diff mbox series

[1/1,v9] use crc32 instead of md5 for hibernation e820 integrity check

Message ID 20210416131655.22112-1-crecklin@redhat.com (mailing list archive)
State Not Applicable
Delegated to: Herbert Xu
Headers show
Series [1/1,v9] use crc32 instead of md5 for hibernation e820 integrity check | expand

Commit Message

Chris von Recklinghausen April 16, 2021, 1:16 p.m. UTC
Hibernation fails on a system in fips mode because md5 is used for the e820
integrity check and is not available. Use crc32 instead.

The check is intended to detect whether the E820 memory map provided
by the firmware after cold boot unexpectedly differs from the one that
was in use when the hibernation image was created. In this case, the
hibernation image cannot be restored, as it may cover memory regions
that are no longer available to the OS.

A non-cryptographic checksum such as CRC-32 is sufficient to detect such
inadvertent deviations.

Fixes: 62a03defeabd ("PM / hibernate: Verify the consistent of e820 memory map
       by md5 digest")

Signed-off-by: Chris von Recklinghausen <crecklin@redhat.com>
---
v1 -> v2
   bump up RESTORE_MAGIC
v2 -> v3
   move embelishment from cover letter to commit comments (no code change)
v3 -> v4
   add note to comments that md5 isn't used for encryption here.
v4 -> v5
   reword comment per Simo's suggestion
v5 -> v6
   use wording from Eric Biggers, use crc32_le instead of crc32 from crypto
	framework (crc32_le is in the core API and removes need for #defines)
v6 -> v7
   reword with input from Eric/Ard/Simo, code changed per Eric's feedback
v7 -> v8
   More feedback per Eric -
   change 'Suspend' to 'Hibernation' in commit comments, rename e820_digest to
   e820_checksum and change it to an unsigned long. rename get_e820_md5 to
   compute_e820_crc32 and have it return the checksum value instead of writing
   it into a user supplied buffer, get rid of hibernation_e820_save in favor of
   calling compute_e820_crc32 directly, likewise, get rid of
   hibernation_e820_mismatch in favor of comparing e820_checksum to the return
   value of compute_e820_crc32()
v8 -> v9
   Make comment for compute_e820_crc32 more kerneldoc friendly. Also update
   comment about the e820 firmware table in arch/x86/kernel/e820.c since it
   also referred to MD5 and hibernation.

 arch/x86/kernel/e820.c     |  4 +-
 arch/x86/power/hibernate.c | 89 ++++++--------------------------------
 2 files changed, 16 insertions(+), 77 deletions(-)

Comments

Eric Biggers April 19, 2021, 10:16 p.m. UTC | #1
On Fri, Apr 16, 2021 at 09:16:55AM -0400, Chris von Recklinghausen wrote:
> Hibernation fails on a system in fips mode because md5 is used for the e820
> integrity check and is not available. Use crc32 instead.

Doesn't the commit title need to be prefixed with something like "x86/power"?

> The check is intended to detect whether the E820 memory map provided
> by the firmware after cold boot unexpectedly differs from the one that
> was in use when the hibernation image was created. In this case, the
> hibernation image cannot be restored, as it may cover memory regions
> that are no longer available to the OS.
> 
> A non-cryptographic checksum such as CRC-32 is sufficient to detect such
> inadvertent deviations.
> 
> Fixes: 62a03defeabd ("PM / hibernate: Verify the consistent of e820 memory map
>        by md5 digest")

The "Fixes" line shouldn't be line-wrapped.

Otherwise this looks fine.  The explanation in the commit message still isn't
great, but it's much better than it was before.

You can add:

	Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric
Dexuan Cui April 19, 2021, 11:33 p.m. UTC | #2
> From: Chris von Recklinghausen <crecklin@redhat.com>
> Sent: Friday, April 16, 2021 6:17 AM
>  ...
> Hibernation fails on a system in fips mode because md5 is used for the e820
> integrity check and is not available. Use crc32 instead.
> 
> The check is intended to detect whether the E820 memory map provided
> by the firmware after cold boot unexpectedly differs from the one that
> was in use when the hibernation image was created. In this case, the
> hibernation image cannot be restored, as it may cover memory regions
> that are no longer available to the OS.
> 
> A non-cryptographic checksum such as CRC-32 is sufficient to detect such
> inadvertent deviations.
> 
> Fixes: 62a03defeabd ("PM / hibernate: Verify the consistent of e820 memory
> map
>        by md5 digest")
> 
> Signed-off-by: Chris von Recklinghausen <crecklin@redhat.com>
> ---

Tested-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>

Thanks Chris and all for the patch!
diff mbox series

Patch

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 22aad412f965..629c4994f165 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -31,8 +31,8 @@ 
  *       - inform the user about the firmware's notion of memory layout
  *         via /sys/firmware/memmap
  *
- *       - the hibernation code uses it to generate a kernel-independent MD5
- *         fingerprint of the physical memory layout of a system.
+ *       - the hibernation code uses it to generate a kernel-independent CRC32
+ *         checksum of the physical memory layout of a system.
  *
  * - 'e820_table_kexec': a slightly modified (by the kernel) firmware version
  *   passed to us by the bootloader - the major difference between
diff --git a/arch/x86/power/hibernate.c b/arch/x86/power/hibernate.c
index cd3914fc9f3d..e94e0050a583 100644
--- a/arch/x86/power/hibernate.c
+++ b/arch/x86/power/hibernate.c
@@ -13,8 +13,8 @@ 
 #include <linux/kdebug.h>
 #include <linux/cpu.h>
 #include <linux/pgtable.h>
-
-#include <crypto/hash.h>
+#include <linux/types.h>
+#include <linux/crc32.h>
 
 #include <asm/e820/api.h>
 #include <asm/init.h>
@@ -54,95 +54,33 @@  int pfn_is_nosave(unsigned long pfn)
 	return pfn >= nosave_begin_pfn && pfn < nosave_end_pfn;
 }
 
-
-#define MD5_DIGEST_SIZE 16
-
 struct restore_data_record {
 	unsigned long jump_address;
 	unsigned long jump_address_phys;
 	unsigned long cr3;
 	unsigned long magic;
-	u8 e820_digest[MD5_DIGEST_SIZE];
+	unsigned long e820_checksum;
 };
 
-#if IS_BUILTIN(CONFIG_CRYPTO_MD5)
 /**
- * get_e820_md5 - calculate md5 according to given e820 table
+ * compute_e820_crc32 - calculate crc32 of a given e820 table
  *
  * @table: the e820 table to be calculated
- * @buf: the md5 result to be stored to
+ *
+ * Return: the resulting checksum
  */
-static int get_e820_md5(struct e820_table *table, void *buf)
+static inline u32 compute_e820_crc32(struct e820_table *table)
 {
-	struct crypto_shash *tfm;
-	struct shash_desc *desc;
-	int size;
-	int ret = 0;
-
-	tfm = crypto_alloc_shash("md5", 0, 0);
-	if (IS_ERR(tfm))
-		return -ENOMEM;
-
-	desc = kmalloc(sizeof(struct shash_desc) + crypto_shash_descsize(tfm),
-		       GFP_KERNEL);
-	if (!desc) {
-		ret = -ENOMEM;
-		goto free_tfm;
-	}
-
-	desc->tfm = tfm;
-
-	size = offsetof(struct e820_table, entries) +
+	int size = offsetof(struct e820_table, entries) +
 		sizeof(struct e820_entry) * table->nr_entries;
 
-	if (crypto_shash_digest(desc, (u8 *)table, size, buf))
-		ret = -EINVAL;
-
-	kfree_sensitive(desc);
-
-free_tfm:
-	crypto_free_shash(tfm);
-	return ret;
-}
-
-static int hibernation_e820_save(void *buf)
-{
-	return get_e820_md5(e820_table_firmware, buf);
-}
-
-static bool hibernation_e820_mismatch(void *buf)
-{
-	int ret;
-	u8 result[MD5_DIGEST_SIZE];
-
-	memset(result, 0, MD5_DIGEST_SIZE);
-	/* If there is no digest in suspend kernel, let it go. */
-	if (!memcmp(result, buf, MD5_DIGEST_SIZE))
-		return false;
-
-	ret = get_e820_md5(e820_table_firmware, result);
-	if (ret)
-		return true;
-
-	return memcmp(result, buf, MD5_DIGEST_SIZE) ? true : false;
-}
-#else
-static int hibernation_e820_save(void *buf)
-{
-	return 0;
-}
-
-static bool hibernation_e820_mismatch(void *buf)
-{
-	/* If md5 is not builtin for restore kernel, let it go. */
-	return false;
+	return ~crc32_le(~0, (unsigned char const *)table, size);
 }
-#endif
 
 #ifdef CONFIG_X86_64
-#define RESTORE_MAGIC	0x23456789ABCDEF01UL
+#define RESTORE_MAGIC	0x23456789ABCDEF02UL
 #else
-#define RESTORE_MAGIC	0x12345678UL
+#define RESTORE_MAGIC	0x12345679UL
 #endif
 
 /**
@@ -179,7 +117,8 @@  int arch_hibernation_header_save(void *addr, unsigned int max_size)
 	 */
 	rdr->cr3 = restore_cr3 & ~CR3_PCID_MASK;
 
-	return hibernation_e820_save(rdr->e820_digest);
+	rdr->e820_checksum = compute_e820_crc32(e820_table_firmware);
+	return 0;
 }
 
 /**
@@ -200,7 +139,7 @@  int arch_hibernation_header_restore(void *addr)
 	jump_address_phys = rdr->jump_address_phys;
 	restore_cr3 = rdr->cr3;
 
-	if (hibernation_e820_mismatch(rdr->e820_digest)) {
+	if (rdr->e820_checksum != compute_e820_crc32(e820_table_firmware)) {
 		pr_crit("Hibernate inconsistent memory map detected!\n");
 		return -ENODEV;
 	}