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 <me@xxxxxxxxxxxx>
---
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 85f91516429..84dd7d0fab6 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,
--
2.46.0.430.gca674632b70
