linux-kernel - Re: [RFC v2 4/5] x86/crash: make the page that stores the LUKS volume key inaccessible

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Message-ID: <1c9a1b86-efef-fa56-4451-ac3348b678bf@intel.com>
Date:   Fri, 4 Nov 2022 07:38:17 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Coiby Xu <coxu@...hat.com>, kexec@...ts.infradead.org
Cc:     Milan Broz <gmazyland@...il.com>,
        Thomas Staudt <tstaudt@...ibm.com>,
        Kairui Song <ryncsn@...il.com>, dm-devel@...hat.com,
        Jan Pazdziora <jpazdziora@...hat.com>,
        Pingfan Liu <kernelfans@...il.com>,
        Baoquan He <bhe@...hat.com>, Dave Young <dyoung@...hat.com>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC v2 4/5] x86/crash: make the page that stores the LUKS volume
 key inaccessible

On 11/4/22 04:29, Coiby Xu wrote:
> +	if (kexec_crash_image->luks_volume_key_addr) {
> +		start = kexec_crash_image->luks_volume_key_addr;
> +		end = start + kexec_crash_image->luks_volume_key_sz - 1;
> +		page = pfn_to_page(start >> PAGE_SHIFT);
> +		nr_pages = (end >> PAGE_SHIFT) - (start >> PAGE_SHIFT) + 1;
> +		set_memory_np((unsigned long)page_address(page), nr_pages);
> +	}

Why does this go pfn -> page -> vaddr?  What good does having the page
do?  Can you just do phys_to_virt() on the start address?  Maybe:

 	start_paddr = kexec_crash_image->luks_volume_key_addr;
 	end_paddr   = start_paddr + kexec_crash_image->luks_volume_key_sz - 1;
 	nr_pages = (PAGE_ALIGN(end_paddr) - PAGE_ALIGN_DOWN(start_paddr))/
PAGE_SIZE;
 	set_memory_np((unsigned long)phys_to_virt(start_paddr), nr_pages);

Also, if you resend this, please just cc the x86 folks on the series.
The other patches and cover letter have desperately needed context
around this.