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[104.178.186.189]) by smtp.gmail.com with ESMTPSA id 00721157ae682-6d78d1e6901sm16700867b3.7.2024.09.05.08.12.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Sep 2024 08:12:13 -0700 (PDT) Date: Thu, 5 Sep 2024 11:12:12 -0400 From: Taylor Blau To: git@vger.kernel.org Cc: Jeff King , "brian m. carlson" , Elijah Newren , Patrick Steinhardt , Junio C Hamano Subject: [PATCH v2 2/4] hash.h: scaffolding for _fast hashing variants Message-ID: <3b5f21e4a620b0afd706ec3a3fbb71918f96198f.1725549065.git.me@ttaylorr.com> References: Precedence: bulk X-Mailing-List: git@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Git's default SHA-1 implementation is collision-detecting, which hardens us against known SHA-1 attacks against Git objects. This makes Git object writes safer at the expense of some speed when hashing through the collision-detecting implementation, which is slower than non-collision detecting alternatives. Prepare for loading a separate "fast" SHA-1 implementation that can be used for non-cryptographic purposes, like computing the checksum of files that use the hashwrite() API. This commit does not actually introduce any new compile-time knobs to control which implementation is used as the fast SHA-1 variant, but does add scaffolding so that the "git_hash_algo" structure has five new function pointers which are "fast" variants of the five existing hashing-related function pointers: - git_hash_init_fn fast_init_fn - git_hash_clone_fn fast_clone_fn - git_hash_update_fn fast_update_fn - git_hash_final_fn fast_final_fn - git_hash_final_oid_fn fast_final_oid_fn The following commit will introduce compile-time knobs to specify which SHA-1 implementation is used for non-cryptographic uses. Signed-off-by: Taylor Blau --- hash.h | 42 ++++++++++++++++++++++++++++++++++++++++++ object-file.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 84 insertions(+) diff --git a/hash.h b/hash.h index 72ffbc862e5..5e5b8205b58 100644 --- a/hash.h +++ b/hash.h @@ -44,14 +44,32 @@ #define platform_SHA1_Final SHA1_Final #endif +#ifndef platform_SHA_CTX_fast +# define platform_SHA_CTX_fast platform_SHA_CTX +# define platform_SHA1_Init_fast platform_SHA1_Init +# define platform_SHA1_Update_fast platform_SHA1_Update +# define platform_SHA1_Final_fast platform_SHA1_Final +# ifdef platform_SHA1_Clone +# define platform_SHA1_Clone_fast platform_SHA1_Clone +# endif +#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 +#define git_SHA_CTX_fast platform_SHA_CTX_fast +#define git_SHA1_Init_fast platform_SHA1_Init_fast +#define git_SHA1_Update_fast platform_SHA1_Update_fast +#define git_SHA1_Final_fast platform_SHA1_Final_fast + #ifdef platform_SHA1_Clone #define git_SHA1_Clone platform_SHA1_Clone #endif +#ifdef platform_SHA1_Clone_fast +# define git_SHA1_Clone_fast platform_SHA1_Clone_fast +#endif #ifndef platform_SHA256_CTX #define platform_SHA256_CTX SHA256_CTX @@ -81,6 +99,13 @@ static inline void git_SHA1_Clone(git_SHA_CTX *dst, const git_SHA_CTX *src) memcpy(dst, src, sizeof(*dst)); } #endif +#ifndef SHA1_NEEDS_CLONE_HELPER_FAST +static inline void git_SHA1_Clone_fast(git_SHA_CTX_fast *dst, + const git_SHA_CTX_fast *src) +{ + memcpy(dst, src, sizeof(*dst)); +} +#endif #ifndef SHA256_NEEDS_CLONE_HELPER static inline void git_SHA256_Clone(git_SHA256_CTX *dst, const git_SHA256_CTX *src) @@ -178,6 +203,8 @@ enum get_oid_result { /* A suitably aligned type for stack allocations of hash contexts. */ union git_hash_ctx { git_SHA_CTX sha1; + git_SHA_CTX_fast sha1_fast; + git_SHA256_CTX sha256; }; typedef union git_hash_ctx git_hash_ctx; @@ -222,6 +249,21 @@ struct git_hash_algo { /* The hash finalization function for object IDs. */ git_hash_final_oid_fn final_oid_fn; + /* The fast / non-cryptographic hash initialization function. */ + git_hash_init_fn fast_init_fn; + + /* The fast / non-cryptographic hash context cloning function. */ + git_hash_clone_fn fast_clone_fn; + + /* The fast / non-cryptographic hash update function. */ + git_hash_update_fn fast_update_fn; + + /* The fast / non-cryptographic hash finalization function. */ + git_hash_final_fn fast_final_fn; + + /* The fast / non-cryptographic hash finalization function. */ + git_hash_final_oid_fn fast_final_oid_fn; + /* The OID of the empty tree. */ const struct object_id *empty_tree; diff --git a/object-file.c b/object-file.c index c5994202ba0..9691292ef5a 100644 --- a/object-file.c +++ b/object-file.c @@ -115,6 +115,33 @@ static void git_hash_sha1_final_oid(struct object_id *oid, git_hash_ctx *ctx) oid->algo = GIT_HASH_SHA1; } +static void git_hash_sha1_init_fast(git_hash_ctx *ctx) +{ + git_SHA1_Init_fast(&ctx->sha1_fast); +} + +static void git_hash_sha1_clone_fast(git_hash_ctx *dst, const git_hash_ctx *src) +{ + git_SHA1_Clone_fast(&dst->sha1_fast, &src->sha1_fast); +} + +static void git_hash_sha1_update_fast(git_hash_ctx *ctx, const void *data, + size_t len) +{ + git_SHA1_Update_fast(&ctx->sha1_fast, data, len); +} + +static void git_hash_sha1_final_fast(unsigned char *hash, git_hash_ctx *ctx) +{ + git_SHA1_Final_fast(hash, &ctx->sha1_fast); +} + +static void git_hash_sha1_final_oid_fast(struct object_id *oid, git_hash_ctx *ctx) +{ + git_SHA1_Final_fast(oid->hash, &ctx->sha1_fast); + memset(oid->hash + GIT_SHA1_RAWSZ, 0, GIT_MAX_RAWSZ - GIT_SHA1_RAWSZ); + oid->algo = GIT_HASH_SHA1; +} static void git_hash_sha256_init(git_hash_ctx *ctx) { @@ -189,6 +216,11 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = { .update_fn = git_hash_unknown_update, .final_fn = git_hash_unknown_final, .final_oid_fn = git_hash_unknown_final_oid, + .fast_init_fn = git_hash_unknown_init, + .fast_clone_fn = git_hash_unknown_clone, + .fast_update_fn = git_hash_unknown_update, + .fast_final_fn = git_hash_unknown_final, + .fast_final_oid_fn = git_hash_unknown_final_oid, .empty_tree = NULL, .empty_blob = NULL, .null_oid = NULL, @@ -204,6 +236,11 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = { .update_fn = git_hash_sha1_update, .final_fn = git_hash_sha1_final, .final_oid_fn = git_hash_sha1_final_oid, + .fast_init_fn = git_hash_sha1_init_fast, + .fast_clone_fn = git_hash_sha1_clone_fast, + .fast_update_fn = git_hash_sha1_update_fast, + .fast_final_fn = git_hash_sha1_final_fast, + .fast_final_oid_fn = git_hash_sha1_final_oid_fast, .empty_tree = &empty_tree_oid, .empty_blob = &empty_blob_oid, .null_oid = &null_oid_sha1, @@ -219,6 +256,11 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = { .update_fn = git_hash_sha256_update, .final_fn = git_hash_sha256_final, .final_oid_fn = git_hash_sha256_final_oid, + .fast_init_fn = git_hash_sha256_init, + .fast_clone_fn = git_hash_sha256_clone, + .fast_update_fn = git_hash_sha256_update, + .fast_final_fn = git_hash_sha256_final, + .fast_final_oid_fn = git_hash_sha256_final_oid, .empty_tree = &empty_tree_oid_sha256, .empty_blob = &empty_blob_oid_sha256, .null_oid = &null_oid_sha256,