Commit 2beb81fb authored by Eric Biggers's avatar Eric Biggers Committed by Herbert Xu
Browse files

crypto: remove CONFIG_CRYPTO_STATS 

Remove support for the "Crypto usage statistics" feature
(CONFIG_CRYPTO_STATS).  This feature does not appear to have ever been
used, and it is harmful because it significantly reduces performance and
is a large maintenance burden.

Covering each of these points in detail:

1. Feature is not being used

Since these generic crypto statistics are only readable using netlink,
it's fairly straightforward to look for programs that use them.  I'm
unable to find any evidence that any such programs exist.  For example,
Debian Code Search returns no hits except the kernel header and kernel
code itself and translations of the kernel header:
https://codesearch.debian.net/search?q=CRYPTOCFGA_STAT&literal=1&perpkg=1

The patch series that added this feature in 2018
(https://lore.kernel.org/linux-crypto/1537351855-16618-1-git-send-email-clabbe@baylibre.com/)
said "The goal is to have an ifconfig for crypto device."  This doesn't
appear to have happened.

It's not clear that there is real demand for crypto statistics.  Just
because the kernel provides other types of statistics such as I/O and
networking statistics and some people find those useful does not mean
that crypto statistics are useful too.

Further evidence that programs are not using CONFIG_CRYPTO_STATS is that
it was able to be disabled in RHEL and Fedora as a bug fix
(https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/2947).

Even further evidence comes from the fact that there are and have been
bugs in how the stats work, but they were never reported.  For example,
before Linux v6.7 hash stats were double-counted in most cases.

There has also never been any documentation for this feature, so it
might be hard to use even if someone wanted to.

2. CONFIG_CRYPTO_STATS significantly reduces performance

Enabling CONFIG_CRYPTO_STATS significantly reduces the performance of
the crypto API, even if no program ever retrieves the statistics.  This
primarily affects systems with large number of CPUs.  For example,
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2039576

 reported
that Lustre client encryption performance improved from 21.7GB/s to
48.2GB/s by disabling CONFIG_CRYPTO_STATS.

It can be argued that this means that CONFIG_CRYPTO_STATS should be
optimized with per-cpu counters similar to many of the networking
counters.  But no one has done this in 5+ years.  This is consistent
with the fact that the feature appears to be unused, so there seems to
be little interest in improving it as opposed to just disabling it.

It can be argued that because CONFIG_CRYPTO_STATS is off by default,
performance doesn't matter.  But Linux distros tend to error on the side
of enabling options.  The option is enabled in Ubuntu and Arch Linux,
and until recently was enabled in RHEL and Fedora (see above).  So, even
just having the option available is harmful to users.

3. CONFIG_CRYPTO_STATS is a large maintenance burden

There are over 1000 lines of code associated with CONFIG_CRYPTO_STATS,
spread among 32 files.  It significantly complicates much of the
implementation of the crypto API.  After the initial submission, many
fixes and refactorings have consumed effort of multiple people to keep
this feature "working".  We should be spending this effort elsewhere.

Cc: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
Acked-by: default avatarArd Biesheuvel <ardb@kernel.org>
Acked-by: default avatarCorentin Labbe <clabbe@baylibre.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent f66a211e

arch/s390/configs/debug_defconfig

+0 −1
Original line number Diff line number Diff line
@@ -766,7 +766,6 @@ CONFIG_CRYPTO_USER_API_HASH=m 
CONFIG_CRYPTO_USER_API_SKCIPHER=m

CONFIG_CRYPTO_USER_API_RNG=m

CONFIG_CRYPTO_USER_API_AEAD=m

CONFIG_CRYPTO_STATS=y

CONFIG_CRYPTO_CRC32_S390=y

CONFIG_CRYPTO_SHA512_S390=m

CONFIG_CRYPTO_SHA1_S390=m

arch/s390/configs/defconfig

+0 −1
Original line number Diff line number Diff line
@@ -752,7 +752,6 @@ CONFIG_CRYPTO_USER_API_HASH=m 
CONFIG_CRYPTO_USER_API_SKCIPHER=m

CONFIG_CRYPTO_USER_API_RNG=m

CONFIG_CRYPTO_USER_API_AEAD=m

CONFIG_CRYPTO_STATS=y

CONFIG_CRYPTO_CRC32_S390=y

CONFIG_CRYPTO_SHA512_S390=m

CONFIG_CRYPTO_SHA1_S390=m

crypto/Kconfig

+0 −20
Original line number Diff line number Diff line
@@ -1456,26 +1456,6 @@ config CRYPTO_USER_API_ENABLE_OBSOLETE 
	  already been phased out from internal use by the kernel, and are

	  only useful for userspace clients that still rely on them.



config CRYPTO_STATS

	bool "Crypto usage statistics"

	depends on CRYPTO_USER

	help

	  Enable the gathering of crypto stats.



	  Enabling this option reduces the performance of the crypto API.  It

	  should only be enabled when there is actually a use case for it.



	  This collects data sizes, numbers of requests, and numbers

	  of errors processed by:

	  - AEAD ciphers (encrypt, decrypt)

	  - asymmetric key ciphers (encrypt, decrypt, verify, sign)

	  - symmetric key ciphers (encrypt, decrypt)

	  - compression algorithms (compress, decompress)

	  - hash algorithms (hash)

	  - key-agreement protocol primitives (setsecret, generate

	    public key, compute shared secret)

	  - RNG (generate, seed)



endmenu



config CRYPTO_HASH_INFO

crypto/Makefile

+0 −2
Original line number Diff line number Diff line
@@ -69,8 +69,6 @@ cryptomgr-y := algboss.o testmgr.o 


obj-$(CONFIG_CRYPTO_MANAGER2) += cryptomgr.o

obj-$(CONFIG_CRYPTO_USER) += crypto_user.o

crypto_user-y := crypto_user_base.o

crypto_user-$(CONFIG_CRYPTO_STATS) += crypto_user_stat.o

obj-$(CONFIG_CRYPTO_CMAC) += cmac.o

obj-$(CONFIG_CRYPTO_HMAC) += hmac.o

obj-$(CONFIG_CRYPTO_VMAC) += vmac.o

crypto/acompress.c

+3 −44
Original line number Diff line number Diff line
@@ -25,7 +25,7 @@ static const struct crypto_type crypto_acomp_type; 


static inline struct acomp_alg *__crypto_acomp_alg(struct crypto_alg *alg)

{

	return container_of(alg, struct acomp_alg, calg.base);

	return container_of(alg, struct acomp_alg, base);

}



static inline struct acomp_alg *crypto_acomp_alg(struct crypto_acomp *tfm)
@@ -93,32 +93,6 @@ static unsigned int crypto_acomp_extsize(struct crypto_alg *alg) 
	return extsize;

}



static inline int __crypto_acomp_report_stat(struct sk_buff *skb,

					     struct crypto_alg *alg)

{

	struct comp_alg_common *calg = __crypto_comp_alg_common(alg);

	struct crypto_istat_compress *istat = comp_get_stat(calg);

	struct crypto_stat_compress racomp;



	memset(&racomp, 0, sizeof(racomp));



	strscpy(racomp.type, "acomp", sizeof(racomp.type));

	racomp.stat_compress_cnt = atomic64_read(&istat->compress_cnt);

	racomp.stat_compress_tlen = atomic64_read(&istat->compress_tlen);

	racomp.stat_decompress_cnt =  atomic64_read(&istat->decompress_cnt);

	racomp.stat_decompress_tlen = atomic64_read(&istat->decompress_tlen);

	racomp.stat_err_cnt = atomic64_read(&istat->err_cnt);



	return nla_put(skb, CRYPTOCFGA_STAT_ACOMP, sizeof(racomp), &racomp);

}



#ifdef CONFIG_CRYPTO_STATS

int crypto_acomp_report_stat(struct sk_buff *skb, struct crypto_alg *alg)

{

	return __crypto_acomp_report_stat(skb, alg);

}

#endif



static const struct crypto_type crypto_acomp_type = {

	.extsize = crypto_acomp_extsize,

	.init_tfm = crypto_acomp_init_tfm,
@@ -127,9 +101,6 @@ static const struct crypto_type crypto_acomp_type = { 
#endif

#if IS_ENABLED(CONFIG_CRYPTO_USER)

	.report = crypto_acomp_report,

#endif

#ifdef CONFIG_CRYPTO_STATS

	.report_stat = crypto_acomp_report_stat,

#endif

	.maskclear = ~CRYPTO_ALG_TYPE_MASK,

	.maskset = CRYPTO_ALG_TYPE_ACOMPRESS_MASK,
@@ -182,24 +153,12 @@ void acomp_request_free(struct acomp_req *req) 
}

EXPORT_SYMBOL_GPL(acomp_request_free);



void comp_prepare_alg(struct comp_alg_common *alg)

{

	struct crypto_istat_compress *istat = comp_get_stat(alg);

	struct crypto_alg *base = &alg->base;



	base->cra_flags &= ~CRYPTO_ALG_TYPE_MASK;



	if (IS_ENABLED(CONFIG_CRYPTO_STATS))

		memset(istat, 0, sizeof(*istat));

}



int crypto_register_acomp(struct acomp_alg *alg)

{

	struct crypto_alg *base = &alg->calg.base;



	comp_prepare_alg(&alg->calg);

	struct crypto_alg *base = &alg->base;



	base->cra_type = &crypto_acomp_type;

	base->cra_flags &= ~CRYPTO_ALG_TYPE_MASK;

	base->cra_flags |= CRYPTO_ALG_TYPE_ACOMPRESS;



	return crypto_register_alg(base);