kexec: Avoid overwriting the current pgd (i386)
This patch upgrades the i386-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.
Signed-off-by: Magnus Damm <[email protected]>
---
The patch has been tested with regular kexec and CONFIG_CRASH_DUMP.
Both PAE and non-PAE configurations work well. Apply on top of 2.6.17-rc3.
arch/i386/kernel/machine_kexec.c | 174 +++++++++++++++++++-----------------
arch/i386/kernel/relocate_kernel.S | 19 +++
include/linux/kexec.h | 11 ++
3 files changed, 121 insertions(+), 83 deletions(-)
--- 0001/arch/i386/kernel/machine_kexec.c
+++ work/arch/i386/kernel/machine_kexec.c 2006-05-01 11:38:13.000000000 +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.
*/
@@ -19,72 +22,6 @@
#include <asm/desc.h>
#include <asm/system.h>
-#define PAGE_ALIGNED __attribute__ ((__aligned__(PAGE_SIZE)))
-
-#define L0_ATTR (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY)
-#define L1_ATTR (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY)
-#define L2_ATTR (_PAGE_PRESENT)
-
-#define LEVEL0_SIZE (1UL << 12UL)
-
-#ifndef CONFIG_X86_PAE
-#define LEVEL1_SIZE (1UL << 22UL)
-static u32 pgtable_level1[1024] PAGE_ALIGNED;
-
-static void identity_map_page(unsigned long address)
-{
- unsigned long level1_index, level2_index;
- u32 *pgtable_level2;
-
- /* Find the current page table */
- pgtable_level2 = __va(read_cr3());
-
- /* Find the indexes of the physical address to identity map */
- level1_index = (address % LEVEL1_SIZE)/LEVEL0_SIZE;
- level2_index = address / LEVEL1_SIZE;
-
- /* Identity map the page table entry */
- pgtable_level1[level1_index] = address | L0_ATTR;
- pgtable_level2[level2_index] = __pa(pgtable_level1) | L1_ATTR;
-
- /* Flush the tlb so the new mapping takes effect.
- * Global tlb entries are not flushed but that is not an issue.
- */
- load_cr3(pgtable_level2);
-}
-
-#else
-#define LEVEL1_SIZE (1UL << 21UL)
-#define LEVEL2_SIZE (1UL << 30UL)
-static u64 pgtable_level1[512] PAGE_ALIGNED;
-static u64 pgtable_level2[512] PAGE_ALIGNED;
-
-static void identity_map_page(unsigned long address)
-{
- unsigned long level1_index, level2_index, level3_index;
- u64 *pgtable_level3;
-
- /* Find the current page table */
- pgtable_level3 = __va(read_cr3());
-
- /* Find the indexes of the physical address to identity map */
- level1_index = (address % LEVEL1_SIZE)/LEVEL0_SIZE;
- level2_index = (address % LEVEL2_SIZE)/LEVEL1_SIZE;
- level3_index = address / LEVEL2_SIZE;
-
- /* Identity map the page table entry */
- pgtable_level1[level1_index] = address | L0_ATTR;
- pgtable_level2[level2_index] = __pa(pgtable_level1) | L1_ATTR;
- set_64bit(&pgtable_level3[level3_index],
- __pa(pgtable_level2) | L2_ATTR);
-
- /* Flush the tlb so the new mapping takes effect.
- * Global tlb entries are not flushed but that is not an issue.
- */
- load_cr3(pgtable_level3);
-}
-#endif
-
static void set_idt(void *newidt, __u16 limit)
{
struct Xgt_desc_struct curidt;
@@ -96,7 +33,6 @@ static void set_idt(void *newidt, __u16
load_idt(&curidt);
};
-
static void set_gdt(void *newgdt, __u16 limit)
{
struct Xgt_desc_struct curgdt;
@@ -131,12 +67,66 @@ typedef asmlinkage NORET_TYPE void (*rel
unsigned long indirection_page,
unsigned long reboot_code_buffer,
unsigned long start_address,
- unsigned int has_pae) ATTRIB_NORET;
+ unsigned long page_table_a,
+ unsigned long has_pae) ATTRIB_NORET;
const extern unsigned char relocate_new_kernel[];
extern void relocate_new_kernel_end(void);
const extern unsigned int relocate_new_kernel_size;
+static int allocate_page_table_a(struct kimage *image)
+{
+ 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;
+
+ clear_page(page_address(page));
+ image->page_table_a[k - 1] = page;
+ }
+
+ return 0;
+}
+
+/* workaround for include/asm-i386/pgtable-3level.h */
+
+#ifdef CONFIG_X86_PAE
+#undef pud_present
+#define pud_present(pud) (pud_val(pud) & _PAGE_PRESENT)
+#endif
+
+#define pa_page(page) __pa(page_address(page))
+
+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;
+}
+
/*
* A architecture hook called to validate the
* proposed image and prepare the control pages
@@ -152,6 +142,33 @@ const extern unsigned int relocate_new_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);
+
return 0;
}
@@ -170,24 +187,16 @@ void machine_kexec_cleanup(struct kimage
NORET_TYPE void machine_kexec(struct kimage *image)
{
unsigned long page_list;
- unsigned long reboot_code_buffer;
-
+ unsigned long control_code;
+ unsigned long page_table_a;
relocate_new_kernel_t rnk;
/* Interrupts aren't acceptable while we reboot */
local_irq_disable();
- /* Compute some offsets */
- reboot_code_buffer = page_to_pfn(image->control_code_page)
- << PAGE_SHIFT;
page_list = image->head;
-
- /* Set up an identity mapping for the reboot_code_buffer */
- identity_map_page(reboot_code_buffer);
-
- /* copy it out */
- memcpy((void *)reboot_code_buffer, relocate_new_kernel,
- relocate_new_kernel_size);
+ control_code = __pa(page_address(image->control_code_page));
+ page_table_a = __pa(page_address(image->page_table_a[0]));
/* The segment registers are funny things, they are
* automatically loaded from a table, in memory wherever you
@@ -209,6 +218,7 @@ NORET_TYPE void machine_kexec(struct kim
set_idt(phys_to_virt(0),0);
/* now call it */
- rnk = (relocate_new_kernel_t) reboot_code_buffer;
- (*rnk)(page_list, reboot_code_buffer, image->start, cpu_has_pae);
+ rnk = (relocate_new_kernel_t) relocate_new_kernel;
+ (*rnk)(page_list, control_code, image->start,
+ page_table_a, (unsigned long)cpu_has_pae);
}
--- 0001/arch/i386/kernel/relocate_kernel.S
+++ work/arch/i386/kernel/relocate_kernel.S 2006-05-01 11:13:14.000000000 +0900
@@ -7,7 +7,11 @@
*/
#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
* it starts can not use the previous processes stack.
@@ -18,18 +22,31 @@ relocate_new_kernel:
movl 4(%esp), %ebx /* page_list */
movl 8(%esp), %ebp /* reboot_code_buffer */
movl 12(%esp), %edx /* start address */
- movl 16(%esp), %ecx /* cpu_has_pae */
+ movl 16(%esp), %edi /* page_table_a */
+ movl 20(%esp), %ecx /* cpu_has_pae */
/* zero out flags, and disable interrupts */
pushl $0
popfl
+ /* switch to page_table_a */
+ movl %edi, %eax
+ movl %eax, %cr3
+
/* set a new stack at the bottom of our page... */
lea 4096(%ebp), %esp
/* store the parameters back on the stack */
pushl %edx /* store the start address */
+ /* jump to identity mapped page */
+ movl %ebp, %eax
+ addl $(identity_mapped - relocate_new_kernel), %eax
+ pushl %eax
+ ret
+
+identity_mapped:
+
/* Set cr0 to a known state:
* 31 0 == Paging disabled
* 18 0 == Alignment check disabled
--- 0001/include/linux/kexec.h
+++ work/include/linux/kexec.h 2006-05-01 11:13:14.000000000 +0900
@@ -69,6 +69,17 @@ struct kimage {
unsigned long start;
struct page *control_code_page;
+ /* page_table_a[] holds enough pages to create a new page table
+ * that maps the control page twice..
+ */
+
+#if defined(CONFIG_X86_32) && !defined(CONFIG_X86_PAE)
+ struct page *page_table_a[3]; /* (2 * pte) + pgd */
+#endif
+#if defined(CONFIG_X86_32) && defined(CONFIG_X86_PAE)
+ struct page *page_table_a[5]; /* (2 * pte) + (2 * pmd) + pgd */
+#endif
+
unsigned long nr_segments;
struct kexec_segment segment[KEXEC_SEGMENT_MAX];
-
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