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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC 22/22] x86/kaslr: Add option to extend KASLR range from 1GB to 3GB
On 07/18/17 at 03:33pm, Thomas Garnier wrote:
> quiet_cmd_relocs = RELOCS $@
> cmd_relocs = $(CMD_RELOCS) $< > $@;$(CMD_RELOCS) --abs-relocs $<
> $(obj)/vmlinux.relocs: vmlinux FORCE
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index a0838ab929f2..0a0c80ab1842 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -170,10 +170,18 @@ void __puthex(unsigned long value)
> }
>
> #if CONFIG_X86_NEED_RELOCS
> +
> +/* Large randomization go lower than -2G and use large relocation table */
> +#ifdef CONFIG_RANDOMIZE_BASE_LARGE
> +typedef long rel_t;
> +#else
> +typedef int rel_t;
> +#endif
> +
> static void handle_relocations(void *output, unsigned long output_len,
> unsigned long virt_addr)
> {
> - int *reloc;
> + rel_t *reloc;
> unsigned long delta, map, ptr;
> unsigned long min_addr = (unsigned long)output;
> unsigned long max_addr = min_addr + (VO___bss_start - VO__text);
> diff --git a/arch/x86/include/asm/page_64_types.h
> b/arch/x86/include/asm/page_64_types.h
> index 3f5f08b010d0..6b65f846dd64 100644
> --- a/arch/x86/include/asm/page_64_types.h
> +++ b/arch/x86/include/asm/page_64_types.h
> @@ -48,7 +48,11 @@
> #define __PAGE_OFFSET __PAGE_OFFSET_BASE
> #endif /* CONFIG_RANDOMIZE_MEMORY */
>
> +#ifdef CONFIG_RANDOMIZE_BASE_LARGE
> +#define __START_KERNEL_map _AC(0xffffffff00000000, UL)
> +#else
> #define __START_KERNEL_map _AC(0xffffffff80000000, UL)
> +#endif /* CONFIG_RANDOMIZE_BASE_LARGE */
>
> /* See Documentation/x86/x86_64/mm.txt for a description of the memory map.
> */
> #ifdef CONFIG_X86_5LEVEL
> @@ -65,9 +69,14 @@
> * 512MiB by default, leaving 1.5GiB for modules once the page tables
> * are fully set up. If kernel ASLR is configured, it can extend the
> * kernel page table mapping, reducing the size of the modules area.
> + * On PIE, we relocate the binary 2G lower so add this extra space.
> */
> #if defined(CONFIG_RANDOMIZE_BASE)
> +#ifdef CONFIG_RANDOMIZE_BASE_LARGE
> +#define KERNEL_IMAGE_SIZE (_AC(3, UL) * 1024 * 1024 * 1024)
> +#else
> #define KERNEL_IMAGE_SIZE (1024 * 1024 * 1024)
> +#endif
> #else
> #define KERNEL_IMAGE_SIZE (512 * 1024 * 1024)
> #endif
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 4103e90ff128..235c3f7b46c7 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -39,6 +39,7 @@ static unsigned int __initdata next_early_pgt;
> pmdval_t early_pmd_flags = __PAGE_KERNEL_LARGE & ~(_PAGE_GLOBAL | _PAGE_NX);
>
> #define __head __section(.head.text)
> +#define pud_count(x) (((x + (PUD_SIZE - 1)) & ~(PUD_SIZE - 1)) >>
> PUD_SHIFT)
>
> static void __head *fixup_pointer(void *ptr, unsigned long physaddr)
> {
> @@ -54,6 +55,8 @@ unsigned long _text_offset = (unsigned long)(_text -
> __START_KERNEL_map);
> void __head notrace __startup_64(unsigned long physaddr)
> {
> unsigned long load_delta, *p;
> + unsigned long level3_kernel_start, level3_kernel_count;
> + unsigned long level3_fixmap_start;
> pgdval_t *pgd;
> p4dval_t *p4d;
> pudval_t *pud;
> @@ -74,6 +77,11 @@ void __head notrace __startup_64(unsigned long physaddr)
> if (load_delta & ~PMD_PAGE_MASK)
> for (;;);
>
> + /* Look at the randomization spread to adapt page table used */
> + level3_kernel_start = pud_index(__START_KERNEL_map);
> + level3_kernel_count = pud_count(KERNEL_IMAGE_SIZE);
> + level3_fixmap_start = level3_kernel_start + level3_kernel_count;
> +
> /* Fixup the physical addresses in the page table */
>
> pgd = fixup_pointer(&early_top_pgt, physaddr);
> @@ -85,8 +93,9 @@ void __head notrace __startup_64(unsigned long physaddr)
> }
>
> pud = fixup_pointer(&level3_kernel_pgt, physaddr);
> - pud[510] += load_delta;
> - pud[511] += load_delta;
> + for (i = 0; i < level3_kernel_count; i++)
> + pud[level3_kernel_start + i] += load_delta;
> + pud[level3_fixmap_start] += load_delta;
>
> pmd = fixup_pointer(level2_fixmap_pgt, physaddr);
> pmd[506] += load_delta;
> @@ -137,7 +146,7 @@ void __head notrace __startup_64(unsigned long physaddr)
> */
>
> pmd = fixup_pointer(level2_kernel_pgt, physaddr);
> - for (i = 0; i < PTRS_PER_PMD; i++) {
> + for (i = 0; i < PTRS_PER_PMD * level3_kernel_count; i++) {
> if (pmd[i] & _PAGE_PRESENT)
> pmd[i] += load_delta;
Wow, this is dangerous. Three pud entries of level3_kernel_pgt all point
to level2_kernel_pgt, it's out of bound of level2_kernel_pgt and
overwrite the next data.
And if only use one page for level2_kernel_pgt, and kernel is randomized
to cross the pud entry of -4G to -1G, it won't work well.
> }
> @@ -268,7 +277,8 @@ asmlinkage __visible void __init x86_64_start_kernel(char
> * real_mode_data)
> */
> BUILD_BUG_ON(MODULES_VADDR < __START_KERNEL_map);
> BUILD_BUG_ON(MODULES_VADDR - __START_KERNEL_map < KERNEL_IMAGE_SIZE);
> - BUILD_BUG_ON(MODULES_LEN + KERNEL_IMAGE_SIZE > 2*PUD_SIZE);
> + BUILD_BUG_ON(!IS_ENABLED(CONFIG_RANDOMIZE_BASE_LARGE) &&
> + MODULES_LEN + KERNEL_IMAGE_SIZE > 2*PUD_SIZE);
> BUILD_BUG_ON((__START_KERNEL_map & ~PMD_MASK) != 0);
> BUILD_BUG_ON((MODULES_VADDR & ~PMD_MASK) != 0);
> BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL));
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index 4d0a7e68bfe8..e8b2d6706eca 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -39,11 +39,15 @@
>
> #define p4d_index(x) (((x) >> P4D_SHIFT) & (PTRS_PER_P4D-1))
> #define pud_index(x) (((x) >> PUD_SHIFT) & (PTRS_PER_PUD-1))
> +#define pud_count(x) (((x + (PUD_SIZE - 1)) & ~(PUD_SIZE - 1)) >>
> PUD_SHIFT)
>
> PGD_PAGE_OFFSET = pgd_index(__PAGE_OFFSET_BASE)
> PGD_START_KERNEL = pgd_index(__START_KERNEL_map)
> L3_START_KERNEL = pud_index(__START_KERNEL_map)
>
> +/* Adapt page table L3 space based on range of randomization */
> +L3_KERNEL_ENTRY_COUNT = pud_count(KERNEL_IMAGE_SIZE)
> +
> .text
> __HEAD
> .code64
> @@ -396,7 +400,12 @@ NEXT_PAGE(level4_kernel_pgt)
> NEXT_PAGE(level3_kernel_pgt)
> .fill L3_START_KERNEL,8,0
> /* (2^48-(2*1024*1024*1024)-((2^39)*511))/(2^30) = 510 */
> - .quad level2_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE
> + i = 0
> + .rept L3_KERNEL_ENTRY_COUNT
> + .quad level2_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE \
> + + PAGE_SIZE*i
> + i = i + 1
> + .endr
> .quad level2_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
>
> NEXT_PAGE(level2_kernel_pgt)
> --
> 2.13.2.932.g7449e964c-goog
>
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