Messages in this thread | | | Date | Fri, 22 Jun 2018 10:39:13 +0800 | From | Yu Chen <> | Subject | Re: [PATCH 3/3][RFC] tools: create power/crypto utility |
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Hi Eric, On Wed, Jun 20, 2018 at 10:41:42AM -0700, Eric Biggers wrote: > Hi Chen, > > On Wed, Jun 20, 2018 at 05:40:51PM +0800, Chen Yu wrote: > > crypto_hibernate is a user-space utility to generate > > 512bits AES key and pass it to the kernel via ioctl > > for hibernation encryption.(We can also add the key > > into kernel via keyctl if necessary, but currently > > using ioctl seems to be more straightforward as we > > need both the key and salt transit). > > > > The key derivation is based on a simplified implementation > > of PBKDF2[1] in e2fsprogs - both the key length and the hash > > bytes are the same - 512bits. crypto_hibernate will firstly > > probe the user for passphrase and get salt from kernel, then > > uses them to generate a 512bits AES key based on PBKDF2. Thanks for reviewing this. > > What is a "512bits AES key"? Do you mean AES-256-XTS (which takes a 512-bit > key, which the XTS mode internally splits into two keys)? Yes, it is AES-256-XTS. > Do you allow for > other algorithms, or is it hardcoded to AES-256-XTS? Currently it is hardcoded to AES-256-XTS. It is copied from implementation of PBKDF2 in e2fsprogs, which is hardcoded to useAES-256-XTS for ext4 encryption in the kernel(pbkdf2_sha512() in e2fsprogs) > What if someone wants to > use a different algorithm? > If user wants to use a different algorithm, then I think we need to port the code from openssl, which is the full implementation of PBKDF2 for: https://www.ietf.org/rfc/rfc2898.txt > BTW, it's difficult to review this with only patch 3/3 Cc'ed to me, as there is > no context about the problem you are trying to solve and what your actual > proposed kernel changes are. I suggest Cc'ing linux-crypto on all 3 patches. > Ok, I'll send a refreshed version. > A few more comments below, from a very brief reading of the code: > > [...] > > + > > +#define PBKDF2_ITERATIONS 0xFFFF > > +#define SHA512_BLOCKSIZE 128 > > +#define SHA512_LENGTH 64 > > +#define SALT_BYTES 16 > > +#define SYM_KEY_BYTES SHA512_LENGTH > > +#define TOTAL_USER_INFO_LEN (SALT_BYTES+SYM_KEY_BYTES) > > +#define MAX_PASSPHRASE_SIZE 1024 > > + > > +struct hibernation_crypto_keys { > > + char derived_key[SYM_KEY_BYTES]; > > + char salt[SALT_BYTES]; > > + bool valid; > > +}; > > + > > +struct hibernation_crypto_keys hib_keys; > > + > > +static char *get_key_ptr(void) > > +{ > > + return hib_keys.derived_key; > > +} > > + > > +static char *get_salt_ptr(void) > > +{ > > + return hib_keys.salt; > > +} > [...] > > + > > + > > +#define HIBERNATE_SALT_READ _IOW('C', 3, struct hibernation_crypto_keys) > > +#define HIBERNATE_KEY_WRITE _IOW('C', 4, struct hibernation_crypto_keys) > > Why are the ioctl numbers defined based on the size of 'struct > hibernation_crypto_keys'? It's not a UAPI structure, right? > It's not a UAPI structure, and it is defined both in user space tool and in kernel. Do you mean, I should put the defination of this structure under include/uapi ? > > + > > +static void get_passphrase(char *passphrase, int len) > > +{ > > + char *p; > > + struct termios current_settings; > > + > > + assert(len > 0); > > + disable_echo(¤t_settings); > > + p = fgets(passphrase, len, stdin); > > + tcsetattr(0, TCSANOW, ¤t_settings); > > + printf("\n"); > > + if (!p) { > > + printf("Aborting.\n"); > > + exit(1); > > + } > > + p = strrchr(passphrase, '\n'); > > + if (!p) > > + p = passphrase + len - 1; > > + *p = '\0'; > > +} > > + > > +#define CRYPTO_FILE "/dev/crypto_hibernate" > > + > > +static int write_keys(void) > > +{ > > + int fd; > > + > > + fd = open(CRYPTO_FILE, O_RDWR); > > + if (fd < 0) { > > + printf("Cannot open device file...\n"); > > + return -EINVAL; > > + } > > + ioctl(fd, HIBERNATE_KEY_WRITE, get_key_ptr()); > > + return 0; > > No error checking on the ioctl? > Ok, will add error checking for it. > Also, how is the kernel supposed to know how long the key is, and which > algorithm it's supposed to be used for? I assume it's hardcoded to AES-256-XTS? > What if someone wants to use a different algorithm? > Yes, the length in both user space and kernel are hardcoded to AES-256-XTS. I can add the support for other algorithm, but might need to port from openssl first. > > +} > > + > > +static int read_salt(void) > > +{ > > + int fd; > > + > > + fd = open(CRYPTO_FILE, O_RDWR); > > + if (fd < 0) { > > + printf("Cannot open device file...\n"); > > + return -EINVAL; > > + } > > + ioctl(fd, HIBERNATE_SALT_READ, get_salt_ptr()); > > + return 0; > > +} > > No error checking on the ioctl? > Ok, will add checkings. > > +int main(int argc, char *argv[]) > > +{ > > + int opt, option_index = 0; > > + char in_passphrase[MAX_PASSPHRASE_SIZE]; > > + > > + while ((opt = getopt_long_only(argc, argv, "+p:s:h", > > + NULL, &option_index)) != -1) { > > + switch (opt) { > > + case 'p': > > + { > > + char *p = optarg; > > + > > + if (strlen(p) >= (MAX_PASSPHRASE_SIZE - 1)) { > > + printf("Please provide passphrase less than %d bytes.\n", > > + MAX_PASSPHRASE_SIZE); > > + exit(1); > > + } > > + strcpy(in_passphrase, p); > > I haven't read this super closely, but this really looks like an off-by-one > error. It seems you intended MAX_PASSPHRASE_SIZE to include a null terminator, > so the correct check would be 'strlen(p) >= MAX_PASSPHRASE_SIZE'. > Ah, right, will change it. > > + } > > + break; > > + case 's': > > + { > > + char *p = optarg; > > + > > + if (strlen(p) != (SALT_BYTES - 1)) { > > + printf("Please provide salt with len less than %d bytes.\n", > > + SALT_BYTES); > > + exit(1); > > + } > > + strcpy(get_salt_ptr(), p); > > + } > > + break; > > Salts don't need to be human-readable. How about making the salt binary? So, a > salt specified on the command-line would be hex. > Ok, I will change it to hex form. Best, Yu > Eric
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