On 01/25/2017 08:23 PM, Borislav Petkov wrote:
> On Wed, Jan 25, 2017 at 07:58:39PM +0300, Andrey Ryabinin wrote:
>> On 4.10-rc5
>> # echo 0 > /sys/devices/system/cpu/cpu1/online
>> # echo 1 > /sys/devices/system/cpu/cpu1/online
>>
>> triggers use-after-free (probably caused by 06b8534cb72 "x86/microcode:
>> Rework microcode loading").
>>
>> __load_ucode_intel() accesses initrd which is obviously gone at this point:
>
> Does that help?
Yup.
Tested-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
>
> ---
> diff --git a/arch/x86/kernel/cpu/microcode/core.c
> b/arch/x86/kernel/cpu/microcode/core.c
> index 2af69d27da62..fdbf8d29ffcf 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -248,8 +248,12 @@ struct cpio_data find_microcode_in_initrd(const char
> *path, bool use_pa)
> * possibly relocates the ramdisk. In either case, initrd_start contains
> * the updated address so use that instead.
> */
> - if (!use_pa && initrd_start)
> - start = initrd_start;
> + if (!use_pa) {
> + if (initrd_start)
> + start = initrd_start;
> + else
> + return (struct cpio_data){ NULL, 0, "" };
> + }
>
> return find_cpio_data(path, (void *)start, size, NULL);
> #else /* !CONFIG_BLK_DEV_INITRD */
>
