Subject: [PATCH v5sub1 7/8] arm64: move kernel image to base of vmalloc area

From: [email-masked] (Mark Rutland)
Date: Mon, 1 Feb 2016 14:32:26 +0000

On Mon, Feb 01, 2016 at 11:54:52AM +0100, Ard Biesheuvel wrote:
> This moves the module area to right before the vmalloc area, and
> moves the kernel image to the base of the vmalloc area. This is
> an intermediate step towards implementing KASLR, which allows the
> kernel image to be located anywhere in the vmalloc area.
> 
> Signed-off-by: Ard Biesheuvel <[email-masked]>

With the fix for the issue Catalin spotted:

Reviewed-by: Mark Rutland <[email-masked]>

Mark.

> ---
>  arch/arm64/include/asm/kasan.h   |  2 +-
>  arch/arm64/include/asm/memory.h  | 21 +++--
>  arch/arm64/include/asm/pgtable.h | 10 +-
>  arch/arm64/mm/dump.c             | 12 +--
>  arch/arm64/mm/init.c             | 23 ++---
>  arch/arm64/mm/kasan_init.c       | 31 ++++++-
>  arch/arm64/mm/mmu.c              | 97 +++++++++++++-------
>  7 files changed, 129 insertions(+), 67 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kasan.h b/arch/arm64/include/asm/kasan.h
> index de0d21211c34..71ad0f93eb71 100644
> --- a/arch/arm64/include/asm/kasan.h
> +++ b/arch/arm64/include/asm/kasan.h
> @@ -14,7 +14,7 @@
>   * KASAN_SHADOW_END: KASAN_SHADOW_START + 1/8 of kernel virtual addresses.
>   */
>  #define KASAN_SHADOW_START      (VA_START)
> -#define KASAN_SHADOW_END        (KASAN_SHADOW_START + (1UL << (VA_BITS - 3)))
> +#define KASAN_SHADOW_END        (KASAN_SHADOW_START + KASAN_SHADOW_SIZE)
>  
>  /*
>   * This value is used to map an address to the corresponding shadow
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index aebc739f5a11..4388651d1f0d 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -45,16 +45,15 @@
>   * VA_START - the first kernel virtual address.
>   * TASK_SIZE - the maximum size of a user space task.
>   * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area.
> - * The module space lives between the addresses given by TASK_SIZE
> - * and PAGE_OFFSET - it must be within 128MB of the kernel text.
>   */
>  #define VA_BITS			(CONFIG_ARM64_VA_BITS)
>  #define VA_START		(UL(0xffffffffffffffff) << VA_BITS)
>  #define PAGE_OFFSET		(UL(0xffffffffffffffff) << (VA_BITS - 1))
> -#define KIMAGE_VADDR		(PAGE_OFFSET)
> -#define MODULES_END		(KIMAGE_VADDR)
> -#define MODULES_VADDR		(MODULES_END - SZ_64M)
> -#define PCI_IO_END		(MODULES_VADDR - SZ_2M)
> +#define KIMAGE_VADDR		(MODULES_END)
> +#define MODULES_END		(MODULES_VADDR + MODULES_VSIZE)
> +#define MODULES_VADDR		(VA_START + KASAN_SHADOW_SIZE)
> +#define MODULES_VSIZE		(SZ_64M)
> +#define PCI_IO_END		(PAGE_OFFSET - SZ_2M)
>  #define PCI_IO_START		(PCI_IO_END - PCI_IO_SIZE)
>  #define FIXADDR_TOP		(PCI_IO_START - SZ_2M)
>  #define TASK_SIZE_64		(UL(1) << VA_BITS)
> @@ -72,6 +71,16 @@
>  #define TASK_UNMAPPED_BASE	(PAGE_ALIGN(TASK_SIZE / 4))
>  
>  /*
> + * The size of the KASAN shadow region. This should be 1/8th of the
> + * size of the entire kernel virtual address space.
> + */
> +#ifdef CONFIG_KASAN
> +#define KASAN_SHADOW_SIZE	(UL(1) << (VA_BITS - 3))
> +#else
> +#define KASAN_SHADOW_SIZE	(0)
> +#endif
> +
> +/*
>   * Physical vs virtual RAM address space conversion.  These are
>   * private definitions which should NOT be used outside memory.h
>   * files.  Use virt_to_phys/phys_to_virt/__pa/__va instead.
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 87355408d448..a440f5a85d08 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -36,19 +36,13 @@
>   *
>   * VMEMAP_SIZE: allows the whole VA space to be covered by a struct page array
>   *	(rounded up to PUD_SIZE).
> - * VMALLOC_START: beginning of the kernel VA space
> + * VMALLOC_START: beginning of the kernel vmalloc space
>   * VMALLOC_END: extends to the available space below vmmemmap, PCI I/O space,
>   *	fixed mappings and modules
>   */
>  #define VMEMMAP_SIZE		ALIGN((1UL << (VA_BITS - PAGE_SHIFT)) * sizeof(struct page), PUD_SIZE)
>  
> -#ifndef CONFIG_KASAN
> -#define VMALLOC_START		(VA_START)
> -#else
> -#include <asm/kasan.h>
> -#define VMALLOC_START		(KASAN_SHADOW_END + SZ_64K)
> -#endif
> -
> +#define VMALLOC_START		(MODULES_END)
>  #define VMALLOC_END		(PAGE_OFFSET - PUD_SIZE - VMEMMAP_SIZE - SZ_64K)
>  
>  #define vmemmap			((struct page *)(VMALLOC_END + SZ_64K))
> diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c
> index 0adbebbc2803..e83ffb00560c 100644
> --- a/arch/arm64/mm/dump.c
> +++ b/arch/arm64/mm/dump.c
> @@ -35,7 +35,9 @@ struct addr_marker {
>  };
>  
>  enum address_markers_idx {
> -	VMALLOC_START_NR = 0,
> +	MODULES_START_NR = 0,
> +	MODULES_END_NR,
> +	VMALLOC_START_NR,
>  	VMALLOC_END_NR,
>  #ifdef CONFIG_SPARSEMEM_VMEMMAP
>  	VMEMMAP_START_NR,
> @@ -45,12 +47,12 @@ enum address_markers_idx {
>  	FIXADDR_END_NR,
>  	PCI_START_NR,
>  	PCI_END_NR,
> -	MODULES_START_NR,
> -	MODULES_END_NR,
>  	KERNEL_SPACE_NR,
>  };
>  
>  static struct addr_marker address_markers[] = {
> +	{ MODULES_VADDR,	"Modules start" },
> +	{ MODULES_END,		"Modules end" },
>  	{ VMALLOC_START,	"vmalloc() Area" },
>  	{ VMALLOC_END,		"vmalloc() End" },
>  #ifdef CONFIG_SPARSEMEM_VMEMMAP
> @@ -61,9 +63,7 @@ static struct addr_marker address_markers[] = {
>  	{ FIXADDR_TOP,		"Fixmap end" },
>  	{ PCI_IO_START,		"PCI I/O start" },
>  	{ PCI_IO_END,		"PCI I/O end" },
> -	{ MODULES_VADDR,	"Modules start" },
> -	{ MODULES_END,		"Modules end" },
> -	{ PAGE_OFFSET,		"Kernel Mapping" },
> +	{ PAGE_OFFSET,		"Linear Mapping" },
>  	{ -1,			NULL },
>  };
>  
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index f3b061e67bfe..1d627cd8121c 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -36,6 +36,7 @@
>  #include <linux/swiotlb.h>
>  
>  #include <asm/fixmap.h>
> +#include <asm/kasan.h>
>  #include <asm/memory.h>
>  #include <asm/sections.h>
>  #include <asm/setup.h>
> @@ -302,22 +303,26 @@ void __init mem_init(void)
>  #ifdef CONFIG_KASAN
>  		  "    kasan   : 0x%16lx - 0x%16lx   (%6ld GB)\n"
>  #endif
> +		  "    modules : 0x%16lx - 0x%16lx   (%6ld MB)\n"
>  		  "    vmalloc : 0x%16lx - 0x%16lx   (%6ld GB)\n"
> +		  "      .init : 0x%p" " - 0x%p" "   (%6ld KB)\n"
> +		  "      .text : 0x%p" " - 0x%p" "   (%6ld KB)\n"
> +		  "      .data : 0x%p" " - 0x%p" "   (%6ld KB)\n"
>  #ifdef CONFIG_SPARSEMEM_VMEMMAP
>  		  "    vmemmap : 0x%16lx - 0x%16lx   (%6ld GB maximum)\n"
>  		  "              0x%16lx - 0x%16lx   (%6ld MB actual)\n"
>  #endif
>  		  "    fixed   : 0x%16lx - 0x%16lx   (%6ld KB)\n"
>  		  "    PCI I/O : 0x%16lx - 0x%16lx   (%6ld MB)\n"
> -		  "    modules : 0x%16lx - 0x%16lx   (%6ld MB)\n"
> -		  "    memory  : 0x%16lx - 0x%16lx   (%6ld MB)\n"
> -		  "      .init : 0x%p" " - 0x%p" "   (%6ld KB)\n"
> -		  "      .text : 0x%p" " - 0x%p" "   (%6ld KB)\n"
> -		  "      .data : 0x%p" " - 0x%p" "   (%6ld KB)\n",
> +		  "    memory  : 0x%16lx - 0x%16lx   (%6ld MB)\n",
>  #ifdef CONFIG_KASAN
>  		  MLG(KASAN_SHADOW_START, KASAN_SHADOW_END),
>  #endif
> +		  MLM(MODULES_VADDR, MODULES_END),
>  		  MLG(VMALLOC_START, VMALLOC_END),
> +		  MLK_ROUNDUP(__init_begin, __init_end),
> +		  MLK_ROUNDUP(_text, _etext),
> +		  MLK_ROUNDUP(_sdata, _edata),
>  #ifdef CONFIG_SPARSEMEM_VMEMMAP
>  		  MLG((unsigned long)vmemmap,
>  		      (unsigned long)vmemmap + VMEMMAP_SIZE),
> @@ -326,11 +331,7 @@ void __init mem_init(void)
>  #endif
>  		  MLK(FIXADDR_START, FIXADDR_TOP),
>  		  MLM(PCI_IO_START, PCI_IO_END),
> -		  MLM(MODULES_VADDR, MODULES_END),
> -		  MLM(PAGE_OFFSET, (unsigned long)high_memory),
> -		  MLK_ROUNDUP(__init_begin, __init_end),
> -		  MLK_ROUNDUP(_text, _etext),
> -		  MLK_ROUNDUP(_sdata, _edata));
> +		  MLM(PAGE_OFFSET, (unsigned long)high_memory));
>  
>  #undef MLK
>  #undef MLM
> @@ -358,8 +359,8 @@ void __init mem_init(void)
>  
>  void free_initmem(void)
>  {
> -	fixup_init();
>  	free_initmem_default(0);
> +	fixup_init();
>  }
>  
>  #ifdef CONFIG_BLK_DEV_INITRD
> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> index cc569a38bc76..66c246871d2e 100644
> --- a/arch/arm64/mm/kasan_init.c
> +++ b/arch/arm64/mm/kasan_init.c
> @@ -17,9 +17,11 @@
>  #include <linux/start_kernel.h>
>  
>  #include <asm/mmu_context.h>
> +#include <asm/kernel-pgtable.h>
>  #include <asm/page.h>
>  #include <asm/pgalloc.h>
>  #include <asm/pgtable.h>
> +#include <asm/sections.h>
>  #include <asm/tlbflush.h>
>  
>  static pgd_t tmp_pg_dir[PTRS_PER_PGD] __initdata __aligned(PGD_SIZE);
> @@ -33,7 +35,7 @@ static void __init kasan_early_pte_populate(pmd_t *pmd, unsigned long addr,
>  	if (pmd_none(*pmd))
>  		pmd_populate_kernel(&init_mm, pmd, kasan_zero_pte);
>  
> -	pte = pte_offset_kernel(pmd, addr);
> +	pte = pte_offset_kimg(pmd, addr);
>  	do {
>  		next = addr + PAGE_SIZE;
>  		set_pte(pte, pfn_pte(virt_to_pfn(kasan_zero_page),
> @@ -51,7 +53,7 @@ static void __init kasan_early_pmd_populate(pud_t *pud,
>  	if (pud_none(*pud))
>  		pud_populate(&init_mm, pud, kasan_zero_pmd);
>  
> -	pmd = pmd_offset(pud, addr);
> +	pmd = pmd_offset_kimg(pud, addr);
>  	do {
>  		next = pmd_addr_end(addr, end);
>  		kasan_early_pte_populate(pmd, addr, next);
> @@ -68,7 +70,7 @@ static void __init kasan_early_pud_populate(pgd_t *pgd,
>  	if (pgd_none(*pgd))
>  		pgd_populate(&init_mm, pgd, kasan_zero_pud);
>  
> -	pud = pud_offset(pgd, addr);
> +	pud = pud_offset_kimg(pgd, addr);
>  	do {
>  		next = pud_addr_end(addr, end);
>  		kasan_early_pmd_populate(pud, addr, next);
> @@ -126,9 +128,13 @@ static void __init clear_pgds(unsigned long start,
>  
>  void __init kasan_init(void)
>  {
> +	u64 kimg_shadow_start, kimg_shadow_end;
>  	struct memblock_region *reg;
>  	int i;
>  
> +	kimg_shadow_start = (u64)kasan_mem_to_shadow(_text);
> +	kimg_shadow_end = (u64)kasan_mem_to_shadow(_end);
> +
>  	/*
>  	 * We are going to perform proper setup of shadow memory.
>  	 * At first we should unmap early shadow (clear_pgds() call bellow).
> @@ -142,8 +148,25 @@ void __init kasan_init(void)
>  
>  	clear_pgds(KASAN_SHADOW_START, KASAN_SHADOW_END);
>  
> +	vmemmap_populate(kimg_shadow_start, kimg_shadow_end, NUMA_NO_NODE);
> +
> +	/*
> +	 * vmemmap_populate() has populated the shadow region that covers the
> +	 * kernel image with SWAPPER_BLOCK_SIZE mappings, so we have to round
> +	 * the start and end addresses to SWAPPER_BLOCK_SIZE as well, to prevent
> +	 * kasan_populate_zero_shadow() from replacing the PMD block mappings
> +	 * with PMD table mappings at the edges of the shadow region for the
> +	 * kernel image.
> +	 */
> +	if (ARM64_SWAPPER_USES_SECTION_MAPS) {
> +		kimg_shadow_start = round_down(kimg_shadow_start,
> +					       SWAPPER_BLOCK_SIZE);
> +		kimg_shadow_end = round_up(kimg_shadow_end, SWAPPER_BLOCK_SIZE);
> +	}
>  	kasan_populate_zero_shadow((void *)KASAN_SHADOW_START,
> -			kasan_mem_to_shadow((void *)MODULES_VADDR));
> +				   (void *)kimg_shadow_start);
> +	kasan_populate_zero_shadow((void *)kimg_shadow_end,
> +				   kasan_mem_to_shadow((void *)PAGE_OFFSET));
>  
>  	for_each_memblock(memory, reg) {
>  		void *start = (void *)__phys_to_virt(reg->base);
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index b84915723ea0..4c4b15932963 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -53,6 +53,10 @@ u64 idmap_t0sz = TCR_T0SZ(VA_BITS);
>  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;
> +static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss;
> +static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss;
> +
>  pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
>  			      unsigned long size, pgprot_t vma_prot)
>  {
> @@ -349,14 +353,14 @@ static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end
>  {
>  
>  	unsigned long kernel_start = __pa(_stext);
> -	unsigned long kernel_end = __pa(_end);
> +	unsigned long kernel_end = __pa(_etext);
>  
>  	/*
> -	 * The kernel itself is mapped at page granularity. Map all other
> -	 * memory, making sure we don't overwrite the existing kernel mappings.
> +	 * Take care not to create a writable alias for the
> +	 * read-only text and rodata sections of the kernel image.
>  	 */
>  
> -	/* No overlap with the kernel. */
> +	/* No overlap with the kernel text */
>  	if (end < kernel_start || start >= kernel_end) {
>  		__create_pgd_mapping(pgd, start, __phys_to_virt(start),
>  				     end - start, PAGE_KERNEL,
> @@ -365,7 +369,7 @@ static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end
>  	}
>  
>  	/*
> -	 * This block overlaps the kernel mapping. Map the portion(s) which
> +	 * This block overlaps the kernel text mapping. Map the portion(s) which
>  	 * don't overlap.
>  	 */
>  	if (start < kernel_start)
> @@ -398,25 +402,28 @@ static void __init map_mem(pgd_t *pgd)
>  	}
>  }
>  
> -#ifdef CONFIG_DEBUG_RODATA
>  void mark_rodata_ro(void)
>  {
> +	if (!IS_ENABLED(CONFIG_DEBUG_RODATA))
> +		return;
> +
>  	create_mapping_late(__pa(_stext), (unsigned long)_stext,
>  				(unsigned long)_etext - (unsigned long)_stext,
>  				PAGE_KERNEL_ROX);
> -
>  }
> -#endif
>  
>  void fixup_init(void)
>  {
> -	create_mapping_late(__pa(__init_begin), (unsigned long)__init_begin,
> -			(unsigned long)__init_end - (unsigned long)__init_begin,
> -			PAGE_KERNEL);
> +	/*
> +	 * Unmap the __init region but leave the VM area in place. This
> +	 * prevents the region from being reused for kernel modules, which
> +	 * is not supported by kallsyms.
> +	 */
> +	unmap_kernel_range((u64)__init_begin, (u64)(__init_end - __init_begin));
>  }
>  
>  static void __init map_kernel_chunk(pgd_t *pgd, void *va_start, void *va_end,
> -				    pgprot_t prot)
> +				    pgprot_t prot, struct vm_struct *vma)
>  {
>  	phys_addr_t pa_start = __pa(va_start);
>  	unsigned long size = va_end - va_start;
> @@ -426,6 +433,14 @@ static void __init map_kernel_chunk(pgd_t *pgd, void *va_start, void *va_end,
>  
>  	__create_pgd_mapping(pgd, pa_start, (unsigned long)va_start, size, prot,
>  			     early_pgtable_alloc);
> +
> +	vma->addr	= va_start;
> +	vma->phys_addr	= pa_start;
> +	vma->size	= size;
> +	vma->flags	= VM_MAP;
> +	vma->caller	= map_kernel_chunk;
> +
> +	vm_area_add_early(vma);
>  }
>  
>  /*
> @@ -433,17 +448,35 @@ static void __init map_kernel_chunk(pgd_t *pgd, void *va_start, void *va_end,
>   */
>  static void __init map_kernel(pgd_t *pgd)
>  {
> +	static struct vm_struct vmlinux_text, vmlinux_init, vmlinux_data;
>  
> -	map_kernel_chunk(pgd, _stext, _etext, PAGE_KERNEL_EXEC);
> -	map_kernel_chunk(pgd, __init_begin, __init_end, PAGE_KERNEL_EXEC);
> -	map_kernel_chunk(pgd, _data, _end, PAGE_KERNEL);
> +	map_kernel_chunk(pgd, _stext, _etext, PAGE_KERNEL_EXEC, &vmlinux_text);
> +	map_kernel_chunk(pgd, __init_begin, __init_end, PAGE_KERNEL_EXEC,
> +			 &vmlinux_init);
> +	map_kernel_chunk(pgd, _data, _end, PAGE_KERNEL, &vmlinux_data);
>  
> -	/*
> -	 * The fixmap falls in a separate pgd to the kernel, and doesn't live
> -	 * in the carveout for the swapper_pg_dir. We can simply re-use the
> -	 * existing dir for the fixmap.
> -	 */
> -	set_pgd(pgd_offset_raw(pgd, FIXADDR_START), *pgd_offset_k(FIXADDR_START));
> +	if (!pgd_val(*pgd_offset_raw(pgd, FIXADDR_START))) {
> +		/*
> +		 * The fixmap falls in a separate pgd to the kernel, and doesn't
> +		 * live in the carveout for the swapper_pg_dir. We can simply
> +		 * re-use the existing dir for the fixmap.
> +		 */
> +		set_pgd(pgd_offset_raw(pgd, FIXADDR_START),
> +			*pgd_offset_k(FIXADDR_START));
> +	} else if (CONFIG_PGTABLE_LEVELS > 3) {
> +		/*
> +		 * The fixmap shares its top level pgd entry with the kernel
> +		 * mapping. This can really only occur when we are running
> +		 * with 16k/4 levels, so we can simply reuse the pud level
> +		 * entry instead.
> +		 */
> +		BUG_ON(!IS_ENABLED(CONFIG_ARM64_16K_PAGES));
> +		set_pud(pud_set_fixmap_offset(pgd, FIXADDR_START),
> +			__pud(__pa(bm_pmd) | PUD_TYPE_TABLE));
> +		pud_clear_fixmap();
> +	} else {
> +		BUG();
> +	}
>  
>  	kasan_copy_shadow(pgd);
>  }
> @@ -569,14 +602,6 @@ void vmemmap_free(unsigned long start, unsigned long end)
>  }
>  #endif	/* CONFIG_SPARSEMEM_VMEMMAP */
>  
> -static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss;
> -#if CONFIG_PGTABLE_LEVELS > 2
> -static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss;
> -#endif
> -#if CONFIG_PGTABLE_LEVELS > 3
> -static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss;
> -#endif
> -
>  static inline pud_t * fixmap_pud(unsigned long addr)
>  {
>  	pgd_t *pgd = pgd_offset_k(addr);
> @@ -608,8 +633,18 @@ void __init early_fixmap_init(void)
>  	unsigned long addr = FIXADDR_START;
>  
>  	pgd = pgd_offset_k(addr);
> -	pgd_populate(&init_mm, pgd, bm_pud);
> -	pud = fixmap_pud(addr);
> +	if (CONFIG_PGTABLE_LEVELS > 3 && !pgd_none(*pgd)) {
> +		/*
> +		 * We only end up here if the kernel mapping and the fixmap
> +		 * share the top level pgd entry, which should only happen on
> +		 * 16k/4 levels configurations.
> +		 */
> +		BUG_ON(!IS_ENABLED(CONFIG_ARM64_16K_PAGES));
> +		pud = pud_offset_kimg(pgd, addr);
> +	} else {
> +		pgd_populate(&init_mm, pgd, bm_pud);
> +		pud = fixmap_pud(addr);
> +	}
>  	pud_populate(&init_mm, pud, bm_pmd);
>  	pmd = fixmap_pmd(addr);
>  	pmd_populate_kernel(&init_mm, pmd, bm_pte);
> -- 
> 2.5.0
>