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[PATCH] i386: Avoid overwriting the current pgd (V4, i386)
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kexec: Avoid overwriting the current pgd (V4, 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. These tables are used to provide
an executable identity mapping without overwriting the current pgd.

Signed-off-by: Magnus Damm <magnus@valinux.co.jp>
Signed-off-by: Andi Kleen <ak@suse.de>
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Magnus Damm authored and Andi Kleen committed Sep 26, 2006
1 parent 4bfaaef commit 3566561
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Showing 3 changed files with 201 additions and 105 deletions.
117 changes: 27 additions & 90 deletions arch/i386/kernel/machine_kexec.c
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Original file line number Diff line number Diff line change
Expand Up @@ -21,70 +21,13 @@
#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);
}
static u32 kexec_pgd[1024] PAGE_ALIGNED;
#ifdef CONFIG_X86_PAE
static u32 kexec_pmd0[1024] PAGE_ALIGNED;
static u32 kexec_pmd1[1024] PAGE_ALIGNED;
#endif
static u32 kexec_pte0[1024] PAGE_ALIGNED;
static u32 kexec_pte1[1024] PAGE_ALIGNED;

static void set_idt(void *newidt, __u16 limit)
{
Expand Down Expand Up @@ -128,16 +71,6 @@ static void load_segments(void)
#undef __STR
}

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;

extern const unsigned char relocate_new_kernel[];
extern void relocate_new_kernel_end(void);
extern const unsigned int relocate_new_kernel_size;

/*
* A architecture hook called to validate the
* proposed image and prepare the control pages
Expand Down Expand Up @@ -170,25 +103,29 @@ void machine_kexec_cleanup(struct kimage *image)
*/
NORET_TYPE void machine_kexec(struct kimage *image)
{
unsigned long page_list;
unsigned long reboot_code_buffer;

relocate_new_kernel_t rnk;
unsigned long page_list[PAGES_NR];
void *control_page;

/* 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_page = page_address(image->control_code_page);
memcpy(control_page, relocate_kernel, PAGE_SIZE);

page_list[PA_CONTROL_PAGE] = __pa(control_page);
page_list[VA_CONTROL_PAGE] = (unsigned long)relocate_kernel;
page_list[PA_PGD] = __pa(kexec_pgd);
page_list[VA_PGD] = (unsigned long)kexec_pgd;
#ifdef CONFIG_X86_PAE
page_list[PA_PMD_0] = __pa(kexec_pmd0);
page_list[VA_PMD_0] = (unsigned long)kexec_pmd0;
page_list[PA_PMD_1] = __pa(kexec_pmd1);
page_list[VA_PMD_1] = (unsigned long)kexec_pmd1;
#endif
page_list[PA_PTE_0] = __pa(kexec_pte0);
page_list[VA_PTE_0] = (unsigned long)kexec_pte0;
page_list[PA_PTE_1] = __pa(kexec_pte1);
page_list[VA_PTE_1] = (unsigned long)kexec_pte1;

/* The segment registers are funny things, they have both a
* visible and an invisible part. Whenever the visible part is
Expand All @@ -207,8 +144,8 @@ NORET_TYPE void machine_kexec(struct kimage *image)
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);
relocate_kernel((unsigned long)image->head, (unsigned long)page_list,
image->start, cpu_has_pae);
}

/* crashkernel=size@addr specifies the location to reserve for
Expand Down
162 changes: 147 additions & 15 deletions arch/i386/kernel/relocate_kernel.S
View file
Original file line number Diff line number Diff line change
Expand Up @@ -7,28 +7,165 @@
*/

#include <linux/linkage.h>
#include <asm/page.h>
#include <asm/kexec.h>

/*
* Must be relocatable PIC code callable as a C function
*/

#define PTR(x) (x << 2)
#define PAGE_ALIGNED (1 << PAGE_SHIFT)
#define PAGE_ATTR 0x63 /* _PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY */
#define PAE_PGD_ATTR 0x01 /* _PAGE_PRESENT */

.text
.align PAGE_ALIGNED
.globl relocate_kernel
relocate_kernel:
movl 8(%esp), %ebp /* list of pages */

#ifdef CONFIG_X86_PAE
/* map the control page at its virtual address */

movl PTR(VA_PGD)(%ebp), %edi
movl PTR(VA_CONTROL_PAGE)(%ebp), %eax
andl $0xc0000000, %eax
shrl $27, %eax
addl %edi, %eax

movl PTR(PA_PMD_0)(%ebp), %edx
orl $PAE_PGD_ATTR, %edx
movl %edx, (%eax)

movl PTR(VA_PMD_0)(%ebp), %edi
movl PTR(VA_CONTROL_PAGE)(%ebp), %eax
andl $0x3fe00000, %eax
shrl $18, %eax
addl %edi, %eax

movl PTR(PA_PTE_0)(%ebp), %edx
orl $PAGE_ATTR, %edx
movl %edx, (%eax)

movl PTR(VA_PTE_0)(%ebp), %edi
movl PTR(VA_CONTROL_PAGE)(%ebp), %eax
andl $0x001ff000, %eax
shrl $9, %eax
addl %edi, %eax

movl PTR(PA_CONTROL_PAGE)(%ebp), %edx
orl $PAGE_ATTR, %edx
movl %edx, (%eax)

/* identity map the control page at its physical address */

movl PTR(VA_PGD)(%ebp), %edi
movl PTR(PA_CONTROL_PAGE)(%ebp), %eax
andl $0xc0000000, %eax
shrl $27, %eax
addl %edi, %eax

movl PTR(PA_PMD_1)(%ebp), %edx
orl $PAE_PGD_ATTR, %edx
movl %edx, (%eax)

movl PTR(VA_PMD_1)(%ebp), %edi
movl PTR(PA_CONTROL_PAGE)(%ebp), %eax
andl $0x3fe00000, %eax
shrl $18, %eax
addl %edi, %eax

movl PTR(PA_PTE_1)(%ebp), %edx
orl $PAGE_ATTR, %edx
movl %edx, (%eax)

movl PTR(VA_PTE_1)(%ebp), %edi
movl PTR(PA_CONTROL_PAGE)(%ebp), %eax
andl $0x001ff000, %eax
shrl $9, %eax
addl %edi, %eax

movl PTR(PA_CONTROL_PAGE)(%ebp), %edx
orl $PAGE_ATTR, %edx
movl %edx, (%eax)
#else
/* map the control page at its virtual address */

movl PTR(VA_PGD)(%ebp), %edi
movl PTR(VA_CONTROL_PAGE)(%ebp), %eax
andl $0xffc00000, %eax
shrl $20, %eax
addl %edi, %eax

movl PTR(PA_PTE_0)(%ebp), %edx
orl $PAGE_ATTR, %edx
movl %edx, (%eax)

movl PTR(VA_PTE_0)(%ebp), %edi
movl PTR(VA_CONTROL_PAGE)(%ebp), %eax
andl $0x003ff000, %eax
shrl $10, %eax
addl %edi, %eax

movl PTR(PA_CONTROL_PAGE)(%ebp), %edx
orl $PAGE_ATTR, %edx
movl %edx, (%eax)

/* identity map the control page at its physical address */

movl PTR(VA_PGD)(%ebp), %edi
movl PTR(PA_CONTROL_PAGE)(%ebp), %eax
andl $0xffc00000, %eax
shrl $20, %eax
addl %edi, %eax

movl PTR(PA_PTE_1)(%ebp), %edx
orl $PAGE_ATTR, %edx
movl %edx, (%eax)

movl PTR(VA_PTE_1)(%ebp), %edi
movl PTR(PA_CONTROL_PAGE)(%ebp), %eax
andl $0x003ff000, %eax
shrl $10, %eax
addl %edi, %eax

movl PTR(PA_CONTROL_PAGE)(%ebp), %edx
orl $PAGE_ATTR, %edx
movl %edx, (%eax)
#endif

/*
* Must be relocatable PIC code callable as a C function, that once
* it starts can not use the previous processes stack.
*/
.globl relocate_new_kernel
relocate_new_kernel:
/* read the arguments and say goodbye to the stack */
movl 4(%esp), %ebx /* page_list */
movl 8(%esp), %ebp /* reboot_code_buffer */
movl 8(%esp), %ebp /* list of pages */
movl 12(%esp), %edx /* start address */
movl 16(%esp), %ecx /* cpu_has_pae */

/* zero out flags, and disable interrupts */
pushl $0
popfl

/* set a new stack at the bottom of our page... */
lea 4096(%ebp), %esp
/* get physical address of control page now */
/* this is impossible after page table switch */
movl PTR(PA_CONTROL_PAGE)(%ebp), %edi

/* store the parameters back on the stack */
pushl %edx /* store the start address */
/* switch to new set of page tables */
movl PTR(PA_PGD)(%ebp), %eax
movl %eax, %cr3

/* setup a new stack at the end of the physical control page */
lea 4096(%edi), %esp

/* jump to identity mapped page */
movl %edi, %eax
addl $(identity_mapped - relocate_kernel), %eax
pushl %eax
ret

identity_mapped:
/* store the start address on the stack */
pushl %edx

/* Set cr0 to a known state:
* 31 0 == Paging disabled
Expand Down Expand Up @@ -113,8 +250,3 @@ relocate_new_kernel:
xorl %edi, %edi
xorl %ebp, %ebp
ret
relocate_new_kernel_end:

.globl relocate_new_kernel_size
relocate_new_kernel_size:
.long relocate_new_kernel_end - relocate_new_kernel
27 changes: 27 additions & 0 deletions include/asm-i386/kexec.h
View file
Original file line number Diff line number Diff line change
@@ -1,6 +1,26 @@
#ifndef _I386_KEXEC_H
#define _I386_KEXEC_H

#define PA_CONTROL_PAGE 0
#define VA_CONTROL_PAGE 1
#define PA_PGD 2
#define VA_PGD 3
#define PA_PTE_0 4
#define VA_PTE_0 5
#define PA_PTE_1 6
#define VA_PTE_1 7
#ifdef CONFIG_X86_PAE
#define PA_PMD_0 8
#define VA_PMD_0 9
#define PA_PMD_1 10
#define VA_PMD_1 11
#define PAGES_NR 12
#else
#define PAGES_NR 8
#endif

#ifndef __ASSEMBLY__

#include <asm/fixmap.h>
#include <asm/ptrace.h>
#include <asm/string.h>
Expand Down Expand Up @@ -72,5 +92,12 @@ static inline void crash_setup_regs(struct pt_regs *newregs,
newregs->eip = (unsigned long)current_text_addr();
}
}
asmlinkage NORET_TYPE void
relocate_kernel(unsigned long indirection_page,
unsigned long control_page,
unsigned long start_address,
unsigned int has_pae) ATTRIB_NORET;

#endif /* __ASSEMBLY__ */

#endif /* _I386_KEXEC_H */

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