Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964829AbWEYCvf (ORCPT ); Wed, 24 May 2006 22:51:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964834AbWEYCvf (ORCPT ); Wed, 24 May 2006 22:51:35 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:8343 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S964829AbWEYCve (ORCPT ); Wed, 24 May 2006 22:51:34 -0400 To: Magnus Damm Cc: fastboot@lists.osdl.org, linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [Fastboot] [PATCH 03/03] kexec: Avoid overwriting the current pgd (V2, x86_64) References: <20060524044232.14219.68240.sendpatchset@cherry.local> <20060524044247.14219.13579.sendpatchset@cherry.local> From: ebiederm@xmission.com (Eric W. Biederman) Date: Wed, 24 May 2006 20:50:37 -0600 In-Reply-To: <20060524044247.14219.13579.sendpatchset@cherry.local> (Magnus Damm's message of "Wed, 24 May 2006 13:40:46 +0900 (JST)") Message-ID: User-Agent: Gnus/5.1007 (Gnus v5.10.7) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 14473 Lines: 456 Magnus Damm writes: > --===============37282618571824511== > > kexec: Avoid overwriting the current pgd (V2, 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". As I mentioned earlier you don't need two page tables, because it is easy to guarantee that the identity mapping and the virtual mapping will not intersect on x86_64. Until we have as many physical address bits as virtual address bits (which requires page table modifications) it is nonsense to have 2 page tables here. > KEXEC_CONTROL_CODE_SIZE is changed into a single page. This updated version of > the patch also moves the segment handling code into the reloacte_kernel.S. You are doing two things at once here. If it is worth moving the segment handling and idt handling it should be done as a separate patch. > Signed-off-by: Magnus Damm > --- > > The patch has been tested with regular kexec and CONFIG_CRASH_DUMP. > Applies on top of 2.6.16 and 2.6.17-rc4. > > arch/x86_64/kernel/machine_kexec.c | 193 +++++++++++++++++----------------- > arch/x86_64/kernel/relocate_kernel.S | 84 +++++++++++++- > include/asm-x86_64/kexec.h | 15 ++ > 3 files changed, 189 insertions(+), 103 deletions(-) > > --- 0001/arch/x86_64/kernel/machine_kexec.c > +++ work/arch/x86_64/kernel/machine_kexec.c 2006-05-19 12:09:39.000000000 +0900 > @@ -2,6 +2,10 @@ > * machine_kexec.c - handle transition of Linux booting another kernel > * Copyright (C) 2002-2005 Eric Biederman > * > + * 2006-05-19 Magnus Damm : > + * - rewrote identity map code to avoid overwriting current pgd > + * - moved segment handling code into relocate_kernel.S > + * > * This source code is licensed under the GNU General Public License, > * Version 2. See the file COPYING for more details. > */ > @@ -96,81 +100,110 @@ 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); > -} > + struct kimage_arch *arch = &image->arch_data; > > -static void set_idt(void *newidt, u16 limit) > -{ > - struct desc_ptr curidt; > + arch->page_table_b = kimage_alloc_control_pages(image, 0); > > - /* x86-64 supports unaliged loads & stores */ > - curidt.size = limit; > - curidt.address = (unsigned long)newidt; > + if (!arch->page_table_b) > + return -ENOMEM; > > - __asm__ __volatile__ ( > - "lidtq %0\n" > - : : "m" (curidt) > - ); > -}; > + return init_level4_page(image, page_address(arch->page_table_b), > + 0, end_pfn << PAGE_SHIFT); > +} > > +typedef NORET_TYPE void (*relocate_new_kernel_t)(unsigned long > indirection_page, > + unsigned long control_code_buffer, > + unsigned long start_address, > + 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; > > -static void set_gdt(void *newgdt, u16 limit) > +static int allocate_page_table_a(struct kimage *image) > { > - struct desc_ptr curgdt; > + struct kimage_arch *arch = &image->arch_data; > + struct page *page; > + int k = sizeof(arch->page_table_a) / sizeof(arch->page_table_a[0]); > > - /* x86-64 supports unaligned loads & stores */ > - curgdt.size = limit; > - curgdt.address = (unsigned long)newgdt; > + for (; k > 0; k--) { > + page = kimage_alloc_control_pages(image, 0); > + if (!page) > + return -ENOMEM; > > - __asm__ __volatile__ ( > - "lgdtq %0\n" > - : : "m" (curgdt) > - ); > -}; > + clear_page(page_address(page)); > + arch->page_table_a[k - 1] = page; > + } > > -static void load_segments(void) > -{ > - __asm__ __volatile__ ( > - "\tmovl %0,%%ds\n" > - "\tmovl %0,%%es\n" > - "\tmovl %0,%%ss\n" > - "\tmovl %0,%%fs\n" > - "\tmovl %0,%%gs\n" > - : : "a" (__KERNEL_DS) : "memory" > - ); > + return 0; > } > > -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; > +#define _PAGE_KERNEL_EXEC __PAGE_KERNEL_EXEC > +#define pa_page(page) __pa_symbol(page_address(page)) /* __pa() miscompiles */ > > -const extern unsigned char relocate_new_kernel[]; > -const extern unsigned long relocate_new_kernel_size; > +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) > { > - unsigned long start_pgtable, control_code_buffer; > - int result; > + void *control_page; > + unsigned long pa; > + int k; > > - /* 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); > + memset(&image->arch_data, 0, sizeof(image->arch_data)); > > - return 0; > + 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->arch_data.page_table_a[0], > + &image->arch_data.page_table_a[1], > + (unsigned long)relocate_new_kernel, pa); > + > + /* identity map the control_page */ > + > + create_mapping(image->arch_data.page_table_a[0], > + &image->arch_data.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) > @@ -185,47 +218,17 @@ 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; > + control_code = __pa(page_address(image->control_code_page)); > + page_table_a = __pa(page_address(image->arch_data.page_table_a[0])); > + page_table_b = __pa(page_address(image->arch_data.page_table_b)); > > - /* 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(); > - > - > - /* 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. > - * > - * The more common model are caches where the behide > - * the scenes work is done, but is also dropped at arbitrary > - * times. > - * > - * I take advantage of this here by force loading the > - * segments, before I zap the gdt with an invalid value. > - */ > - load_segments(); > - /* The gdt & idt are now invalid. > - * If you want to load them you must set up your own idt & gdt. > - */ > - 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 2006-05-19 12:11:13.000000000 > +0900 > @@ -2,11 +2,18 @@ > * relocate_kernel.S - put the kernel image in place to boot > * Copyright (C) 2002-2005 Eric Biederman > * > + * 2006-05-19 Magnus Damm : > + * - moved segment handling code from machine_kexec.c > + * > * This source code is licensed under the GNU General Public License, > * Version 2. See the file COPYING for more details. > */ > > #include > +#include > + > +.text > +.align (1 << PAGE_SHIFT) > > /* > * Must be relocatable PIC code callable as a C function, that once > @@ -18,21 +25,69 @@ 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 > + > + /* setup idt */ > + > + movq %rsi, %rax > + addq $(idt_48 - relocate_new_kernel), %rax > + lidtq (%rax) > + > + /* setup gdt */ > + > + movq %rsi, %rax > + addq $(gdt - relocate_new_kernel), %rax > + movq %rsi, %r9 > + addq $((gdt_48 - relocate_new_kernel) + 2), %r9 > + movq %rax, (%r9) > + > + movq %rsi, %rax > + addq $(gdt_48 - relocate_new_kernel), %rax > + lgdtq (%rax) > + > + /* setup data segment registers */ > + > + xorl %eax,%eax > + movl %eax, %ds > + movl %eax, %es > + movl %eax, %fs > + movl %eax, %gs > + movl %eax, %ss > + > /* set a new stack at the bottom of our page... */ > lea 4096(%rsi), %rsp > > + /* load new code segment */ > + > + movq %rsp, %rcx > + xorq %rax, %rax > + pushq %rax /* SS */ > + pushq %rcx /* ESP */ > + pushq %rax /* RFLAGS */ > + > + movq $(gdt_code - gdt), %rax > + pushq %rax /* CS */ > + > + movq %rsi, %rax > + addq $(identity_mapped - relocate_new_kernel), %rax > + pushq %rax /* RIP */ > + > + iretq > + > +identity_mapped: > /* store the parameters back on the stack */ > pushq %rdx /* store the start address */ > - > + > /* Set cr0 to a known state: > * 31 1 == Paging enabled > * 18 0 == Alignment check disabled > @@ -69,7 +124,7 @@ 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 */ > @@ -136,6 +191,25 @@ relocate_new_kernel: > xorq %r15, %r15 > > ret > + .align 16 > +gdt: > + .long 0x00000000 /* NULL descriptor */ > + .long 0x00000000 > +gdt_code: > + .long 0x00000000 /* code descriptor */ > + .long 0x00209800 > + > +gdt_end: > + .align 4 > + > +idt_48: > + .word 0 # idt limit = 0 > + .quad 0, 0 # idt base = 0L > + > +gdt_48: > + .word gdt_end - gdt - 1 # gdt limit > + .quad 0, 0 # gdt base (filled in later) > + > relocate_new_kernel_end: > > .globl relocate_new_kernel_size > --- 0002/include/asm-x86_64/kexec.h > +++ work/include/asm-x86_64/kexec.h 2006-05-19 12:07:33.000000000 +0900 > @@ -21,15 +21,24 @@ > /* 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 > > #define MAX_NOTE_BYTES 1024 > > -struct kimage_arch {}; > +struct kimage_arch { > + /* 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. > + */ > + > + struct page *page_table_a[7]; /* 2 * (pte + pud + pmd) + pgd */ > + struct page *page_table_b; > +}; > > /* > * Saving the registers of the cpu on which panic occured in > > --===============37282618571824511== > Content-Type: text/plain; charset="iso-8859-1" > MIME-Version: 1.0 > Content-Transfer-Encoding: quoted-printable > Content-Disposition: inline > > _______________________________________________ > fastboot mailing list > fastboot@lists.osdl.org > https://lists.osdl.org/mailman/listinfo/fastboot > > --===============37282618571824511==-- - 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/