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

[Coiby Xu]

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@xxxxxxxxx>
> > Signed-off-by: Coiby Xu <coxu@xxxxxxxxxx>
> > ---
> >  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