[v8,1/1] use crc32 instead of md5 for hibernation e820 integrity check
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Message ID 20210415194646.13387-1-crecklin@redhat.com
State New, archived
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Series
  • [v8,1/1] use crc32 instead of md5 for hibernation e820 integrity check
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Commit Message

Chris von Recklinghausen April 15, 2021, 7:46 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.

This patch changes the integrity check algorithm from md5 to crc32.

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()

 arch/x86/power/hibernate.c | 87 ++++++--------------------------------
 1 file changed, 12 insertions(+), 75 deletions(-)

Comments

Eric Biggers April 15, 2021, 8:09 p.m. UTC | #1
On Thu, Apr 15, 2021 at 03:46:46PM -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.
> 
> This patch changes the integrity check algorithm from md5 to crc32.

The second paragraph is redundant with the first.

>  /**
> - * get_e820_md5 - calculate md5 according to given e820 table
> + * compute_e820_crc32 - calculate md5 according to given e820 table
>   *
>   * @table: the e820 table to be calculated
> - * @buf: the md5 result to be stored to
>   */

This comment still mentions MD5.

Also, this isn't a well-formed kerneldoc comment, since it doesn't document the
return value.

Also, this function is calculating the checksum *of* the table, not calculating
a checksum "according to" it (whatever that means).

Something like this would be good, I think:

/**
 * compute_e820_crc32 - compute the CRC-32 of the given e820 table
 *
 * @table: the e820 table to be checksummed
 *
 * Return: the resulting checksum
 */

Also, please try 'git grep -i md5 arch/x86/kernel/'.  There is still another
reference to MD5 that should be updated, in arch/x86/kernel/e820.c.

- Eric

Patch
diff mbox series

diff --git a/arch/x86/power/hibernate.c b/arch/x86/power/hibernate.c
index cd3914fc9f3d..b358acdc66f4 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 +54,31 @@  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 md5 according to given e820 table
  *
  * @table: the e820 table to be calculated
- * @buf: the md5 result to be stored to
  */
-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);
+	return ~crc32_le(~0, (unsigned char const *)table, size);
 }
 
-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;
-}
-#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 +115,8 @@  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 +137,7 @@  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;
 	}