Re: [PATCH] MIPS: relocatable: Provide kaslr_offset() to get the kernel offset

[Jinyang He <hejinyang@loongson.cn>]

On 02/01/2021 08:50 PM, Thomas Bogendoerfer wrote:

> On Wed, Jan 27, 2021 at 12:12:25PM +0800, Jinyang He wrote:
>> Use kimage_vaddr to indicate kernel start address. Provide kaslr_offset()
>> to get the kernel offset when KASLR is enabled. Error may occur before
>> update_kimage_vaddr(), so put it at the end of the offset branch.
>>
>> Fixes: a307a4ce9ecd ("MIPS: Loongson64: Add KASLR support")
>> Reported-by: kernel test robot <lkp@intel.com>
>> Signed-off-by: Jinyang He <hejinyang@loongson.cn>
>> ---
>>   arch/mips/include/asm/page.h |  6 ++++++
>>   arch/mips/kernel/relocate.c  | 12 ++++++++++++
>>   arch/mips/kernel/setup.c     |  3 +++
>>   3 files changed, 21 insertions(+)
>>
>> diff --git a/arch/mips/include/asm/page.h b/arch/mips/include/asm/page.h
>> index 6a77bc4..9429520 100644
>> --- a/arch/mips/include/asm/page.h
>> +++ b/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 kimage_vaddr;
>> +static inline unsigned long kaslr_offset(void)
>> +{
>> +	return kimage_vaddr - VMLINUX_LOAD_ADDRESS;
>> +}
> this breaks for 32bit kernels:
>
> <command-line>:0:22: error: large integer implicitly truncated to unsigned type [-Werror=overflow]
> /local/tbogendoerfer/korg/linux/arch/mips/kernel/setup.c:87:41: note: in expansion of macro ‘VMLINUX_LOAD_ADDRESS’
>   unsigned long kimage_vaddr __initdata = VMLINUX_LOAD_ADDRESS;
>                                           ^~~~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
>

Sorry for not considering the 32bits kernel. Maybe a variable is enough.

Like this,

diff --git a/arch/mips/include/asm/page.h b/arch/mips/include/asm/page.h
index 6a77bc4a6eec..74082e35d57c 100644
--- a/arch/mips/include/asm/page.h
+++ b/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>

diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c
index c643c816cbe0..95abb9c82f00 100644
--- a/arch/mips/kernel/relocate.c
+++ b/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;
diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index 7e1f8e277437..cde234326738 100644
--- a/arch/mips/kernel/setup.c
+++ b/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 __initdata = 0;
+EXPORT_SYMBOL(__kaslr_offset);
+
  static void *detect_magic __initdata = detect_memory_region;

  #ifdef CONFIG_MIPS_AUTO_PFN_OFFSET

I'll send v2 later if no other comment.

Thanks,
Jinyang