From mboxrd@z Thu Jan 1 00:00:00 1970 From: lauraa@codeaurora.org (Laura Abbott) Date: Wed, 20 Aug 2014 18:20:39 -0700 Subject: [PATCHv3 7/7] arm64: add better page protections to arm64 In-Reply-To: <1408584039-12735-1-git-send-email-lauraa@codeaurora.org> References: <1408584039-12735-1-git-send-email-lauraa@codeaurora.org> Message-ID: <1408584039-12735-8-git-send-email-lauraa@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Add page protections for arm64 similar to those in arm. This is for security reasons to prevent certain classes of exploits. The current method: - Map all memory as either RWX or RW. We round to the nearest section to avoid creating page tables before everything is mapped - Once everything is mapped, if either end of the RWX section should not be X, we split the PMD and remap as necessary - When initmem is to be freed, we change the permissions back to RW (using stop machine if necessary to flush the TLB) - If CONFIG_DEBUG_RODATA is set, the read only sections are set read only. Signed-off-by: Laura Abbott --- arch/arm64/Kconfig | 8 + arch/arm64/Kconfig.debug | 23 +++ arch/arm64/include/asm/cacheflush.h | 3 + arch/arm64/kernel/vmlinux.lds.S | 17 ++ arch/arm64/mm/init.c | 1 + arch/arm64/mm/mm.h | 2 + arch/arm64/mm/mmu.c | 303 +++++++++++++++++++++++++++++++----- 7 files changed, 321 insertions(+), 36 deletions(-) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index fd4e81a..b718974 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -328,6 +328,14 @@ config FORCE_MAX_ZONEORDER default "14" if (ARM64_64K_PAGES && TRANSPARENT_HUGEPAGE) default "11" +config NX_KERNEL_AREAS + bool "Allow no execute kernel areas" + help + Mark areas of the kernel that should never be executed (data, heap + etc.) as no execute. This helps with a certain set of security issues. + You should say Y here unless you like malicious code doing unexpected + things on your hardware. + endmenu menu "Boot options" diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug index 4ee8e90..032ccc1 100644 --- a/arch/arm64/Kconfig.debug +++ b/arch/arm64/Kconfig.debug @@ -43,4 +43,27 @@ config ARM64_RANDOMIZE_TEXT_OFFSET of TEXT_OFFSET and platforms must not require a specific value. +config DEBUG_RODATA + bool "Make kernel text and rodata read-only" + help + If this is set, kernel text and rodata will be made read-only. This + is to help catch accidental or malicious attempts to change the + kernel's executable code. Additionally splits rodata from kernel + text so it can be made explicitly non-executable. + + If in doubt, say Y + +config DEBUG_ALIGN_RODATA + depends on DEBUG_RODATA + bool "Align linker sections up to SECTION_SIZE" + help + If this option is enabled, sections that may potentially be marked as + read only or non-executable will be aligned up to the section size of + the kernel. This prevents sections from being split into pages and + avoids a potential TLB penalty. The downside is an increase in + alignment and potentially wasted space. Turn on this option if + performance is more important than memory pressure. + + If in doubt, say N + endmenu diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h index f2defe1..6e2f910 100644 --- a/arch/arm64/include/asm/cacheflush.h +++ b/arch/arm64/include/asm/cacheflush.h @@ -148,4 +148,7 @@ static inline void flush_cache_vunmap(unsigned long start, unsigned long end) { } +#ifdef CONFIG_DEBUG_RODATA +void mark_rodata_ro(void); +#endif #endif diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 2b674c5..6dea60d 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -8,6 +8,7 @@ #include #include #include +#include #include "image.h" @@ -54,6 +55,9 @@ SECTIONS _text = .; HEAD_TEXT } +#ifdef DEBUG_ALIGN_RODATA + . = ALIGN(1< #include #include +#include #include #include @@ -137,17 +138,55 @@ static void __init *early_alloc(unsigned long sz) return ptr; } -static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr, +/* + * remap a PMD into pages + */ +static noinline void __ref split_pmd(pmd_t *pmd, bool early) +{ + pte_t *pte, *start_pte; + unsigned long pfn; + int i = 0; + + if (early) + start_pte = pte = early_alloc(PTRS_PER_PTE*sizeof(pte_t)); + else + start_pte = pte = (pte_t *)__get_free_page(PGALLOC_GFP); + + BUG_ON(!pte); + + pfn = pmd_pfn(*pmd); + + do { + /* + * Need to have the least restrictive permissions available + * permissions will be fixed up later + */ + set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC)); + pfn++; + } while (pte++, i++, i < PTRS_PER_PTE); + + + __pmd_populate(pmd, __pa(start_pte), PMD_TYPE_TABLE); + flush_tlb_all(); +} + +static void __ref alloc_init_pte(pmd_t *pmd, unsigned long addr, unsigned long end, unsigned long pfn, - pgprot_t prot) + pgprot_t prot, bool early) { pte_t *pte; if (pmd_none(*pmd)) { - pte = early_alloc(PTRS_PER_PTE * sizeof(pte_t)); + if (early) + pte = early_alloc(PTRS_PER_PTE * sizeof(pte_t)); + else + pte = (pte_t *)__get_free_page(PGALLOC_GFP); + BUG_ON(!pte); __pmd_populate(pmd, __pa(pte), PMD_TYPE_TABLE); } - BUG_ON(pmd_bad(*pmd)); + + if (pmd_bad(*pmd)) + split_pmd(pmd, early); pte = pte_offset_kernel(pmd, addr); do { @@ -156,29 +195,52 @@ static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr, } while (pte++, addr += PAGE_SIZE, addr != end); } -static void __init alloc_init_pmd(pud_t *pud, unsigned long addr, +void __ref split_pud(pud_t *old_pud, pmd_t *pmd) +{ + unsigned long pfn = pud_pfn(*old_pud); + const pmdval_t mask = PMD_SECT_USER | PMD_SECT_PXN | PMD_SECT_UXN | + PMD_SECT_RDONLY | PMD_SECT_PROT_NONE | + PMD_SECT_VALID; + pgprot_t prot = __pgprot(pud_val(*old_pud) & mask); + int i = 0; + + do { + set_pmd(pmd, pfn_pmd(pfn, prot)); + pfn++; + } while (pmd++, i++, i < PTRS_PER_PMD); +} + +static void __ref alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end, phys_addr_t phys, - int map_io) + pgprot_t sect_prot, pgprot_t pte_prot, + bool early, int map_io) { pmd_t *pmd; unsigned long next; - pmdval_t prot_sect; - pgprot_t prot_pte; if (map_io) { - prot_sect = PROT_SECT_DEVICE_nGnRE; - prot_pte = __pgprot(PROT_DEVICE_nGnRE); - } else { - prot_sect = PROT_SECT_NORMAL_EXEC; - prot_pte = PAGE_KERNEL_EXEC; + sect_prot = PROT_SECT_DEVICE_nGnRE; + pte_prot = __pgprot(PROT_DEVICE_nGnRE); } /* * Check for initial section mappings in the pgd/pud and remove them. */ if (pud_none(*pud) || pud_bad(*pud)) { - pmd = early_alloc(PTRS_PER_PMD * sizeof(pmd_t)); + if (early) + pmd = early_alloc(PTRS_PER_PMD * sizeof(pmd_t)); + else + pmd = pmd_alloc_one(&init_mm, addr); + BUG_ON(!pmd); + if (pud_sect(*pud)) { + /* + * need to have the 1G of mappings continue to be + * present + */ + split_pud(pud, pmd); + } pud_populate(&init_mm, pud, pmd); + flush_tlb_all(); } pmd = pmd_offset(pud, addr); @@ -186,8 +248,8 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned long addr, next = pmd_addr_end(addr, end); /* try section mapping first */ if (((addr | next | phys) & ~SECTION_MASK) == 0) { - pmd_t old_pmd =*pmd; - set_pmd(pmd, __pmd(phys | prot_sect)); + pmd_t old_pmd = *pmd; + set_pmd(pmd, __pmd(phys | sect_prot)); /* * Check for previous table entries created during * boot (__create_page_tables) and flush them. @@ -196,15 +258,16 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned long addr, flush_tlb_all(); } else { alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys), - prot_pte); + pte_prot, early); } phys += next - addr; } while (pmd++, addr = next, addr != end); } -static void __init alloc_init_pud(pgd_t *pgd, unsigned long addr, +static void __ref alloc_init_pud(pgd_t *pgd, unsigned long addr, unsigned long end, unsigned long phys, - int map_io) + pgprot_t sect_prot, pgprot_t pte_prot, + bool early, int map_io) { pud_t *pud; unsigned long next; @@ -222,10 +285,10 @@ static void __init alloc_init_pud(pgd_t *pgd, unsigned long addr, /* * For 4K granule only, attempt to put down a 1GB block */ - if (!map_io && (PAGE_SHIFT == 12) && + if (!map_io && early && (PAGE_SHIFT == 12) && ((addr | next | phys) & ~PUD_MASK) == 0) { pud_t old_pud = *pud; - set_pud(pud, __pud(phys | PROT_SECT_NORMAL_EXEC)); + set_pud(pud, __pud(phys | sect_prot)); /* * If we have an old value for a pud, it will @@ -240,7 +303,8 @@ static void __init alloc_init_pud(pgd_t *pgd, unsigned long addr, flush_tlb_all(); } } else { - alloc_init_pmd(pud, addr, next, phys, map_io); + alloc_init_pmd(pud, addr, next, phys, sect_prot, + pte_prot, early, map_io); } phys += next - addr; } while (pud++, addr = next, addr != end); @@ -250,9 +314,11 @@ static void __init alloc_init_pud(pgd_t *pgd, unsigned long addr, * Create the page directory entries and any necessary page tables for the * mapping specified by 'md'. */ -static void __init __create_mapping(pgd_t *pgd, phys_addr_t phys, - unsigned long virt, phys_addr_t size, - int map_io) +static void __ref __create_mapping(pgd_t *pgd, phys_addr_t phys, + unsigned long virt, + phys_addr_t size, + pgprot_t sect_prot, pgprot_t pte_prot, + int map_io, bool early) { unsigned long addr, length, end, next; @@ -262,31 +328,140 @@ static void __init __create_mapping(pgd_t *pgd, phys_addr_t phys, end = addr + length; do { next = pgd_addr_end(addr, end); - alloc_init_pud(pgd, addr, next, phys, map_io); + alloc_init_pud(pgd, addr, next, phys, sect_prot, pte_prot, + early, map_io); phys += next - addr; } while (pgd++, addr = next, addr != end); } -static void __init create_mapping(phys_addr_t phys, unsigned long virt, - phys_addr_t size) +void __init create_id_mapping(phys_addr_t addr, phys_addr_t size, int map_io) +{ + if ((addr >> PGDIR_SHIFT) >= ARRAY_SIZE(idmap_pg_dir)) { + pr_warn("BUG: not creating id mapping for %pa\n", &addr); + return; + } + __create_mapping(&idmap_pg_dir[pgd_index(addr)], + addr, addr, size, PROT_SECT_NORMAL_EXEC, + PAGE_KERNEL_EXEC, map_io, false); +} + +static inline pmd_t *pmd_off_k(unsigned long virt) +{ + return pmd_offset(pud_offset(pgd_offset_k(virt), virt), virt); +} + +#ifdef CONFIG_EARLY_PRINTK +/* + * Create an early I/O mapping using the pgd/pmd entries already populated + * in head.S as this function is called too early to allocated any memory. The + * mapping size is 2MB with 4KB pages or 64KB or 64KB pages. + */ +void __iomem * __init early_io_map(phys_addr_t phys, unsigned long virt) +{ + unsigned long size, mask; + bool page64k = IS_ENABLED(CONFIG_ARM64_64K_PAGES); + pgd_t *pgd; + pud_t *pud; + pmd_t *pmd; + pte_t *pte; + + /* + * No early pte entries with !ARM64_64K_PAGES configuration, so using + * sections (pmd). + */ + size = page64k ? PAGE_SIZE : SECTION_SIZE; + mask = ~(size - 1); + + pgd = pgd_offset_k(virt); + pud = pud_offset(pgd, virt); + if (pud_none(*pud)) + return NULL; + pmd = pmd_offset(pud, virt); + + if (page64k) { + if (pmd_none(*pmd)) + return NULL; + pte = pte_offset_kernel(pmd, virt); + set_pte(pte, __pte((phys & mask) | PROT_DEVICE_nGnRE)); + } else { + set_pmd(pmd, __pmd((phys & mask) | PROT_SECT_DEVICE_nGnRE)); + } + + return (void __iomem *)((virt & mask) + (phys & ~mask)); +} +#endif + +static void __ref create_mapping(phys_addr_t phys, unsigned long virt, + phys_addr_t size, + pgprot_t sect_prot, pgprot_t pte_prot) { if (virt < VMALLOC_START) { pr_warn("BUG: not creating mapping for %pa@0x%016lx - outside kernel range\n", &phys, virt); return; } - __create_mapping(pgd_offset_k(virt & PAGE_MASK), phys, virt, size, 0); + + return __create_mapping(pgd_offset_k(virt & PAGE_MASK), phys, virt, + size, sect_prot, pte_prot, 0, true); } -void __init create_id_mapping(phys_addr_t addr, phys_addr_t size, int map_io) +static void __ref create_mapping_late(phys_addr_t phys, unsigned long virt, + phys_addr_t size, + pgprot_t sect_prot, pgprot_t pte_prot) { - if ((addr >> PGDIR_SHIFT) >= ARRAY_SIZE(idmap_pg_dir)) { - pr_warn("BUG: not creating id mapping for %pa\n", &addr); + if (virt < VMALLOC_START) { + pr_warn("BUG: not creating mapping for %pa@0x%016lx - outside kernel range\n", + &phys, virt); return; } - __create_mapping(&idmap_pg_dir[pgd_index(addr)], - addr, addr, size, map_io); + + return __create_mapping(pgd_offset_k(virt & PAGE_MASK), phys, virt, + size, sect_prot, pte_prot, 0, false); +} + +#ifdef CONFIG_NX_KERNEL_AREAS +static void __init __map_memblock(phys_addr_t start, phys_addr_t end) +{ + /* + * Set up the executable regions using the existing section mappings + * for now. This will get more fine grained later once all memory + * is mapped + */ + unsigned long kernel_x_start = round_down(__pa(_stext), SECTION_SIZE); + unsigned long kernel_x_end = round_up(__pa(__init_end), SECTION_SIZE); + + if (end < kernel_x_start) { + create_mapping(start, __phys_to_virt(start), + end - start, PROT_SECT_NORMAL, PAGE_KERNEL); + } else if (start >= kernel_x_end) { + create_mapping(start, __phys_to_virt(start), + end - start, PROT_SECT_NORMAL, PAGE_KERNEL); + } else { + if (start < kernel_x_start) + create_mapping(start, __phys_to_virt(start), + kernel_x_start - start, + PROT_SECT_NORMAL, + PAGE_KERNEL); + create_mapping(kernel_x_start, + __phys_to_virt(kernel_x_start), + kernel_x_end - kernel_x_start, + PROT_SECT_NORMAL_EXEC, PAGE_KERNEL_EXEC); + if (kernel_x_end < end) + create_mapping(kernel_x_end, + __phys_to_virt(kernel_x_end), + end - kernel_x_end, + PROT_SECT_NORMAL, + PAGE_KERNEL); + } + +} +#else +static void __init __map_memblock(phys_addr_t start, phys_addr_t end) +{ + create_mapping(start, __phys_to_virt(start), end - start, + PROT_SECT_NORMAL_EXEC, PAGE_KERNEL_EXEC); } +#endif static void __init map_mem(void) { @@ -328,14 +503,69 @@ static void __init map_mem(void) memblock_set_current_limit(limit); } #endif - - create_mapping(start, __phys_to_virt(start), end - start); + __map_memblock(start, end); } /* Limit no longer required. */ memblock_set_current_limit(MEMBLOCK_ALLOC_ANYWHERE); } +void __init fixup_executable(void) +{ +#ifdef CONFIG_NX_KERNEL_AREAS + /* now that we are actually fully mapped, make the start/end more fine grained */ + if (!IS_ALIGNED((unsigned long)_stext, SECTION_SIZE)) { + unsigned long aligned_start = round_down(__pa(_stext), + SECTION_SIZE); + + create_mapping(aligned_start, __phys_to_virt(aligned_start), + __pa(_stext) - aligned_start, + PROT_SECT_NORMAL, + PAGE_KERNEL); + } + + if (!IS_ALIGNED((unsigned long)__init_end, SECTION_SIZE)) { + unsigned long aligned_end = round_up(__pa(__init_end), + SECTION_SIZE); + create_mapping(__pa(__init_end), (unsigned long)__init_end, + aligned_end - __pa(__init_end), + PROT_SECT_NORMAL, + PAGE_KERNEL); + } +#endif +} + +#ifdef CONFIG_DEBUG_RODATA +void mark_rodata_ro(void) +{ + create_mapping_late(__pa(_stext), (unsigned long)_stext, + (unsigned long)_etext - (unsigned long)_stext, + PROT_SECT_NORMAL_EXEC | PMD_SECT_RDONLY, + PAGE_KERNEL_EXEC | PTE_RDONLY); + +} +#endif + +static int __flush_mappings(void *unused) +{ + flush_tlb_kernel_range((unsigned long)__init_begin, + (unsigned long)__init_end); + return 0; +} + +void __ref fixup_init(void) +{ + phys_addr_t start = __pa(__init_begin); + phys_addr_t end = __pa(__init_end); + + create_mapping_late(start, (unsigned long)__init_begin, + end - start, + PROT_SECT_NORMAL, + PAGE_KERNEL); + if (!IS_ALIGNED(start, SECTION_SIZE) || !IS_ALIGNED(end, SECTION_SIZE)) + stop_machine(__flush_mappings, NULL, NULL); +} + /* * paging_init() sets up the page tables, initialises the zone memory * maps and sets up the zero page. @@ -345,6 +575,7 @@ void __init paging_init(void) void *zero_page; map_mem(); + fixup_executable(); /* * Finally flush the caches and tlb to ensure that we're in a -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation