From mboxrd@z Thu Jan 1 00:00:00 1970 From: ard.biesheuvel@linaro.org (Ard Biesheuvel) Date: Mon, 12 Sep 2016 17:15:25 +0100 Subject: [PATCH v3] arm64: mm: move zero page from .bss to right before swapper_pg_dir Message-ID: <1473696925-26156-1-git-send-email-ard.biesheuvel@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Move the statically allocated zero page from the .bss section to right before swapper_pg_dir. This allows us to refer to its physical address by simply reading TTBR1_EL1 (which always points to swapper_pg_dir and always has its ASID field cleared), and subtracting PAGE_SIZE. To protect the zero page from inadvertent modification, carve out a segment that covers it as well as idmap_pg_dir[], and mark it read-only in both the primary and the linear mappings of the kernel. Signed-off-by: Ard Biesheuvel --- v3: rebase onto for-next/core add clarifying comments around cpu_set_reserved_ttbr0() reduce alignment of r/o region covering idmap_pg_dir and empty_zero_page to PAGE_SIZE rename vmlinux_tail vm_struct to vmlinux_swapper v2: make empty_zero_page[] read-only make idmap_pg_dir[] read-only as well fix issue in v1 with cpu_reserved_ttbr0() arch/arm64/include/asm/mmu_context.h | 18 +++++-- arch/arm64/include/asm/sections.h | 1 + arch/arm64/kernel/vmlinux.lds.S | 9 ++++ arch/arm64/mm/mmu.c | 56 ++++++++++++-------- 4 files changed, 57 insertions(+), 27 deletions(-) diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h index a50185375f09..c934449504a2 100644 --- a/arch/arm64/include/asm/mmu_context.h +++ b/arch/arm64/include/asm/mmu_context.h @@ -41,12 +41,16 @@ static inline void contextidr_thread_switch(struct task_struct *next) /* * Set TTBR0 to empty_zero_page. No translations will be possible via TTBR0. + * In some cases (e.g. where cpu_replace_ttbr1 is used), TTBR1 may not + * point at swapper_pg_dir, and this helper cannot be used. */ static inline void cpu_set_reserved_ttbr0(void) { - unsigned long ttbr = virt_to_phys(empty_zero_page); - - write_sysreg(ttbr, ttbr0_el1); + /* + * The zero page is located right before swapper_pg_dir, whose + * physical address we can easily fetch from TTBR1_EL1. + */ + write_sysreg(read_sysreg(ttbr1_el1) - PAGE_SIZE, ttbr0_el1); isb(); } @@ -99,7 +103,9 @@ static inline void cpu_uninstall_idmap(void) { struct mm_struct *mm = current->active_mm; - cpu_set_reserved_ttbr0(); + /* see cpu_set_reserved_ttbr0 */ + write_sysreg(virt_to_phys(empty_zero_page), ttbr0_el1); + isb(); local_flush_tlb_all(); cpu_set_default_tcr_t0sz(); @@ -109,7 +115,9 @@ static inline void cpu_uninstall_idmap(void) static inline void cpu_install_idmap(void) { - cpu_set_reserved_ttbr0(); + /* see cpu_set_reserved_ttbr0 */ + write_sysreg(virt_to_phys(empty_zero_page), ttbr0_el1); + isb(); local_flush_tlb_all(); cpu_set_idmap_tcr_t0sz(); diff --git a/arch/arm64/include/asm/sections.h b/arch/arm64/include/asm/sections.h index 4e7e7067afdb..44e94e234ba0 100644 --- a/arch/arm64/include/asm/sections.h +++ b/arch/arm64/include/asm/sections.h @@ -26,5 +26,6 @@ extern char __hyp_text_start[], __hyp_text_end[]; extern char __idmap_text_start[], __idmap_text_end[]; extern char __irqentry_text_start[], __irqentry_text_end[]; extern char __mmuoff_data_start[], __mmuoff_data_end[]; +extern char __robss_start[], __robss_end[]; #endif /* __ASM_SECTIONS_H */ diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 5ce9b2929e0d..0f0675645f47 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -210,8 +210,17 @@ SECTIONS BSS_SECTION(0, 0, 0) . = ALIGN(PAGE_SIZE); + __robss_start = .; idmap_pg_dir = .; . += IDMAP_DIR_SIZE; + /* + * Put the zero page right before swapper_pg_dir so we can + * easily obtain its physical address by subtracting PAGE_SIZE + * from the contents of TTBR1_EL1. + */ + empty_zero_page = .; + . += PAGE_SIZE; + __robss_end = .; swapper_pg_dir = .; . += SWAPPER_DIR_SIZE; diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 05615a3fdc6f..d2be62ff1ad3 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -52,7 +52,6 @@ EXPORT_SYMBOL(kimage_voffset); * Empty_zero_page is a special page that is used for zero-initialized data * and COW. */ -unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss; EXPORT_SYMBOL(empty_zero_page); static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss; @@ -319,16 +318,18 @@ static void create_mapping_late(phys_addr_t phys, unsigned long virt, static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end) { - unsigned long kernel_start = __pa(_text); - unsigned long kernel_end = __pa(__init_begin); + unsigned long text_start = __pa(_text); + unsigned long text_end = __pa(__init_begin); + unsigned long robss_start = __pa(__robss_start); + unsigned long robss_end = __pa(__robss_end); /* * Take care not to create a writable alias for the - * read-only text and rodata sections of the kernel image. + * read-only text/rodata/robss sections of the kernel image. */ - /* No overlap with the kernel text/rodata */ - if (end < kernel_start || start >= kernel_end) { + /* No overlap with the kernel text/rodata/robss */ + if (end < text_start || start >= robss_end) { __create_pgd_mapping(pgd, start, __phys_to_virt(start), end - start, PAGE_KERNEL, early_pgtable_alloc, @@ -340,27 +341,32 @@ static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end * This block overlaps the kernel text/rodata mappings. * Map the portion(s) which don't overlap. */ - if (start < kernel_start) - __create_pgd_mapping(pgd, start, - __phys_to_virt(start), - kernel_start - start, PAGE_KERNEL, + if (start < text_start) + __create_pgd_mapping(pgd, start, __phys_to_virt(start), + text_start - start, PAGE_KERNEL, early_pgtable_alloc, !debug_pagealloc_enabled()); - if (kernel_end < end) - __create_pgd_mapping(pgd, kernel_end, - __phys_to_virt(kernel_end), - end - kernel_end, PAGE_KERNEL, + if (robss_end < end) + __create_pgd_mapping(pgd, robss_end, __phys_to_virt(robss_end), + end - robss_end, PAGE_KERNEL, early_pgtable_alloc, !debug_pagealloc_enabled()); /* - * Map the linear alias of the [_text, __init_begin) interval as - * read-only/non-executable. This makes the contents of the - * region accessible to subsystems such as hibernate, but - * protects it from inadvertent modification or execution. + * Map the linear alias of the intervals [_text, __init_begin) and + * [robss_start, robss_end) as read-only/non-executable. This makes + * the contents of these regions accessible to subsystems such + * as hibernate, but protects them from inadvertent modification or + * execution. */ - __create_pgd_mapping(pgd, kernel_start, __phys_to_virt(kernel_start), - kernel_end - kernel_start, PAGE_KERNEL_RO, + __create_pgd_mapping(pgd, text_start, __phys_to_virt(text_start), + text_end - text_start, PAGE_KERNEL_RO, + early_pgtable_alloc, !debug_pagealloc_enabled()); + __create_pgd_mapping(pgd, text_end, __phys_to_virt(text_end), + robss_start - text_end, PAGE_KERNEL, + early_pgtable_alloc, !debug_pagealloc_enabled()); + __create_pgd_mapping(pgd, robss_start, __phys_to_virt(robss_start), + robss_end - robss_start, PAGE_KERNEL_RO, early_pgtable_alloc, !debug_pagealloc_enabled()); } @@ -424,13 +430,19 @@ static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end, */ static void __init map_kernel(pgd_t *pgd) { - static struct vm_struct vmlinux_text, vmlinux_rodata, vmlinux_init, vmlinux_data; + static struct vm_struct vmlinux_text, vmlinux_rodata, vmlinux_init, + vmlinux_data, vmlinux_robss, vmlinux_swapper; map_kernel_segment(pgd, _text, _etext, PAGE_KERNEL_EXEC, &vmlinux_text); map_kernel_segment(pgd, __start_rodata, __init_begin, PAGE_KERNEL, &vmlinux_rodata); map_kernel_segment(pgd, __init_begin, __init_end, PAGE_KERNEL_EXEC, &vmlinux_init); - map_kernel_segment(pgd, _data, _end, PAGE_KERNEL, &vmlinux_data); + map_kernel_segment(pgd, _data, __robss_start, PAGE_KERNEL, + &vmlinux_data); + map_kernel_segment(pgd, __robss_start, __robss_end, PAGE_KERNEL_RO, + &vmlinux_robss); + map_kernel_segment(pgd, __robss_end, _end, PAGE_KERNEL, + &vmlinux_swapper); if (!pgd_val(*pgd_offset_raw(pgd, FIXADDR_START))) { /* -- 2.7.4