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

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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


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