| Message ID | 20210408131506.17941-1-crecklin@redhat.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v5,1/1] use crc32 instead of md5 for hibernation e820 integrity check | expand |
Hi! > > > > Suspend 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. This integrity check is used only to verify accidental > > > > corruption of the hybernation data > > > > > > It isn't used for that. > > > > > > In fact, it is used to detect differences between the memory map used > > > before hibernation and the one made available by the BIOS during the > > > subsequent resume. And the check is there, because it is generally > > > unsafe to load the hibernation image into memory if the current memory > > > map doesn't match the one used when the image was created. > > > > So what types of "differences" are you trying to detect? If you need to detect > > differences caused by someone who maliciously made changes ("malicious" implies > > they may try to avoid detection), then you need to use a cryptographic hash > > function (or a cryptographic MAC if the hash value isn't stored separately). If > > you only need to detect non-malicious changes (normally these would be called > > "accidental" changes, but sure, it could be changes that are "intentionally" > > made provided that the other side can be trusted to not try to avoid > > detection...) > > That's the case here. md5 is fine for this purpose. crc32 may be too weak. I don't see why this needs changing. Maybe fips should understand that md5 has other uses than crypto? Best regards, Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
On Thu, Apr 29, 2021 at 09:59:44PM +0200, Pavel Machek wrote: > Hi! > > > > > > Suspend 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. This integrity check is used only to verify accidental > > > > > corruption of the hybernation data > > > > > > > > It isn't used for that. > > > > > > > > In fact, it is used to detect differences between the memory map used > > > > before hibernation and the one made available by the BIOS during the > > > > subsequent resume. And the check is there, because it is generally > > > > unsafe to load the hibernation image into memory if the current memory > > > > map doesn't match the one used when the image was created. > > > > > > So what types of "differences" are you trying to detect? If you need to detect > > > differences caused by someone who maliciously made changes ("malicious" implies > > > they may try to avoid detection), then you need to use a cryptographic hash > > > function (or a cryptographic MAC if the hash value isn't stored separately). If > > > you only need to detect non-malicious changes (normally these would be called > > > "accidental" changes, but sure, it could be changes that are "intentionally" > > > made provided that the other side can be trusted to not try to avoid > > > detection...) > > > > That's the case here. > > md5 is fine for this purpose. crc32 may be too weak. I don't see why this needs changing. > > Maybe fips should understand that md5 has other uses than crypto? > > Best regards, > Pavel This would be a good change even if FIPS didn't exist, because either you need a cryptographic digest or you don't. Using MD5 is a big red flag as there isn't really any valid use case for it anymore. We should be working to eliminate all uses of MD5 from the kernel, and likewise for other broken crypto algorithms like RC4. Note that that includes not just upgrading crypto algorithms, but also eliminating cases where crypto was improperly used when it isn't needed. As far as non-cryptographic checksums go, CRC-32 has less than a 1 in 4 billion chance of a collision. People seemed happy with that for this use case. But if a stronger checksum is desired, then CRC-64 or xxHash64 would give a 1 in 2^64 chance of collision instead. - Eric
diff --git a/arch/x86/power/hibernate.c b/arch/x86/power/hibernate.c index cd3914fc9f3d..b56172553275 100644 --- a/arch/x86/power/hibernate.c +++ b/arch/x86/power/hibernate.c @@ -55,31 +55,31 @@ int pfn_is_nosave(unsigned long pfn) } -#define MD5_DIGEST_SIZE 16 +#define CRC32_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]; + u8 e820_digest[CRC32_DIGEST_SIZE]; }; -#if IS_BUILTIN(CONFIG_CRYPTO_MD5) +#if IS_BUILTIN(CONFIG_CRYPTO_CRC32) /** - * get_e820_md5 - calculate md5 according to given e820 table + * get_e820_crc32 - calculate crc32 according to given e820 table * * @table: the e820 table to be calculated - * @buf: the md5 result to be stored to + * @buf: the crc32 result to be stored to */ -static int get_e820_md5(struct e820_table *table, void *buf) +static int get_e820_crc32(struct e820_table *table, void *buf) { struct crypto_shash *tfm; struct shash_desc *desc; int size; int ret = 0; - tfm = crypto_alloc_shash("md5", 0, 0); + tfm = crypto_alloc_shash("crc32", 0, 0); if (IS_ERR(tfm)) return -ENOMEM; @@ -107,24 +107,24 @@ static int get_e820_md5(struct e820_table *table, void *buf) static int hibernation_e820_save(void *buf) { - return get_e820_md5(e820_table_firmware, buf); + return get_e820_crc32(e820_table_firmware, buf); } static bool hibernation_e820_mismatch(void *buf) { int ret; - u8 result[MD5_DIGEST_SIZE]; + u8 result[CRC32_DIGEST_SIZE]; - memset(result, 0, MD5_DIGEST_SIZE); + memset(result, 0, CRC32_DIGEST_SIZE); /* If there is no digest in suspend kernel, let it go. */ - if (!memcmp(result, buf, MD5_DIGEST_SIZE)) + if (!memcmp(result, buf, CRC32_DIGEST_SIZE)) return false; - ret = get_e820_md5(e820_table_firmware, result); + ret = get_e820_crc32(e820_table_firmware, result); if (ret) return true; - return memcmp(result, buf, MD5_DIGEST_SIZE) ? true : false; + return memcmp(result, buf, CRC32_DIGEST_SIZE) ? true : false; } #else static int hibernation_e820_save(void *buf) @@ -134,15 +134,15 @@ static int hibernation_e820_save(void *buf) static bool hibernation_e820_mismatch(void *buf) { - /* If md5 is not builtin for restore kernel, let it go. */ + /* If crc32 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 /** @@ -160,6 +160,9 @@ int arch_hibernation_header_save(void *addr, unsigned int max_size) rdr->jump_address = (unsigned long)restore_registers; rdr->jump_address_phys = __pa_symbol(restore_registers); + /* crc32 digest size is 4 but digest buffer size is 16 so zero it all */ + memset(rdr->e820_digest, 0, CRC32_DIGEST_SIZE); + /* * The restore code fixes up CR3 and CR4 in the following sequence: *
Suspend 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. This integrity check is used only to verify accidental corruption of the hybernation data and is not intended as a cryptographic integrity check. Md5 is overkill in this case and also disabled in FIPS mode because it is known to be broken for cryptographic purposes. Fixes: 62a03defeabd ("PM / hibernate: Verify the consistent of e820 memory map by md5 digest") Tested-by: Dexuan Cui <decui@microsoft.com> Reviewed-by: Dexuan Cui <decui@microsoft.com> 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 arch/x86/power/hibernate.c | 35 +++++++++++++++++++---------------- 1 file changed, 19 insertions(+), 16 deletions(-)