Re: [PATCH v4 7/7] x86/crash: make the page that stores the dm crypt keys inaccessible

Coiby Xu
2024-06-07T12:28:47Z

On Fri, Jun 07, 2024 at 06:00:44PM +0800, Baoquan He wrote:
>On 05/23/24 at 01:04pm, Coiby Xu wrote:
>> This adds an addition layer of protection for the saved copy of dm
>> crypt key. Trying to access the saved copy will cause page fault.
>>
>> Suggested-by: Pingfan Liu <kernelfans@gmail.com>
>> Signed-off-by: Coiby Xu <coxu@redhat.com>
>> ---
>> arch/x86/kernel/machine_kexec_64.c | 21 +++++++++++++++++++++
>> 1 file changed, 21 insertions(+)
>>
>> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
>> index b180d8e497c3..fc0a80f4254e 100644
>> --- a/arch/x86/kernel/machine_kexec_64.c
>> +++ b/arch/x86/kernel/machine_kexec_64.c
>> @@ -545,13 +545,34 @@ static void kexec_mark_crashkres(bool protect)
>> kexec_mark_range(control, crashk_res.end, protect);
>> }
>>
>> +static void kexec_mark_dm_crypt_keys(bool protect)
>> +{
>> + unsigned long start_paddr, end_paddr;
>> + unsigned int nr_pages;
>> +
>> + if (kexec_crash_image->dm_crypt_keys_addr) {
>> + start_paddr = kexec_crash_image->dm_crypt_keys_addr;
>> + end_paddr = start_paddr + kexec_crash_image->dm_crypt_keys_sz - 1;
>> + nr_pages = (PAGE_ALIGN(end_paddr) - PAGE_ALIGN_DOWN(start_paddr))/PAGE_SIZE;
>> + if (protect)
>> + set_memory_np((unsigned long)phys_to_virt(start_paddr), nr_pages);
>> + else
>> + __set_memory_prot(
>> + (unsigned long)phys_to_virt(start_paddr),
>> + nr_pages,
>> + __pgprot(_PAGE_PRESENT | _PAGE_NX | _PAGE_RW));
>> + }
>> +}
>> +
>> void arch_kexec_protect_crashkres(void)
>> {
>> kexec_mark_crashkres(true);
>> + kexec_mark_dm_crypt_keys(true);
>
>Isn't crashkernel region covering crypt keys' storing region? Do we need
>mark it again specifically? Not sure if I miss anything.

kexec_mark_crashkres only makes the page read-only whereas
kexec_mark_dm_crypt_keys makes the memory inaccessible. I've added a
comment for this function in v5 and hopefully no one will be confused by
it.

--
Best regards,
Coiby