Messages in this thread Patch in this message | | | Subject | [PATCH 2/3] x86/mm: introduce __PAGE_KERNEL_GLOBAL | From | Dave Hansen <> | Date | Thu, 15 Feb 2018 05:20:55 -0800 |
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From: Dave Hansen <dave.hansen@linux.intel.com>
Kernel mappings are historically _PAGE_GLOBAL. But, with PTI, we do not want them to be _PAGE_GLOBAL. We currently accomplish this by simply clearing _PAGE_GLOBAL from the suppotred mask which ensures it is cleansed from many of our PTE construction sites:
if (!static_cpu_has(X86_FEATURE_PTI)) __supported_pte_mask |= _PAGE_GLOBAL;
But, this also means that we now get *no* opportunity to use global pages with PTI, even for data which is shared such as the cpu_entry_area and entry/exit text.
This patch introduces a new mask: __PAGE_KERNEL_GLOBAL. This mask can be thought of as the default global bit value when creating kernel mappings. We make it _PAGE_GLOBAL when PTI=n, but 0 when PTI=y. This ensures that on PTI kernels, all of the __PAGE_KERNEL_* users will not get _PAGE_GLOBAL.
This also restores _PAGE_GLOBAL to __supported_pte_mask, allowing it to be set in the first place.
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Kees Cook <keescook@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Juergen Gross <jgross@suse.com> Cc: x86@kernel.org ---
b/arch/x86/include/asm/pgtable_types.h | 9 ++++++++- b/arch/x86/mm/init.c | 8 +------- b/arch/x86/mm/pageattr.c | 9 +++++---- 3 files changed, 14 insertions(+), 12 deletions(-)
diff -puN arch/x86/include/asm/pgtable_types.h~kpti-no-global-for-kernel-mappings arch/x86/include/asm/pgtable_types.h --- a/arch/x86/include/asm/pgtable_types.h~kpti-no-global-for-kernel-mappings 2018-02-13 15:17:56.144210060 -0800 +++ b/arch/x86/include/asm/pgtable_types.h 2018-02-13 15:17:56.152210060 -0800 @@ -180,8 +180,15 @@ enum page_cache_mode { #define PAGE_READONLY_EXEC __pgprot(_PAGE_PRESENT | _PAGE_USER | \ _PAGE_ACCESSED) +#ifdef CONFIG_PAGE_TABLE_ISOLATION +#define __PAGE_KERNEL_GLOBAL 0 +#else +#define __PAGE_KERNEL_GLOBAL _PAGE_GLOBAL +#endif + #define __PAGE_KERNEL_EXEC \ - (_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_GLOBAL) + (_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED | \ + __PAGE_KERNEL_GLOBAL) #define __PAGE_KERNEL (__PAGE_KERNEL_EXEC | _PAGE_NX) #define __PAGE_KERNEL_RO (__PAGE_KERNEL & ~_PAGE_RW) diff -puN arch/x86/mm/init.c~kpti-no-global-for-kernel-mappings arch/x86/mm/init.c --- a/arch/x86/mm/init.c~kpti-no-global-for-kernel-mappings 2018-02-13 15:17:56.146210060 -0800 +++ b/arch/x86/mm/init.c 2018-02-13 15:17:56.152210060 -0800 @@ -162,12 +162,6 @@ struct map_range { static int page_size_mask; -static void enable_global_pages(void) -{ - if (!static_cpu_has(X86_FEATURE_PTI)) - __supported_pte_mask |= _PAGE_GLOBAL; -} - static void __init probe_page_size_mask(void) { /* @@ -189,7 +183,7 @@ static void __init probe_page_size_mask( __supported_pte_mask &= ~_PAGE_GLOBAL; if (boot_cpu_has(X86_FEATURE_PGE)) { cr4_set_bits_and_update_boot(X86_CR4_PGE); - enable_global_pages(); + __supported_pte_mask |= _PAGE_GLOBAL; } /* Enable 1 GB linear kernel mappings if available: */ diff -puN arch/x86/mm/pageattr.c~kpti-no-global-for-kernel-mappings arch/x86/mm/pageattr.c --- a/arch/x86/mm/pageattr.c~kpti-no-global-for-kernel-mappings 2018-02-13 15:17:56.148210060 -0800 +++ b/arch/x86/mm/pageattr.c 2018-02-13 15:17:56.153210060 -0800 @@ -593,7 +593,8 @@ try_preserve_large_page(pte_t *kpte, uns * different bit positions in the two formats. */ req_prot = pgprot_4k_2_large(req_prot); - req_prot = pgprot_set_on_present(req_prot, _PAGE_GLOBAL | _PAGE_PSE); + req_prot = pgprot_set_on_present(req_prot, + __PAGE_KERNEL_GLOBAL | _PAGE_PSE); req_prot = canon_pgprot(req_prot); /* @@ -703,7 +704,7 @@ __split_large_page(struct cpa_data *cpa, return 1; } - ref_prot = pgprot_set_on_present(ref_prot, _PAGE_GLOBAL); + ref_prot = pgprot_set_on_present(ref_prot, __PAGE_KERNEL_GLOBAL); /* * Get the target pfn from the original entry: @@ -926,7 +927,7 @@ static void populate_pte(struct cpa_data pte = pte_offset_kernel(pmd, start); - pgprot = pgprot_set_on_present(pgprot, _PAGE_GLOBAL); + pgprot = pgprot_set_on_present(pgprot, __PAGE_KERNEL_GLOBAL); pgprot = canon_pgprot(pgprot); while (num_pages-- && start < end) { @@ -1219,7 +1220,7 @@ repeat: new_prot = static_protections(new_prot, address, pfn); - new_prot = pgprot_set_on_present(new_prot, _PAGE_GLOBAL); + new_prot = pgprot_set_on_present(new_prot, __PAGE_KERNEL_GLOBAL); /* * We need to keep the pfn from the existing PTE, _
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