x86/kexec: Move relocate_kernel to kernel .data section

Now that the copy is executed instead of the original, the relocate_kernel
page can live in the kernel's .text section. This will allow subsequent
commits to actually add real data to it and clean up the code somewhat as
well as making the control page ROX.

Signed-off-by: David Woodhouse <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>
Cc: Baoquan He <[e-mail]>
Cc: Vivek Goyal <[e-mail]>
Cc: Dave Young <[e-mail]>
Cc: Eric Biederman <[e-mail]>
Cc: Ard Biesheuvel <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/x86/include/asm/sections.h

···
 #include <asm-generic/sections.h>
 #include <asm/extable.h>
 
+extern char __relocate_kernel_start[], __relocate_kernel_end[];
 extern char __brk_base[], __brk_limit[];
 extern char __end_rodata_aligned[];
 

arch/x86/kernel/callthunks.c

···
 		return true;
 #endif
 #ifdef CONFIG_KEXEC_CORE
+# ifdef CONFIG_X86_64
+	if (dest >= (void *)__relocate_kernel_start &&
+	    dest < (void *)__relocate_kernel_end)
+		return true;
+# else
 	if (dest >= (void *)relocate_kernel &&
 	    dest < (void*)relocate_kernel + KEXEC_CONTROL_CODE_MAX_SIZE)
 		return true;
+# endif
 #endif
 #ifdef CONFIG_XEN
 	if (dest >= (void *)hypercall_page &&

arch/x86/kernel/machine_kexec_64.c

···
 int machine_kexec_prepare(struct kimage *image)
 {
 	void *control_page = page_address(image->control_code_page);
+	unsigned long reloc_start = (unsigned long)__relocate_kernel_start;
+	unsigned long reloc_end = (unsigned long)__relocate_kernel_end;
 	int result;
 
 	/* Setup the identity mapped 64bit page table */
···
 	if (result)
 		return result;
 
-	__memcpy(control_page, relocate_kernel, KEXEC_CONTROL_CODE_MAX_SIZE);
+	__memcpy(control_page, __relocate_kernel_start, reloc_end - reloc_start);
 
 	set_memory_x((unsigned long)control_page, 1);
 

arch/x86/kernel/relocate_kernel_64.S

···
 #define CP_PA_BACKUP_PAGES_MAP	DATA(0x30)
 #define CP_VA_CONTROL_PAGE	DATA(0x38)
 
-	.text
-	.align PAGE_SIZE
+	.section .text.relocate_kernel,"ax";
 	.code64
-SYM_CODE_START_NOALIGN(relocate_range)
 SYM_CODE_START_NOALIGN(relocate_kernel)
 	UNWIND_HINT_END_OF_STACK
 	ANNOTATE_NOENDBR
···
 	ret
 	int3
 SYM_CODE_END(swap_pages)
-
-	.skip KEXEC_CONTROL_CODE_MAX_SIZE - (. - relocate_kernel), 0xcc
-SYM_CODE_END(relocate_range);

arch/x86/kernel/vmlinux.lds.S

···
 #include <asm/orc_lookup.h>
 #include <asm/cache.h>
 #include <asm/boot.h>
+#include <asm/kexec.h>
 
 #undef i386     /* in case the preprocessor is a 32bit one */
 
···
 #define BSS_DECRYPTED
 
 #endif
+#if defined(CONFIG_X86_64) && defined(CONFIG_KEXEC_CORE)
+#define KEXEC_RELOCATE_KERNEL					\
+	. = ALIGN(0x100);					\
+	__relocate_kernel_start = .;				\
+	*(.text.relocate_kernel);				\
+	__relocate_kernel_end = .;
 
+ASSERT(__relocate_kernel_end - __relocate_kernel_start <= KEXEC_CONTROL_CODE_MAX_SIZE,
+	"relocate_kernel code too large!")
+#else
+#define KEXEC_RELOCATE_KERNEL
+#endif
 PHDRS {
 	text PT_LOAD FLAGS(5);          /* R_E */
 	data PT_LOAD FLAGS(6);          /* RW_ */
···
 
 		DATA_DATA
 		CONSTRUCTORS
+		KEXEC_RELOCATE_KERNEL
 
 		/* rarely changed data like cpu maps */
 		READ_MOSTLY_DATA(INTERNODE_CACHE_BYTES)