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

Baoquan He
2024-06-07T10:00:58Z

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.

> }
>
> void arch_kexec_unprotect_crashkres(void)
> {
> + kexec_mark_dm_crypt_keys(false);
> kexec_mark_crashkres(false);
> }
> #endif
> --
> 2.45.0
>