Magnus Damm <[email protected]> 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 <[email protected]>
> ---
>
> 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 <[email protected]>
> *
> + * 2006-05-19 Magnus Damm <[email protected]>:
> + * - 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 <[email protected]>
> *
> + * 2006-05-19 Magnus Damm <[email protected]>:
> + * - 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 <linux/linkage.h>
> +#include <asm/page.h>
> +
> +.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==
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>
> --===============37282618571824511==--
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