linux-kernel - [PATCH v2 5/5] x86/crash: make the page that stores the dm crypt key inaccessible

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Date: Wed, 10 Jan 2024 15:15:20 +0800
From: Coiby Xu <coxu@...hat.com>
To: kexec@...ts.infradead.org
Cc: Ondrej Kozina <okozina@...hat.com>,
	Milan Broz <gmazyland@...il.com>,
	Thomas Staudt <tstaudt@...ibm.com>,
	Daniel P . Berrangé <berrange@...hat.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,
	x86@...nel.org,
	Dave Hansen <dave.hansen@...el.com>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH v2 5/5] x86/crash: make the page that stores the dm crypt key inaccessible

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@...il.com>
Signed-off-by: Coiby Xu <coxu@...hat.com>
---
 arch/x86/kernel/machine_kexec_64.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 1a3e2c05a8a5..c9c814b934b8 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -546,14 +546,32 @@ static void kexec_mark_crashkres(bool protect)
 	kexec_mark_range(control, crashk_res.end, protect);
 }
 
+static void kexec_mark_dm_crypt_key(bool protect)
+{
+	unsigned long start_paddr, end_paddr;
+	unsigned int nr_pages;
+
+	if (kexec_crash_image->dm_crypt_key_addr) {
+		start_paddr = kexec_crash_image->dm_crypt_key_addr;
+		end_paddr = start_paddr + kexec_crash_image->dm_crypt_key_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_rw((unsigned long)phys_to_virt(start_paddr), nr_pages);
+	}
+}
+
 void arch_kexec_protect_crashkres(void)
 {
 	kexec_mark_crashkres(true);
+	kexec_mark_dm_crypt_key(true);
 }
 
 void arch_kexec_unprotect_crashkres(void)
 {
 	kexec_mark_crashkres(false);
+	kexec_mark_dm_crypt_key(false);
 }
 
 /*
-- 
2.43.0