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 <[EMAIL PROTECTED]>
---
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 <[EMAIL PROTECTED]>
*
+ * 2006-04-27 Magnus Damm <[EMAIL PROTECTED]>:
+ * - 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 <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 +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];
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