Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751098AbWEAJwp (ORCPT ); Mon, 1 May 2006 05:52:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751104AbWEAJwp (ORCPT ); Mon, 1 May 2006 05:52:45 -0400 Received: from sv1.valinux.co.jp ([210.128.90.2]:45197 "EHLO sv1.valinux.co.jp") by vger.kernel.org with ESMTP id S1751098AbWEAJwo (ORCPT ); Mon, 1 May 2006 05:52:44 -0400 From: Magnus Damm To: fastboot@lists.osdl.org, linux-kernel@vger.kernel.org Cc: Magnus Damm , ebiederm@xmission.com Message-Id: <20060501095407.16902.78809.sendpatchset@cherry.local> Subject: [PATCH] kexec: Avoid overwriting the current pgd (x86_64) Date: Mon, 1 May 2006 18:52:43 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10035 Lines: 318 kexec: Avoid overwriting the current pgd (x86_64) This patch upgrades the x86_64-specific kexec code to avoid overwriting the current pgd. Overwriting the current pgd is bad when CONFIG_CRASH_DUMP is used to start a secondary kernel that dumps the memory of the previous kernel. The code introduces a new set of page tables called "page_table_a". These tables are used to provide an executable identity mapping without overwriting the current pgd. The already existing page table is renamed to "page_table_b". KEXEC_CONTROL_CODE_SIZE is changed into a single page too. Signed-off-by: Magnus Damm --- The patch has been tested with regular kexec and CONFIG_CRASH_DUMP. Apply on top of 2.6.17-rc3. arch/x86_64/kernel/machine_kexec.c | 138 ++++++++++++++++++++++++---------- arch/x86_64/kernel/relocate_kernel.S | 23 ++++- include/asm-x86_64/kexec.h | 3 include/linux/kexec.h | 7 + 4 files changed, 126 insertions(+), 45 deletions(-) --- 0001/arch/x86_64/kernel/machine_kexec.c +++ work/arch/x86_64/kernel/machine_kexec.c 2006-05-01 13:14:46.000000000 +0900 @@ -2,6 +2,9 @@ * machine_kexec.c - handle transition of Linux booting another kernel * Copyright (C) 2002-2005 Eric Biederman * + * 2006-04-27 Magnus Damm : + * - rewrote identity map code to avoid overwriting current pgd + * * This source code is licensed under the GNU General Public License, * Version 2. See the file COPYING for more details. */ @@ -96,11 +99,15 @@ out: } -static int init_pgtable(struct kimage *image, unsigned long start_pgtable) +static int create_page_table_b(struct kimage *image) { - pgd_t *level4p; - level4p = (pgd_t *)__va(start_pgtable); - return init_level4_page(image, level4p, 0, end_pfn << PAGE_SHIFT); + image->page_table_b = kimage_alloc_control_pages(image, 0); + + if (!image->page_table_b) + return -ENOMEM; + + return init_level4_page(image, page_address(image->page_table_b), + 0, end_pfn << PAGE_SHIFT); } static void set_idt(void *newidt, u16 limit) @@ -147,32 +154,93 @@ static void load_segments(void) typedef NORET_TYPE void (*relocate_new_kernel_t)(unsigned long indirection_page, unsigned long control_code_buffer, unsigned long start_address, - unsigned long pgtable) ATTRIB_NORET; + unsigned long page_table_a, + unsigned long page_table_b) ATTRIB_NORET; const extern unsigned char relocate_new_kernel[]; const extern unsigned long relocate_new_kernel_size; -int machine_kexec_prepare(struct kimage *image) +static int allocate_page_table_a(struct kimage *image) { - unsigned long start_pgtable, control_code_buffer; - int result; + struct page *page; + int k = sizeof(image->page_table_a) / sizeof(image->page_table_a[0]); + + for (; k > 0; k--) { + page = kimage_alloc_control_pages(image, 0); + if (!page) + return -ENOMEM; - /* Calculate the offsets */ - start_pgtable = page_to_pfn(image->control_code_page) << PAGE_SHIFT; - control_code_buffer = start_pgtable + PAGE_SIZE; - - /* Setup the identity mapped 64bit page table */ - result = init_pgtable(image, start_pgtable); - if (result) - return result; - - /* Place the code in the reboot code buffer */ - memcpy(__va(control_code_buffer), relocate_new_kernel, - relocate_new_kernel_size); + clear_page(page_address(page)); + image->page_table_a[k - 1] = page; + } return 0; } +#define _PAGE_KERNEL_EXEC __PAGE_KERNEL_EXEC +#define pa_page(page) __pa_symbol(page_address(page)) /* __pa() miscompiles */ + +static int create_mapping(struct page *root, struct page **pages, + unsigned long va, unsigned long pa) +{ + pgd_t *pgd; + pud_t *pud; + pmd_t *pmd; + pte_t *pte; + int k = 0; + + pgd = (pgd_t *)page_address(root) + pgd_index(va); + if (!pgd_present(*pgd)) + set_pgd(pgd, __pgd(pa_page(pages[k++]) | _KERNPG_TABLE)); + + pud = pud_offset(pgd, va); + if (!pud_present(*pud)) + set_pud(pud, __pud(pa_page(pages[k++]) | _KERNPG_TABLE)); + + pmd = pmd_offset(pud, va); + if (!pmd_present(*pmd)) + set_pmd(pmd, __pmd(pa_page(pages[k++]) | _KERNPG_TABLE)); + + pte = (pte_t *)page_address(pmd_page(*pmd)) + pte_index(va); + set_pte(pte, __pte(pa | _PAGE_KERNEL_EXEC)); + + return k; +} + +int machine_kexec_prepare(struct kimage *image) +{ + void *control_page; + unsigned long pa; + int k; + + k = allocate_page_table_a(image); + if (k) + return k; + + /* fill in control_page with assembly code */ + + control_page = page_address(image->control_code_page); + memcpy(control_page, relocate_new_kernel, relocate_new_kernel_size); + + /* map the control_page at the virtual address of relocate_kernel.S */ + + pa = __pa(control_page); + + k = create_mapping(image->page_table_a[0], + &image->page_table_a[1], + (unsigned long)relocate_new_kernel, pa); + + /* identity map the control_page */ + + create_mapping(image->page_table_a[0], + &image->page_table_a[k + 1], + pa, pa); + + /* create identity mapped page table aka page_table_b */ + + return create_page_table_b(image); +} + void machine_kexec_cleanup(struct kimage *image) { return; @@ -185,34 +253,25 @@ void machine_kexec_cleanup(struct kimage NORET_TYPE void machine_kexec(struct kimage *image) { unsigned long page_list; - unsigned long control_code_buffer; - unsigned long start_pgtable; + unsigned long control_code; + unsigned long page_table_a; + unsigned long page_table_b; relocate_new_kernel_t rnk; /* Interrupts aren't acceptable while we reboot */ local_irq_disable(); - /* Calculate the offsets */ page_list = image->head; - start_pgtable = page_to_pfn(image->control_code_page) << PAGE_SHIFT; - control_code_buffer = start_pgtable + PAGE_SIZE; - - /* Set the low half of the page table to my identity mapped - * page table for kexec. Leave the high half pointing at the - * kernel pages. Don't bother to flush the global pages - * as that will happen when I fully switch to my identity mapped - * page table anyway. - */ - memcpy(__va(read_cr3()), __va(start_pgtable), PAGE_SIZE/2); - __flush_tlb(); - + control_code = __pa(page_address(image->control_code_page)); + page_table_a = __pa(page_address(image->page_table_a[0])); + page_table_b = __pa(page_address(image->page_table_b)); /* The segment registers are funny things, they are * automatically loaded from a table, in memory wherever you * set them to a specific selector, but this table is never - * accessed again unless you set the segment to a different selector. + * accessed again you set the segment to a different selector. * - * The more common model are caches where the behide + * The more common model is are caches where the behide * the scenes work is done, but is also dropped at arbitrary * times. * @@ -225,7 +284,8 @@ NORET_TYPE void machine_kexec(struct kim */ set_gdt(phys_to_virt(0),0); set_idt(phys_to_virt(0),0); + /* now call it */ - rnk = (relocate_new_kernel_t) control_code_buffer; - (*rnk)(page_list, control_code_buffer, image->start, start_pgtable); + rnk = (relocate_new_kernel_t) relocate_new_kernel; + (*rnk)(page_list, control_code, image->start, page_table_a, page_table_b); } --- 0001/arch/x86_64/kernel/relocate_kernel.S +++ work/arch/x86_64/kernel/relocate_kernel.S 2006-05-01 12:32:50.000000000 +0900 @@ -7,6 +7,10 @@ */ #include +#include + +.text +.align (1 << PAGE_SHIFT) /* * Must be relocatable PIC code callable as a C function, that once @@ -18,21 +22,32 @@ relocate_new_kernel: /* %rdi page_list * %rsi reboot_code_buffer * %rdx start address - * %rcx page_table - * %r8 arg5 + * %rcx page_table_a + * %r8 page_table_b * %r9 arg6 */ - + /* zero out flags, and disable interrupts */ pushq $0 popfq + /* switch to page_table_a */ + movq %rcx, %cr3 + /* set a new stack at the bottom of our page... */ lea 4096(%rsi), %rsp /* store the parameters back on the stack */ pushq %rdx /* store the start address */ + /* jump to identity mapped page */ + movq %rsi, %rax + addq $(identity_mapped - relocate_new_kernel), %rax + pushq %rax + ret + +identity_mapped: + /* Set cr0 to a known state: * 31 1 == Paging enabled * 18 0 == Alignment check disabled @@ -69,7 +84,7 @@ relocate_new_kernel: /* Switch to the identity mapped page tables, * and flush the TLB. */ - movq %rcx, %cr3 + movq %r8, %cr3 /* Do the copies */ movq %rdi, %rcx /* Put the page_list in %rcx */ --- 0001/include/asm-x86_64/kexec.h +++ work/include/asm-x86_64/kexec.h 2006-05-01 12:32:50.000000000 +0900 @@ -21,8 +21,7 @@ /* Maximum address we can use for the control pages */ #define KEXEC_CONTROL_MEMORY_LIMIT (0xFFFFFFFFFFUL) -/* Allocate one page for the pdp and the second for the code */ -#define KEXEC_CONTROL_CODE_SIZE (4096UL + 4096UL) +#define KEXEC_CONTROL_CODE_SIZE 4096 /* The native architecture */ #define KEXEC_ARCH KEXEC_ARCH_X86_64 --- 0003/include/linux/kexec.h +++ work/include/linux/kexec.h 2006-05-01 12:32:50.000000000 +0900 @@ -71,6 +71,9 @@ struct kimage { /* page_table_a[] holds enough pages to create a new page table * that maps the control page twice.. + * + * page_table_b points to the root page of a page table which is used + * to provide identity mapping of all ram. */ #if defined(CONFIG_X86_32) && !defined(CONFIG_X86_PAE) @@ -79,6 +82,10 @@ struct kimage { #if defined(CONFIG_X86_32) && defined(CONFIG_X86_PAE) struct page *page_table_a[5]; /* (2 * pte) + (2 * pmd) + pgd */ #endif +#if defined(CONFIG_X86_64) + struct page *page_table_a[7]; /* 2 * (pte + pud + pmd) + pgd */ + struct page *page_table_b; +#endif unsigned long nr_segments; struct kexec_segment segment[KEXEC_SEGMENT_MAX]; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/