From mboxrd@z Thu Jan 1 00:00:00 1970 From: lauraa@codeaurora.org (Laura Abbott) Date: Mon, 2 Jun 2014 13:57:38 -0700 Subject: [PATCHv2 4/4] arm64: add better page protections to arm64 In-Reply-To: <1401742658-11841-1-git-send-email-lauraa@codeaurora.org> References: <1401742658-11841-1-git-send-email-lauraa@codeaurora.org> Message-ID: <1401742658-11841-5-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 or in progress for arm. This is for security reasons. The flow is currently: - 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.debug | 23 ++++++ arch/arm64/kernel/vmlinux.lds.S | 17 ++++ arch/arm64/mm/init.c | 1 + arch/arm64/mm/mm.h | 2 + arch/arm64/mm/mmu.c | 173 ++++++++++++++++++++++++++++++++++++---- 5 files changed, 200 insertions(+), 16 deletions(-) diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug index 53979ac..f51f3af 100644 --- a/arch/arm64/Kconfig.debug +++ b/arch/arm64/Kconfig.debug @@ -48,4 +48,27 @@ config DEBUG_SET_MODULE_RONX against certain classes of kernel exploits. If in doubt, say "N". +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/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 4ba7a55..7643ae6 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -8,6 +8,7 @@ #include #include #include +#include #define ARM_EXIT_KEEP(x) #define ARM_EXIT_DISCARD(x) x @@ -52,6 +53,9 @@ SECTIONS _text = .; HEAD_TEXT } +#ifdef DEBUG_ALIGN_RODATA + . = ALIGN(1< #include #include +#include #include #include @@ -167,26 +168,67 @@ static void __init *early_alloc(unsigned long sz) return ptr; } -static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr, - unsigned long end, unsigned long pfn) +/* + * remap a PMD into pages + */ +static noinline void __ref split_pmd(pmd_t *pmd, pgprot_t prot, bool early) +{ + pte_t *pte, *start_pte; + u64 val; + unsigned long pfn; + int i = 0; + + val = pmd_val(*pmd); + + 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 = __phys_to_pfn(val & PHYS_MASK); + + do { + 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, 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, prot, early); pte = pte_offset_kernel(pmd, addr); do { - set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC)); + set_pte(pte, pfn_pte(pfn, prot)); pfn++; } while (pte++, addr += PAGE_SIZE, addr != end); } -static void __init alloc_init_pmd(pud_t *pud, unsigned long addr, - unsigned long end, phys_addr_t phys) +static void __ref alloc_init_pmd(pud_t *pud, unsigned long addr, + unsigned long end, phys_addr_t phys, + pgprot_t sect_prot, pgprot_t pte_prot, + bool early) { pmd_t *pmd; unsigned long next; @@ -195,7 +237,11 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned long addr, * 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); pud_populate(&init_mm, pud, pmd); } @@ -213,21 +259,25 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned long addr, if (!pmd_none(old_pmd)) flush_tlb_all(); } else { - alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys)); + alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys), + pte_prot, early); } phys += next - addr; } while (pmd++, addr = next, addr != end); } -static void __init alloc_init_pud(pgd_t *pgd, unsigned long addr, - unsigned long end, unsigned long phys) +static void __ref alloc_init_pud(pgd_t *pgd, unsigned long addr, + unsigned long end, unsigned long phys, + pgprot_t sect_prot, pgprot_t pte_prot, + bool early) { pud_t *pud = pud_offset(pgd, addr); unsigned long next; do { next = pud_addr_end(addr, end); - alloc_init_pmd(pud, addr, next, phys); + alloc_init_pmd(pud, addr, next, phys, sect_prot, pte_prot, + early); phys += next - addr; } while (pud++, addr = next, addr != end); } @@ -236,8 +286,10 @@ 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(phys_addr_t phys, unsigned long virt, - phys_addr_t size) +static void __ref __create_mapping(phys_addr_t phys, unsigned long virt, + phys_addr_t size, + pgprot_t sect_prot, pgprot_t pte_prot, + bool early) { unsigned long addr, length, end, next; pgd_t *pgd; @@ -255,15 +307,37 @@ static void __init create_mapping(phys_addr_t phys, unsigned long virt, end = addr + length; do { next = pgd_addr_end(addr, end); - alloc_init_pud(pgd, addr, next, phys); + alloc_init_pud(pgd, addr, next, phys, sect_prot, pte_prot, + early); phys += next - addr; } while (pgd++, addr = next, addr != end); } +static void __ref create_mapping(phys_addr_t phys, unsigned long virt, + phys_addr_t size, + pgprot_t sect_prot, pgprot_t pte_prot) +{ + return __create_mapping(phys, virt, size, sect_prot, pte_prot, true); +} + +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) +{ + return __create_mapping(phys, virt, size, sect_prot, pte_prot, false); +} + static void __init map_mem(void) { struct memblock_region *reg; phys_addr_t limit; + /* + * Set up the executable regions using the exising section mappings + * foir 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); /* * Temporarily limit the memblock range. We need to do this as @@ -301,13 +375,79 @@ static void __init map_mem(void) } #endif - create_mapping(start, __phys_to_virt(start), end - start); + if (end < kernel_x_start) { + create_mapping(start, __phys_to_virt(start), end - start, + prot_sect_kernel, pgprot_default); + } else if (start >= kernel_x_end) { + create_mapping(start, __phys_to_virt(start), end - start, + prot_sect_kernel | PMD_SECT_PXN, pgprot_default | PTE_PXN); + } else { + if (start < kernel_x_start) + create_mapping(start, __phys_to_virt(start), kernel_x_start - start, + prot_sect_kernel | PMD_SECT_PXN, pgprot_default | PTE_PXN); + create_mapping(kernel_x_start, __phys_to_virt(kernel_x_start), kernel_x_end - kernel_x_start, + prot_sect_kernel, pgprot_default); + if (kernel_x_end < end) + create_mapping(kernel_x_end, __phys_to_virt(kernel_x_end), end - kernel_x_end, + prot_sect_kernel | PMD_SECT_PXN, pgprot_default | PTE_PXN); + + + } + } /* Limit no longer required. */ memblock_set_current_limit(MEMBLOCK_ALLOC_ANYWHERE); } +void __init fixup_executable(void) +{ + /* 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_kernel | PMD_SECT_PXN, + pgprot_default | PTE_PXN); + } + + 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_kernel | PMD_SECT_PXN, pgprot_default | PTE_PXN); + } +} + +#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_kernel | PMD_SECT_RDONLY, + pgprot_default | 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_kernel | PMD_SECT_PXN, pgprot_default | PTE_PXN); + 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. @@ -317,6 +457,7 @@ 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