[PATCH 02/03] kexec: Avoid overwriting the current pgd (V2, i386)
From: Magnus Damm
Date: Wed May 24 2006 - 00:40:45 EST
kexec: Avoid overwriting the current pgd (V2, 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. This updated version of the patch fixes a PAE bug and moves
the segment handling code into the reloacte_kernel.S.
Signed-off-by: Magnus Damm <magnus@xxxxxxxxxxxxx>
---
The patch has been tested with regular kexec and CONFIG_CRASH_DUMP.
Both PAE and non-PAE configurations work well.
Applies on top of 2.6.16 and 2.6.17-rc4.
arch/i386/kernel/machine_kexec.c | 230 ++++++++++++++----------------------
arch/i386/kernel/relocate_kernel.S | 92 ++++++++++++++
include/asm-i386/kexec.h | 12 +
3 files changed, 192 insertions(+), 142 deletions(-)
--- 0001/arch/i386/kernel/machine_kexec.c
+++ work/arch/i386/kernel/machine_kexec.c 2006-05-22 15:57:50.000000000 +0900
@@ -2,6 +2,10 @@
* machine_kexec.c - handle transition of Linux booting another kernel
* Copyright (C) 2002-2005 Eric Biederman <ebiederm@xxxxxxxxxxxx>
*
+ * 2006-05-19 Magnus Damm <damm@xxxxxxxxxxxxx>:
+ * - 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.
*/
@@ -19,123 +23,73 @@
#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)
+typedef asmlinkage NORET_TYPE void (*relocate_new_kernel_t)(
+ unsigned long indirection_page,
+ unsigned long reboot_code_buffer,
+ unsigned long start_address,
+ unsigned long page_table_a,
+ unsigned long has_pae) ATTRIB_NORET;
-#ifndef CONFIG_X86_PAE
-#define LEVEL1_SIZE (1UL << 22UL)
-static u32 pgtable_level1[1024] PAGE_ALIGNED;
+const extern unsigned char relocate_new_kernel[];
+extern void relocate_new_kernel_end(void);
+const extern unsigned int relocate_new_kernel_size;
-static void identity_map_page(unsigned long address)
+static int allocate_page_table_a(struct kimage *image)
{
- unsigned long level1_index, level2_index;
- u32 *pgtable_level2;
-
- /* Find the current page table */
- pgtable_level2 = __va(read_cr3());
+ struct kimage_arch *arch = &image->arch_data;
+ struct page *page;
+ int k = sizeof(arch->page_table_a) / sizeof(arch->page_table_a[0]);
+
+ for (; k > 0; k--) {
+ page = kimage_alloc_control_pages(image, 0);
+ if (!page)
+ return -ENOMEM;
+
+ clear_page(page_address(page));
+ arch->page_table_a[k - 1] = page;
+ }
- /* 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);
+ return 0;
}
-#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;
+/* workaround for include/asm-i386/pgtable-3level.h */
- /* 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);
-}
+#ifdef CONFIG_X86_PAE
+#undef pgd_present
+#define pgd_present(pgd) (pgd_val(pgd) & _PAGE_PRESENT)
+#define _PGD_ATTR _PAGE_PRESENT
+#else
+#define _PGD_ATTR _KERNPG_TABLE
#endif
-static void set_idt(void *newidt, __u16 limit)
-{
- struct Xgt_desc_struct curidt;
-
- /* ia32 supports unaliged loads & stores */
- curidt.size = limit;
- curidt.address = (unsigned long)newidt;
-
- load_idt(&curidt);
-};
+#define pa_page(page) __pa(page_address(page))
-
-static void set_gdt(void *newgdt, __u16 limit)
+static int create_mapping(struct page *root, struct page **pages,
+ unsigned long va, unsigned long pa)
{
- struct Xgt_desc_struct curgdt;
-
- /* ia32 supports unaligned loads & stores */
- curgdt.size = limit;
- curgdt.address = (unsigned long)newgdt;
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *pte;
+ int k = 0;
- load_gdt(&curgdt);
-};
+ pgd = (pgd_t *)page_address(root) + pgd_index(va);
+ if (!pgd_present(*pgd))
+ set_pgd(pgd, __pgd(pa_page(pages[k++]) | _PGD_ATTR));
-static void load_segments(void)
-{
-#define __STR(X) #X
-#define STR(X) __STR(X)
+ pud = pud_offset(pgd, va);
+ if (!pud_present(*pud))
+ set_pud(pud, __pud(pa_page(pages[k++]) | _KERNPG_TABLE));
- __asm__ __volatile__ (
- "\tljmp $"STR(__KERNEL_CS)",$1f\n"
- "\t1:\n"
- "\tmovl $"STR(__KERNEL_DS)",%%eax\n"
- "\tmovl %%eax,%%ds\n"
- "\tmovl %%eax,%%es\n"
- "\tmovl %%eax,%%fs\n"
- "\tmovl %%eax,%%gs\n"
- "\tmovl %%eax,%%ss\n"
- ::: "eax", "memory");
-#undef STR
-#undef __STR
-}
+ pmd = pmd_offset(pud, va);
+ if (!pmd_present(*pmd))
+ set_pmd(pmd, __pmd(pa_page(pages[k++]) | _KERNPG_TABLE));
-typedef asmlinkage NORET_TYPE void (*relocate_new_kernel_t)(
- unsigned long indirection_page,
- unsigned long reboot_code_buffer,
- unsigned long start_address,
- unsigned int has_pae) ATTRIB_NORET;
+ pte = (pte_t *)page_address(pmd_page(*pmd)) + pte_index(va);
+ set_pte(pte, __pte(pa | _PAGE_KERNEL_EXEC));
-const extern unsigned char relocate_new_kernel[];
-extern void relocate_new_kernel_end(void);
-const extern unsigned int relocate_new_kernel_size;
+ return k;
+}
/*
* A architecture hook called to validate the
@@ -147,11 +101,38 @@ const extern unsigned int relocate_new_k
* Do what every setup is needed on image and the
* reboot code buffer to allow us to avoid allocations
* later.
- *
- * Currently nothing.
*/
int machine_kexec_prepare(struct kimage *image)
{
+ void *control_page;
+ unsigned long pa;
+ int k;
+
+ memset(&image->arch_data, 0, sizeof(image->arch_data));
+
+ 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);
+
return 0;
}
@@ -170,45 +151,16 @@ 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);
-
- /* 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 you set the segment to a different selector.
- *
- * The more common model is 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);
+ control_code = __pa(page_address(image->control_code_page));
+ page_table_a = __pa(page_address(image->arch_data.page_table_a[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 2006-05-22 12:55:37.000000000 +0900
@@ -2,12 +2,20 @@
* relocate_kernel.S - put the kernel image in place to boot
* Copyright (C) 2002-2004 Eric Biederman <ebiederm@xxxxxxxxxxxx>
*
+ * 2006-05-19 Magnus Damm <damm@xxxxxxxxxxxxx>:
+ * - moved segment handling code from machine_kexec.c
+ * - gdt tables stolen from arch/i386/boot/setup.S
+ *
* 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
* it starts can not use the previous processes stack.
@@ -18,18 +26,68 @@ 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
+
+ /* setup idt */
+
+ movl %ebp, %eax
+ addl $(idt_48 - relocate_new_kernel), %eax
+ lidtl (%eax)
+
+ /* setup gdt */
+
+ movl %ebp, %eax
+ addl $(gdt - relocate_new_kernel), %eax
+ movl %ebp, %esi
+ addl $((gdt_48 - relocate_new_kernel) + 2), %esi
+ movl %eax, (%esi)
+
+ movl %ebp, %eax
+ addl $(gdt_48 - relocate_new_kernel), %eax
+ lgdtl (%eax)
+
+ /* setup data segment registers */
+
+ mov $(gdt_ds - gdt), %eax
+ mov %eax, %ds
+ mov %eax, %es
+ mov %eax, %fs
+ mov %eax, %gs
+ mov %eax, %ss
+
/* set a new stack at the bottom of our page... */
lea 4096(%ebp), %esp
+ /* load new code segment */
+
+ movl %ebp, %esi
+ xorl %eax, %eax
+ pushl %eax
+ pushl %esi
+ pushl %eax
+
+ movl $(gdt_cs - gdt), %eax
+ pushl %eax
+
+ movl %ebp, %eax
+ addl $(identity_mapped - relocate_new_kernel),%eax
+ pushl %eax
+ iretl
+
+identity_mapped:
+
/* store the parameters back on the stack */
pushl %edx /* store the start address */
-
+
/* Set cr0 to a known state:
* 31 0 == Paging disabled
* 18 0 == Alignment check disabled
@@ -113,6 +171,36 @@ relocate_new_kernel:
xorl %edi, %edi
xorl %ebp, %ebp
ret
+
+ .align 16
+gdt:
+ .fill 1,8,0
+
+gdt_cs:
+ .word 0xFFFF # 4Gb - (0x100000*0x1000 = 4Gb)
+ .word 0 # base address = 0
+ .word 0x9A00 # code read/exec
+ .word 0x00CF # granularity = 4096, 386
+ # (+5th nibble of limit)
+gdt_ds:
+ .word 0xFFFF # 4Gb - (0x100000*0x1000 = 4Gb)
+ .word 0 # base address = 0
+ .word 0x9200 # data read/write
+ .word 0x00CF # granularity = 4096, 386
+ # (+5th nibble of limit)
+gdt_end:
+ .align 4
+
+ .word 0 # alignment byte
+idt_48:
+ .word 0 # idt limit = 0
+ .word 0, 0 # idt base = 0L
+
+ .word 0 # alignment byte
+gdt_48:
+ .word gdt_end - gdt - 1 # gdt limit
+ .word 0, 0 # gdt base (filled in later)
+
relocate_new_kernel_end:
.globl relocate_new_kernel_size
--- 0002/include/asm-i386/kexec.h
+++ work/include/asm-i386/kexec.h 2006-05-22 12:55:38.000000000 +0900
@@ -29,7 +29,17 @@
#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..
+ */
+
+#if defined(CONFIG_X86_PAE)
+ struct page *page_table_a[5]; /* (2 * pte) + (2 * pmd) + pgd */
+#else
+ struct page *page_table_a[3]; /* (2 * pte) + pgd */
+#endif
+};
/* CPU does not save ss and esp on stack if execution is already
* running in kernel mode at the time of NMI occurrence. This code
-
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