MIPS: relocatable: Provide kaslr_offset() to get the kernel offset

Provide kaslr_offset() to get the kernel offset when KASLR is enabled.
Error may occur before update_kaslr_offset(), so put it at the end of
the offset branch.

Fixes: a307a4ce9e ("MIPS: Loongson64: Add KASLR support")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/page.h

@@ -255,6 +255,12 @@ extern bool __virt_addr_valid(const volatile void *kaddr);
 
 #define VM_DATA_DEFAULT_FLAGS	VM_DATA_FLAGS_TSK_EXEC
 
+extern unsigned long __kaslr_offset;
+static inline unsigned long kaslr_offset(void)
+{
+	return __kaslr_offset;
+}
+
 #include <asm-generic/memory_model.h>
 #include <asm-generic/getorder.h>
 

arch/mips/kernel/relocate.c

@@ -300,6 +300,13 @@ static inline int __init relocation_addr_valid(void *loc_new)
 	return 1;
 }
 
+static inline void __init update_kaslr_offset(unsigned long *addr, long offset)
+{
+	unsigned long *new_addr = (unsigned long *)RELOCATED(addr);
+
+	*new_addr = (unsigned long)offset;
+}
+
 #if defined(CONFIG_USE_OF)
 void __weak *plat_get_fdt(void)
 {
@@ -410,6 +417,9 @@ void *__init relocate_kernel(void)
 
 		/* Return the new kernel's entry point */
 		kernel_entry = RELOCATED(start_kernel);
+
+		/* Error may occur before, so keep it at last */
+		update_kaslr_offset(&__kaslr_offset, offset);
 	}
 out:
 	return kernel_entry;

arch/mips/kernel/setup.c

@@ -84,6 +84,9 @@ static struct resource code_resource = { .name = "Kernel code", };
 static struct resource data_resource = { .name = "Kernel data", };
 static struct resource bss_resource = { .name = "Kernel bss", };
 
+unsigned long __kaslr_offset __ro_after_init;
+EXPORT_SYMBOL(__kaslr_offset);
+
 static void *detect_magic __initdata = detect_memory_region;
 
 #ifdef CONFIG_MIPS_AUTO_PFN_OFFSET