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git/hash.h

341 lines
9.3 KiB

#ifndef HASH_H
#define HASH_H
#include "git-compat-util.h"
#include "repository.h"
Makefile + hash.h: remove PPC_SHA1 implementation Remove the PPC_SHA1 implementation added in a6ef3518f9a ([PATCH] PPC assembly implementation of SHA1, 2005-04-22). When this was added Apple consumer hardware used the PPC architecture, and the implementation was intended to improve SHA-1 speed there. Since it was added we've moved to using sha1collisiondetection by default, and anyone wanting hard-rolled non-DC SHA-1 implementation can use OpenSSL's via the OPENSSL_SHA1 knob. The PPC_SHA1 originally originally targeted 32 bit PPC, and later the 64 bit PPC 970 (a.k.a. Apple PowerPC G5). See 926172c5e48 (block-sha1: improve code on large-register-set machines, 2009-08-10) for a reference about the performance on G5 (a comment in block-sha1/sha1.c being removed here). I can't get it to do anything but segfault on both the BE and LE POWER machines in the GCC compile farm[1]. Anyone who's concerned about performance on PPC these days is likely to be using the IBM POWER processors. There have been proposals to entirely remove non-sha1collisiondetection implementations from the tree[2]. I think per [3] that would be a bit overzealous. I.e. there are various set-ups git's speed is going to be more important than the relatively implausible SHA-1 collision attack, or where such attacks are entirely mitigated by other means (e.g. by incoming objects being checked with DC_SHA1). But that really doesn't apply to PPC_SHA1 in particular, which seems to have outlived its usefulness. As this gets rid of the only in-tree *.S assembly file we can remove the small bits of logic from the Makefile needed to build objects from *.S (as opposed to *.c) The code being removed here was also throwing warnings with the "-pedantic" flag, it could have been fixed as 544d93bc3b4 (block-sha1: remove use of obsolete x86 assembly, 2022-03-10) did for block-sha1/*, but as noted above let's remove it instead. 1. https://cfarm.tetaneutral.net/machines/list/ Tested on gcc{110,112,135,203}, a mixture of POWER [789] ppc64 and ppc64le. All segfault in anything needing object hashing (e.g. t/t1007-hash-object.sh) when compiled with PPC_SHA1=Y. 2. https://lore.kernel.org/git/20200223223758.120941-1-mh@glandium.org/ 3. https://lore.kernel.org/git/20200224044732.GK1018190@coredump.intra.peff.net/ Acked-by: brian m. carlson" <sandals@crustytoothpaste.net> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
1 month ago
#if defined(SHA1_APPLE)
#include <CommonCrypto/CommonDigest.h>
#elif defined(SHA1_OPENSSL)
#include <openssl/sha.h>
Makefile: add DC_SHA1 knob This knob lets you use the sha1dc implementation from: https://github.com/cr-marcstevens/sha1collisiondetection which can detect certain types of collision attacks (even when we only see half of the colliding pair). So it mitigates any attack which consists of getting the "good" half of a collision into a trusted repository, and then later replacing it with the "bad" half. The "good" half is rejected by the victim's version of Git (and even if they run an old version of Git, any sha1dc-enabled git will complain loudly if it ever has to interact with the object). The big downside is that it's slower than either the openssl or block-sha1 implementations. Here are some timings based off of linux.git: - compute sha1 over whole packfile sha1dc: 3.580s blk-sha1: 2.046s (-43%) openssl: 1.335s (-62%) - rev-list --all --objects sha1dc: 33.512s blk-sha1: 33.514s (+0.0%) openssl: 33.650s (+0.4%) - git log --no-merges -10000 -p sha1dc: 8.124s blk-sha1: 7.986s (-1.6%) openssl: 8.203s (+0.9%) - index-pack --verify sha1dc: 4m19s blk-sha1: 2m57s (-32%) openssl: 2m19s (-42%) So overall the sha1 computation with collision detection is about 1.75x slower than block-sha1, and 2.7x slower than sha1. But of course most operations do more than just sha1. Normal object access isn't really slowed at all (both the +/- changes there are well within the run-to-run noise); any changes are drowned out by the other work Git is doing. The most-affected operation is `index-pack --verify`, which is essentially just computing the sha1 on every object. This is similar to the `index-pack` invocation that the receiver of a push or fetch would perform. So clearly there's some extra CPU load here. There will also be some latency for the user, though keep in mind that such an operation will generally be network bound (this is about a 1.2GB packfile). Some of that extra CPU is "free" in the sense that we use it while the pack is streaming in anyway. But most of it comes during the delta-resolution phase, after the whole pack has been received. So we can imagine that for this (quite large) push, the user might have to wait an extra 100 seconds over openssl (which is what we use now). If we assume they can push to us at 20Mbit/s, that's 480s for a 1.2GB pack, which is only 20% slower. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
6 years ago
#elif defined(SHA1_DC)
#include "sha1dc_git.h"
#else /* SHA1_BLK */
#include "block-sha1/sha1.h"
#endif
#if defined(SHA256_NETTLE)
#include "sha256/nettle.h"
#elif defined(SHA256_GCRYPT)
#define SHA256_NEEDS_CLONE_HELPER
#include "sha256/gcrypt.h"
#elif defined(SHA256_OPENSSL)
#include <openssl/sha.h>
#else
#include "sha256/block/sha256.h"
#endif
#ifndef platform_SHA_CTX
/*
* platform's underlying implementation of SHA-1; could be OpenSSL,
* blk_SHA, Apple CommonCrypto, etc... Note that the relevant
* SHA-1 header may have already defined platform_SHA_CTX for our
Makefile + hash.h: remove PPC_SHA1 implementation Remove the PPC_SHA1 implementation added in a6ef3518f9a ([PATCH] PPC assembly implementation of SHA1, 2005-04-22). When this was added Apple consumer hardware used the PPC architecture, and the implementation was intended to improve SHA-1 speed there. Since it was added we've moved to using sha1collisiondetection by default, and anyone wanting hard-rolled non-DC SHA-1 implementation can use OpenSSL's via the OPENSSL_SHA1 knob. The PPC_SHA1 originally originally targeted 32 bit PPC, and later the 64 bit PPC 970 (a.k.a. Apple PowerPC G5). See 926172c5e48 (block-sha1: improve code on large-register-set machines, 2009-08-10) for a reference about the performance on G5 (a comment in block-sha1/sha1.c being removed here). I can't get it to do anything but segfault on both the BE and LE POWER machines in the GCC compile farm[1]. Anyone who's concerned about performance on PPC these days is likely to be using the IBM POWER processors. There have been proposals to entirely remove non-sha1collisiondetection implementations from the tree[2]. I think per [3] that would be a bit overzealous. I.e. there are various set-ups git's speed is going to be more important than the relatively implausible SHA-1 collision attack, or where such attacks are entirely mitigated by other means (e.g. by incoming objects being checked with DC_SHA1). But that really doesn't apply to PPC_SHA1 in particular, which seems to have outlived its usefulness. As this gets rid of the only in-tree *.S assembly file we can remove the small bits of logic from the Makefile needed to build objects from *.S (as opposed to *.c) The code being removed here was also throwing warnings with the "-pedantic" flag, it could have been fixed as 544d93bc3b4 (block-sha1: remove use of obsolete x86 assembly, 2022-03-10) did for block-sha1/*, but as noted above let's remove it instead. 1. https://cfarm.tetaneutral.net/machines/list/ Tested on gcc{110,112,135,203}, a mixture of POWER [789] ppc64 and ppc64le. All segfault in anything needing object hashing (e.g. t/t1007-hash-object.sh) when compiled with PPC_SHA1=Y. 2. https://lore.kernel.org/git/20200223223758.120941-1-mh@glandium.org/ 3. https://lore.kernel.org/git/20200224044732.GK1018190@coredump.intra.peff.net/ Acked-by: brian m. carlson" <sandals@crustytoothpaste.net> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
1 month ago
* own implementations like block-sha1, so we list
* the default for OpenSSL compatible SHA-1 implementations here.
*/
#define platform_SHA_CTX SHA_CTX
#define platform_SHA1_Init SHA1_Init
#define platform_SHA1_Update SHA1_Update
#define platform_SHA1_Final SHA1_Final
#endif
#define git_SHA_CTX platform_SHA_CTX
#define git_SHA1_Init platform_SHA1_Init
#define git_SHA1_Update platform_SHA1_Update
#define git_SHA1_Final platform_SHA1_Final
#ifndef platform_SHA256_CTX
#define platform_SHA256_CTX SHA256_CTX
#define platform_SHA256_Init SHA256_Init
#define platform_SHA256_Update SHA256_Update
#define platform_SHA256_Final SHA256_Final
#endif
#define git_SHA256_CTX platform_SHA256_CTX
#define git_SHA256_Init platform_SHA256_Init
#define git_SHA256_Update platform_SHA256_Update
#define git_SHA256_Final platform_SHA256_Final
#ifdef platform_SHA256_Clone
#define git_SHA256_Clone platform_SHA256_Clone
#endif
#ifdef SHA1_MAX_BLOCK_SIZE
#include "compat/sha1-chunked.h"
#undef git_SHA1_Update
#define git_SHA1_Update git_SHA1_Update_Chunked
#endif
static inline void git_SHA1_Clone(git_SHA_CTX *dst, const git_SHA_CTX *src)
{
memcpy(dst, src, sizeof(*dst));
}
#ifndef SHA256_NEEDS_CLONE_HELPER
static inline void git_SHA256_Clone(git_SHA256_CTX *dst, const git_SHA256_CTX *src)
{
memcpy(dst, src, sizeof(*dst));
}
#endif
/*
* Note that these constants are suitable for indexing the hash_algos array and
* comparing against each other, but are otherwise arbitrary, so they should not
* be exposed to the user or serialized to disk. To know whether a
* git_hash_algo struct points to some usable hash function, test the format_id
* field for being non-zero. Use the name field for user-visible situations and
* the format_id field for fixed-length fields on disk.
*/
/* An unknown hash function. */
#define GIT_HASH_UNKNOWN 0
/* SHA-1 */
#define GIT_HASH_SHA1 1
/* SHA-256 */
#define GIT_HASH_SHA256 2
/* Number of algorithms supported (including unknown). */
#define GIT_HASH_NALGOS (GIT_HASH_SHA256 + 1)
/* "sha1", big-endian */
#define GIT_SHA1_FORMAT_ID 0x73686131
/* The length in bytes and in hex digits of an object name (SHA-1 value). */
#define GIT_SHA1_RAWSZ 20
#define GIT_SHA1_HEXSZ (2 * GIT_SHA1_RAWSZ)
/* The block size of SHA-1. */
#define GIT_SHA1_BLKSZ 64
/* "s256", big-endian */
#define GIT_SHA256_FORMAT_ID 0x73323536
/* The length in bytes and in hex digits of an object name (SHA-256 value). */
#define GIT_SHA256_RAWSZ 32
#define GIT_SHA256_HEXSZ (2 * GIT_SHA256_RAWSZ)
/* The block size of SHA-256. */
#define GIT_SHA256_BLKSZ 64
/* The length in byte and in hex digits of the largest possible hash value. */
#define GIT_MAX_RAWSZ GIT_SHA256_RAWSZ
#define GIT_MAX_HEXSZ GIT_SHA256_HEXSZ
/* The largest possible block size for any supported hash. */
#define GIT_MAX_BLKSZ GIT_SHA256_BLKSZ
struct object_id {
unsigned char hash[GIT_MAX_RAWSZ];
oidtree: avoid unaligned access to crit-bit tree The flexible array member "k" of struct cb_node is used to store the key of the crit-bit tree node. It offers no alignment guarantees -- in fact the current struct layout puts it one byte after a 4-byte aligned address, i.e. guaranteed to be misaligned. oidtree uses a struct object_id as cb_node key. Since cf0983213c (hash: add an algo member to struct object_id, 2021-04-26) it requires 4-byte alignment. The mismatch is reported by UndefinedBehaviorSanitizer at runtime like this: hash.h:277:2: runtime error: member access within misaligned address 0x00015000802d for type 'struct object_id', which requires 4 byte alignment 0x00015000802d: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior hash.h:277:2 in We can fix that by: 1. eliminating the alignment requirement of struct object_id, 2. providing the alignment in struct cb_node, or 3. avoiding the issue by only using memcpy to access "k". Currently we only store one of two values in "algo" in struct object_id. We could use a uint8_t for that instead and widen it only once we add support for our twohundredth algorithm or so. That would not only avoid alignment issues, but also reduce the memory requirements for each instance of struct object_id by ca. 9%. Supporting keys with alignment requirements might be useful to spread the use of crit-bit trees. It can be achieved by using a wider type for "k" (e.g. uintmax_t), using different types for the members "byte" and "otherbits" (e.g. uint16_t or uint32_t for each), or by avoiding the use of flexible arrays like khash.h does. This patch implements the third option, though, because it has the least potential for causing side-effects and we're close to the next release. If one of the other options is implemented later as well to get their additional benefits we can get rid of the extra copies introduced here. Reported-by: Andrzej Hunt <andrzej@ahunt.org> Signed-off-by: René Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
1 year ago
int algo; /* XXX requires 4-byte alignment */
};
/* A suitably aligned type for stack allocations of hash contexts. */
union git_hash_ctx {
git_SHA_CTX sha1;
git_SHA256_CTX sha256;
};
typedef union git_hash_ctx git_hash_ctx;
typedef void (*git_hash_init_fn)(git_hash_ctx *ctx);
typedef void (*git_hash_clone_fn)(git_hash_ctx *dst, const git_hash_ctx *src);
typedef void (*git_hash_update_fn)(git_hash_ctx *ctx, const void *in, size_t len);
typedef void (*git_hash_final_fn)(unsigned char *hash, git_hash_ctx *ctx);
typedef void (*git_hash_final_oid_fn)(struct object_id *oid, git_hash_ctx *ctx);
struct git_hash_algo {
/*
* The name of the algorithm, as appears in the config file and in
* messages.
*/
const char *name;
/* A four-byte version identifier, used in pack indices. */
uint32_t format_id;
/* The length of the hash in binary. */
size_t rawsz;
/* The length of the hash in hex characters. */
size_t hexsz;
/* The block size of the hash. */
size_t blksz;
/* The hash initialization function. */
git_hash_init_fn init_fn;
/* The hash context cloning function. */
git_hash_clone_fn clone_fn;
/* The hash update function. */
git_hash_update_fn update_fn;
/* The hash finalization function. */
git_hash_final_fn final_fn;
/* The hash finalization function for object IDs. */
git_hash_final_oid_fn final_oid_fn;
/* The OID of the empty tree. */
const struct object_id *empty_tree;
/* The OID of the empty blob. */
const struct object_id *empty_blob;
/* The all-zeros OID. */
const struct object_id *null_oid;
};
extern const struct git_hash_algo hash_algos[GIT_HASH_NALGOS];
/*
* Return a GIT_HASH_* constant based on the name. Returns GIT_HASH_UNKNOWN if
* the name doesn't match a known algorithm.
*/
int hash_algo_by_name(const char *name);
/* Identical, except based on the format ID. */
int hash_algo_by_id(uint32_t format_id);
/* Identical, except based on the length. */
int hash_algo_by_length(int len);
/* Identical, except for a pointer to struct git_hash_algo. */
static inline int hash_algo_by_ptr(const struct git_hash_algo *p)
{
return p - hash_algos;
}
#define the_hash_algo the_repository->hash_algo
const struct object_id *null_oid(void);
static inline int hashcmp_algop(const unsigned char *sha1, const unsigned char *sha2, const struct git_hash_algo *algop)
{
/*
* Teach the compiler that there are only two possibilities of hash size
* here, so that it can optimize for this case as much as possible.
*/
if (algop->rawsz == GIT_MAX_RAWSZ)
return memcmp(sha1, sha2, GIT_MAX_RAWSZ);
return memcmp(sha1, sha2, GIT_SHA1_RAWSZ);
}
static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
{
return hashcmp_algop(sha1, sha2, the_hash_algo);
}
static inline int oidcmp(const struct object_id *oid1, const struct object_id *oid2)
{
const struct git_hash_algo *algop;
if (!oid1->algo)
algop = the_hash_algo;
else
algop = &hash_algos[oid1->algo];
return hashcmp_algop(oid1->hash, oid2->hash, algop);
}
static inline int hasheq_algop(const unsigned char *sha1, const unsigned char *sha2, const struct git_hash_algo *algop)
{
/*
* We write this here instead of deferring to hashcmp so that the
* compiler can properly inline it and avoid calling memcmp.
*/
if (algop->rawsz == GIT_MAX_RAWSZ)
return !memcmp(sha1, sha2, GIT_MAX_RAWSZ);
return !memcmp(sha1, sha2, GIT_SHA1_RAWSZ);
}
static inline int hasheq(const unsigned char *sha1, const unsigned char *sha2)
{
return hasheq_algop(sha1, sha2, the_hash_algo);
}
static inline int oideq(const struct object_id *oid1, const struct object_id *oid2)
{
const struct git_hash_algo *algop;
if (!oid1->algo)
algop = the_hash_algo;
else
algop = &hash_algos[oid1->algo];
return hasheq_algop(oid1->hash, oid2->hash, algop);
}
static inline int is_null_oid(const struct object_id *oid)
{
return oideq(oid, null_oid());
}
static inline void hashcpy(unsigned char *sha_dst, const unsigned char *sha_src)
{
memcpy(sha_dst, sha_src, the_hash_algo->rawsz);
}
static inline void oidcpy(struct object_id *dst, const struct object_id *src)
{
memcpy(dst->hash, src->hash, GIT_MAX_RAWSZ);
dst->algo = src->algo;
}
/* Like oidcpy() but zero-pads the unused bytes in dst's hash array. */
static inline void oidcpy_with_padding(struct object_id *dst,
const struct object_id *src)
{
size_t hashsz;
if (!src->algo)
hashsz = the_hash_algo->rawsz;
else
hashsz = hash_algos[src->algo].rawsz;
memcpy(dst->hash, src->hash, hashsz);
memset(dst->hash + hashsz, 0, GIT_MAX_RAWSZ - hashsz);
dst->algo = src->algo;
}
static inline struct object_id *oiddup(const struct object_id *src)
{
struct object_id *dst = xmalloc(sizeof(struct object_id));
oidcpy(dst, src);
return dst;
}
static inline void hashclr(unsigned char *hash)
{
memset(hash, 0, the_hash_algo->rawsz);
}
static inline void oidclr(struct object_id *oid)
{
memset(oid->hash, 0, GIT_MAX_RAWSZ);
oid->algo = hash_algo_by_ptr(the_hash_algo);
}
static inline void oidread(struct object_id *oid, const unsigned char *hash)
{
memcpy(oid->hash, hash, the_hash_algo->rawsz);
oid->algo = hash_algo_by_ptr(the_hash_algo);
}
static inline int is_empty_blob_sha1(const unsigned char *sha1)
{
return hasheq(sha1, the_hash_algo->empty_blob->hash);
}
static inline int is_empty_blob_oid(const struct object_id *oid)
{
return oideq(oid, the_hash_algo->empty_blob);
}
static inline int is_empty_tree_sha1(const unsigned char *sha1)
{
return hasheq(sha1, the_hash_algo->empty_tree->hash);
}
static inline int is_empty_tree_oid(const struct object_id *oid)
{
return oideq(oid, the_hash_algo->empty_tree);
}
static inline void oid_set_algo(struct object_id *oid, const struct git_hash_algo *algop)
{
oid->algo = hash_algo_by_ptr(algop);
}
const char *empty_tree_oid_hex(void);
const char *empty_blob_oid_hex(void);
#endif