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

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Date:   Fri,  4 Nov 2022 19:29:59 +0800
From:   Coiby Xu <coxu@...hat.com>
To:     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>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        "H. Peter Anvin" <hpa@...or.com>
Subject: [RFC v2 4/5] x86/crash: make the page that stores the LUKS volume key inaccessible

This adds an addition layer of protection for the saved copy of LUKS
volume key. Trying to access the saved copy will cause page fault.

Suggested-by: Pingfan Liu <kernelfans@...il.com>
Signed-off-by: Coiby Xu <coxu@...hat.com>
---
 arch/x86/kernel/machine_kexec_64.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 0611fd83858e..f3d51c38a1c9 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -557,9 +557,25 @@ static void kexec_mark_crashkres(bool protect)
 	kexec_mark_range(control, crashk_res.end, protect);
 }
 
+static void kexec_mark_luks_volume_key_inaccessible(void)
+{
+	unsigned long start, end;
+	struct page *page;
+	unsigned int nr_pages;
+
+	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);
+	}
+}
+
 void arch_kexec_protect_crashkres(void)
 {
 	kexec_mark_crashkres(true);
+	kexec_mark_luks_volume_key_inaccessible();
 }
 
 void arch_kexec_unprotect_crashkres(void)
-- 
2.37.3