[PATCH] Avoid overwriting the current pgd (V4, x86_64)
kexec: Avoid overwriting the current pgd (V4, 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. 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>
diff --git a/arch/x86_64/kernel/machine_kexec.c b/arch/x86_64/kernel/machine_kexec.c
index 2e94c07..0497e3b 100644
--- a/arch/x86_64/kernel/machine_kexec.c
+++ b/arch/x86_64/kernel/machine_kexec.c
@@ -15,6 +15,15 @@
#include <asm/mmu_context.h>
#include <asm/io.h>
+#define PAGE_ALIGNED __attribute__ ((__aligned__(PAGE_SIZE)))
+static u64 kexec_pgd[512] PAGE_ALIGNED;
+static u64 kexec_pud0[512] PAGE_ALIGNED;
+static u64 kexec_pmd0[512] PAGE_ALIGNED;
+static u64 kexec_pte0[512] PAGE_ALIGNED;
+static u64 kexec_pud1[512] PAGE_ALIGNED;
+static u64 kexec_pmd1[512] PAGE_ALIGNED;
+static u64 kexec_pte1[512] PAGE_ALIGNED;
+
static void init_level2_page(pmd_t *level2p, unsigned long addr)
{
unsigned long end_addr;
@@ -144,32 +153,19 @@
);
}
-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;
-
-extern const unsigned char relocate_new_kernel[];
-extern const unsigned long relocate_new_kernel_size;
-
int machine_kexec_prepare(struct kimage *image)
{
- unsigned long start_pgtable, control_code_buffer;
+ unsigned long start_pgtable;
int result;
/* 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);
-
return 0;
}
@@ -184,28 +180,34 @@
*/
NORET_TYPE void machine_kexec(struct kimage *image)
{
- unsigned long page_list;
- unsigned long control_code_buffer;
- unsigned long start_pgtable;
- relocate_new_kernel_t rnk;
+ unsigned long page_list[PAGES_NR];
+ void *control_page;
/* 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_page = page_address(image->control_code_page) + PAGE_SIZE;
+ memcpy(control_page, relocate_kernel, 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();
+ 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;
+ page_list[PA_PUD_0] = __pa(kexec_pud0);
+ page_list[VA_PUD_0] = (unsigned long)kexec_pud0;
+ page_list[PA_PMD_0] = __pa(kexec_pmd0);
+ page_list[VA_PMD_0] = (unsigned long)kexec_pmd0;
+ page_list[PA_PTE_0] = __pa(kexec_pte0);
+ page_list[VA_PTE_0] = (unsigned long)kexec_pte0;
+ page_list[PA_PUD_1] = __pa(kexec_pud1);
+ page_list[VA_PUD_1] = (unsigned long)kexec_pud1;
+ page_list[PA_PMD_1] = __pa(kexec_pmd1);
+ page_list[VA_PMD_1] = (unsigned long)kexec_pmd1;
+ page_list[PA_PTE_1] = __pa(kexec_pte1);
+ page_list[VA_PTE_1] = (unsigned long)kexec_pte1;
+ page_list[PA_TABLE_PAGE] =
+ (unsigned long)__pa(page_address(image->control_code_page));
/* The segment registers are funny things, they have both a
* visible and an invisible part. Whenever the visible part is
@@ -222,9 +224,10 @@
*/
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);
+ relocate_kernel((unsigned long)image->head, (unsigned long)page_list,
+ image->start);
}
/* crashkernel=size@addr specifies the location to reserve for
diff --git a/arch/x86_64/kernel/relocate_kernel.S b/arch/x86_64/kernel/relocate_kernel.S
index d24fa9b..14e9587 100644
--- a/arch/x86_64/kernel/relocate_kernel.S
+++ b/arch/x86_64/kernel/relocate_kernel.S
@@ -7,31 +7,169 @@
*/
#include <linux/linkage.h>
+#include <asm/page.h>
+#include <asm/kexec.h>
- /*
- * 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
+/*
+ * Must be relocatable PIC code callable as a C function
+ */
+
+#define PTR(x) (x << 3)
+#define PAGE_ALIGNED (1 << PAGE_SHIFT)
+#define PAGE_ATTR 0x63 /* _PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY */
+
+ .text
+ .align PAGE_ALIGNED
.code64
-relocate_new_kernel:
- /* %rdi page_list
- * %rsi reboot_code_buffer
+ .globl relocate_kernel
+relocate_kernel:
+ /* %rdi indirection_page
+ * %rsi page_list
* %rdx start address
- * %rcx page_table
- * %r8 arg5
- * %r9 arg6
+ */
+
+ /* map the control page at its virtual address */
+
+ movq $0x0000ff8000000000, %r10 /* mask */
+ mov $(39 - 3), %cl /* bits to shift */
+ movq PTR(VA_CONTROL_PAGE)(%rsi), %r11 /* address to map */
+
+ movq %r11, %r9
+ andq %r10, %r9
+ shrq %cl, %r9
+
+ movq PTR(VA_PGD)(%rsi), %r8
+ addq %r8, %r9
+ movq PTR(PA_PUD_0)(%rsi), %r8
+ orq $PAGE_ATTR, %r8
+ movq %r8, (%r9)
+
+ shrq $9, %r10
+ sub $9, %cl
+
+ movq %r11, %r9
+ andq %r10, %r9
+ shrq %cl, %r9
+
+ movq PTR(VA_PUD_0)(%rsi), %r8
+ addq %r8, %r9
+ movq PTR(PA_PMD_0)(%rsi), %r8
+ orq $PAGE_ATTR, %r8
+ movq %r8, (%r9)
+
+ shrq $9, %r10
+ sub $9, %cl
+
+ movq %r11, %r9
+ andq %r10, %r9
+ shrq %cl, %r9
+
+ movq PTR(VA_PMD_0)(%rsi), %r8
+ addq %r8, %r9
+ movq PTR(PA_PTE_0)(%rsi), %r8
+ orq $PAGE_ATTR, %r8
+ movq %r8, (%r9)
+
+ shrq $9, %r10
+ sub $9, %cl
+
+ movq %r11, %r9
+ andq %r10, %r9
+ shrq %cl, %r9
+
+ movq PTR(VA_PTE_0)(%rsi), %r8
+ addq %r8, %r9
+ movq PTR(PA_CONTROL_PAGE)(%rsi), %r8
+ orq $PAGE_ATTR, %r8
+ movq %r8, (%r9)
+
+ /* identity map the control page at its physical address */
+
+ movq $0x0000ff8000000000, %r10 /* mask */
+ mov $(39 - 3), %cl /* bits to shift */
+ movq PTR(PA_CONTROL_PAGE)(%rsi), %r11 /* address to map */
+
+ movq %r11, %r9
+ andq %r10, %r9
+ shrq %cl, %r9
+
+ movq PTR(VA_PGD)(%rsi), %r8
+ addq %r8, %r9
+ movq PTR(PA_PUD_1)(%rsi), %r8
+ orq $PAGE_ATTR, %r8
+ movq %r8, (%r9)
+
+ shrq $9, %r10
+ sub $9, %cl
+
+ movq %r11, %r9
+ andq %r10, %r9
+ shrq %cl, %r9
+
+ movq PTR(VA_PUD_1)(%rsi), %r8
+ addq %r8, %r9
+ movq PTR(PA_PMD_1)(%rsi), %r8
+ orq $PAGE_ATTR, %r8
+ movq %r8, (%r9)
+
+ shrq $9, %r10
+ sub $9, %cl
+
+ movq %r11, %r9
+ andq %r10, %r9
+ shrq %cl, %r9
+
+ movq PTR(VA_PMD_1)(%rsi), %r8
+ addq %r8, %r9
+ movq PTR(PA_PTE_1)(%rsi), %r8
+ orq $PAGE_ATTR, %r8
+ movq %r8, (%r9)
+
+ shrq $9, %r10
+ sub $9, %cl
+
+ movq %r11, %r9
+ andq %r10, %r9
+ shrq %cl, %r9
+
+ movq PTR(VA_PTE_1)(%rsi), %r8
+ addq %r8, %r9
+ movq PTR(PA_CONTROL_PAGE)(%rsi), %r8
+ orq $PAGE_ATTR, %r8
+ movq %r8, (%r9)
+
+relocate_new_kernel:
+ /* %rdi indirection_page
+ * %rsi page_list
+ * %rdx start address
*/
/* zero out flags, and disable interrupts */
pushq $0
popfq
- /* set a new stack at the bottom of our page... */
- lea 4096(%rsi), %rsp
+ /* get physical address of control page now */
+ /* this is impossible after page table switch */
+ movq PTR(PA_CONTROL_PAGE)(%rsi), %r8
- /* store the parameters back on the stack */
- pushq %rdx /* store the start address */
+ /* get physical address of page table now too */
+ movq PTR(PA_TABLE_PAGE)(%rsi), %rcx
+
+ /* switch to new set of page tables */
+ movq PTR(PA_PGD)(%rsi), %r9
+ movq %r9, %cr3
+
+ /* setup a new stack at the end of the physical control page */
+ lea 4096(%r8), %rsp
+
+ /* jump to identity mapped page */
+ addq $(identity_mapped - relocate_kernel), %r8
+ pushq %r8
+ ret
+
+identity_mapped:
+ /* store the start address on the stack */
+ pushq %rdx
/* Set cr0 to a known state:
* 31 1 == Paging enabled
@@ -136,8 +274,3 @@
xorq %r15, %r15
ret
-relocate_new_kernel_end:
-
- .globl relocate_new_kernel_size
-relocate_new_kernel_size:
- .quad relocate_new_kernel_end - relocate_new_kernel
diff --git a/include/asm-x86_64/kexec.h b/include/asm-x86_64/kexec.h
index c564bae..5fab957 100644
--- a/include/asm-x86_64/kexec.h
+++ b/include/asm-x86_64/kexec.h
@@ -1,6 +1,27 @@
#ifndef _X86_64_KEXEC_H
#define _X86_64_KEXEC_H
+#define PA_CONTROL_PAGE 0
+#define VA_CONTROL_PAGE 1
+#define PA_PGD 2
+#define VA_PGD 3
+#define PA_PUD_0 4
+#define VA_PUD_0 5
+#define PA_PMD_0 6
+#define VA_PMD_0 7
+#define PA_PTE_0 8
+#define VA_PTE_0 9
+#define PA_PUD_1 10
+#define VA_PUD_1 11
+#define PA_PMD_1 12
+#define VA_PMD_1 13
+#define PA_PTE_1 14
+#define VA_PTE_1 15
+#define PA_TABLE_PAGE 16
+#define PAGES_NR 17
+
+#ifndef __ASSEMBLY__
+
#include <linux/string.h>
#include <asm/page.h>
@@ -64,4 +85,12 @@
newregs->rip = (unsigned long)current_text_addr();
}
}
+
+NORET_TYPE void
+relocate_kernel(unsigned long indirection_page,
+ unsigned long page_list,
+ unsigned long start_address) ATTRIB_NORET;
+
+#endif /* __ASSEMBLY__ */
+
#endif /* _X86_64_KEXEC_H */