[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>

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 @@ 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;
-
-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 @@ void machine_kexec_cleanup(struct kimage *image)
  */
 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;
-
-	/* 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_page = page_address(image->control_code_page) + PAGE_SIZE;
+	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;
+	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 @@ NORET_TYPE void machine_kexec(struct kimage *image)
 	 */
 	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

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
+	.globl relocate_kernel
+relocate_kernel:
+	/* %rdi indirection_page
+	 * %rsi page_list
+	 * %rdx start address
+	 */
+
+	/* 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 page_list
-	 * %rsi reboot_code_buffer
+	/* %rdi indirection_page
+	 * %rsi page_list
 	 * %rdx start address
-	 * %rcx page_table
-	 * %r8  arg5
-	 * %r9  arg6
 	 */
 
 	/* 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
+
+	/* get physical address of page table now too */
+	movq	PTR(PA_TABLE_PAGE)(%rsi), %rcx
 
-	/* store the parameters back on the stack */
-	pushq	%rdx /* store the start address */
+	/* 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 @@ relocate_new_kernel:
 	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

include/asm-x86_64/kexec.h

 #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 @@ static inline void crash_setup_regs(struct pt_regs *newregs,
 		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 */