> + addr &= PMD_MASK;
>> + pmdval = __pmd((addr - info->offset) | flags |
>> _PSE);
>> + set_pmd(pmd, pmdval);
>> continue;
>> + }
>> +
>> + /*
>> + * If currently mapped page is large, we need to split
>> it.
>> + * The case when we can remap 2M page to 2M page
>> + * with different flags is already covered above.
>> + *
>> + * If there's nothing mapped to desired address,
>> + * we need to allocate new page table.
>> + */
>>
>> - set_pmd(pmd, __pmd((addr - info->offset) |
>> info->page_flag));
>> + if (pmd_large(*pmd)) {
>> + pte = ident_split_large_pmd(info, pmd, addr);
>> + new_table = 1;
>> + } else if (!pmd_present(*pmd)) {
>> + pte = (pte_t
>> *)info->alloc_pgt_page(info->context);
>> + new_table = 1;
>> + } else {
>> + pte = pte_offset_kernel(pmd, 0);
>> + new_table = 0;
>> + }
>> +
>> + if (!pte)
>> + return -ENOMEM;
>> +
>> + ident_pte_init(info, pte, addr, next, flags);
>> +
>> + if (new_table)
>> + set_pmd(pmd, __pmd(__pa(pte) |
>> info->kernpg_flag));
>> }
>> +
>> + return 0;
>> }
>>
>> +
>> +pmd_t *ident_split_large_pud(struct x86_mapping_info *info,
>> + pud_t *pudp, unsigned long page_addr)
>> +{
>> + unsigned long pud_addr, page_flags;
>> + pmd_t *pmd;
>> +
>> + pmd = (pmd_t *)info->alloc_pgt_page(info->context);
>> + if (!pmd)
>> + return NULL;
>> +
>> + pud_addr = page_addr & PUD_MASK;
>> +
>> + /* Not a large page - clear PSE flag */
>> + page_flags = pud_flags(*pudp) & ~_PSE;
>> + ident_pmd_init(info, pmd, pud_addr, pud_addr + PUD_SIZE,
>> page_flags);
>> +
>> + return pmd;
>> +}
>> +
>> +
>> static int ident_pud_init(struct x86_mapping_info *info, pud_t
>> *pud_page,
>> unsigned long addr, unsigned long end)
>> {
>> unsigned long next;
>> + bool new_table = 0;
>> + int result;
>>
>> for (; addr < end; addr = next) {
>> pud_t *pud = pud_page + pud_index(addr);
>> @@ -31,28 +135,39 @@ static int ident_pud_init(struct x86_mapping_info
>> *info, pud_t *pud_page,
>> if (next > end)
>> next = end;
>>
>> + /* Use 1G pages only if forced, even if they are
>> supported. */
>> if (info->direct_gbpages) {
>> pud_t pudval;
>> -
>> - if (pud_present(*pud))
>> - continue;
>> + unsigned long flags;
>>
>> addr &= PUD_MASK;
>> - pudval = __pud((addr - info->offset) |
>> info->page_flag);
>> + flags = info->page_flag | _PSE;
>> + pudval = __pud((addr - info->offset) | flags);
>> +
>> set_pud(pud, pudval);
>> continue;
>> }
>>
>> - if (pud_present(*pud)) {
>> + if (pud_large(*pud)) {
>> + pmd = ident_split_large_pud(info, pud, addr);
>> + new_table = 1;
>> + } else if (!pud_present(*pud)) {
>> + pmd = (pmd_t
>> *)info->alloc_pgt_page(info->context);
>> + new_table = 1;
>> + } else {
>> pmd = pmd_offset(pud, 0);
>> - ident_pmd_init(info, pmd, addr, next);
>> - continue;
>> + new_table = 0;
>> }
>> - pmd = (pmd_t *)info->alloc_pgt_page(info->context);
>> +
>> if (!pmd)
>> return -ENOMEM;
>> - ident_pmd_init(info, pmd, addr, next);
>> - set_pud(pud, __pud(__pa(pmd) | info->kernpg_flag));
>> +
>> + result = ident_pmd_init(info, pmd, addr, next,
>> info->page_flag);
>> + if (result)
>> + return result;
>> +
>> + if (new_table)
>> + set_pud(pud, __pud(__pa(pmd) |
>> info->kernpg_flag));
>> }
>>
>> return 0;
>> @@ -63,6 +178,7 @@ static int ident_p4d_init(struct x86_mapping_info
>> *info, p4d_t *p4d_page,
>> {
>> unsigned long next;
>> int result;
>> + bool new_table = 0;
>>
>> for (; addr < end; addr = next) {
>> p4d_t *p4d = p4d_page + p4d_index(addr);
>> @@ -72,15 +188,14 @@ static int ident_p4d_init(struct x86_mapping_info
>> *info, p4d_t *p4d_page,
>> if (next > end)
>> next = end;
>>
>> - if (p4d_present(*p4d)) {
>> + if (!p4d_present(*p4d)) {
>> + pud = (pud_t
>> *)info->alloc_pgt_page(info->context);
>> + new_table = 1;
>> + } else {
>> pud = pud_offset(p4d, 0);
>> - result = ident_pud_init(info, pud, addr,
>> next);
>> - if (result)
>> - return result;
>> -
>> - continue;
>> + new_table = 0;
>> }
>> - pud = (pud_t *)info->alloc_pgt_page(info->context);
>> +
>> if (!pud)
>> return -ENOMEM;
>>
>> @@ -88,19 +203,22 @@ static int ident_p4d_init(struct x86_mapping_info
>> *info, p4d_t *p4d_page,
>> if (result)
>> return result;
>>
>> - set_p4d(p4d, __p4d(__pa(pud) | info->kernpg_flag));
>> + if (new_table)
>> + set_p4d(p4d, __p4d(__pa(pud) |
>> info->kernpg_flag));
>> }
>>
>> return 0;
>> }
>>
>> -int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t
>> *pgd_page,
>> - unsigned long pstart, unsigned long
>> pend)
>> +int kernel_ident_mapping_init(struct x86_mapping_info *info,
>> + pgd_t *pgd_page, unsigned long pstart,
>> + unsigned long pend)
>> {
>> unsigned long addr = pstart + info->offset;
>> unsigned long end = pend + info->offset;
>> unsigned long next;
>> int result;
>> + bool new_table;
>>
>> /* Set the default pagetable flags if not supplied */
>> if (!info->kernpg_flag)
>> @@ -117,20 +235,24 @@ int kernel_ident_mapping_init(struct
>> x86_mapping_info *info, pgd_t *pgd_page,
>> if (next > end)
>> next = end;
>>
>> - if (pgd_present(*pgd)) {
>> + if (!pgd_present(*pgd)) {
>> + p4d = (p4d_t
>> *)info->alloc_pgt_page(info->context);
>> + new_table = 1;
>> + } else {
>> p4d = p4d_offset(pgd, 0);
>> - result = ident_p4d_init(info, p4d, addr,
>> next);
>> - if (result)
>> - return result;
>> - continue;
>> + new_table = 0;
>> }
>>
>> - p4d = (p4d_t *)info->alloc_pgt_page(info->context);
>> if (!p4d)
>> return -ENOMEM;
>> +
>> result = ident_p4d_init(info, p4d, addr, next);
>> if (result)
>> return result;
>> +
>> + if (!new_table)
>> + continue;
>> +
>> if (pgtable_l5_enabled()) {
>> set_pgd(pgd, __pgd(__pa(p4d) |
>> info->kernpg_flag));
>> } else {
>> --
>> 2.35.1
>>
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