[dev.boringcrypto] crypto/ecdsa, crypto/rsa: use boring.Cache

In the original BoringCrypto port, ecdsa and rsa's public and private
keys added a 'boring unsafe.Pointer' field to cache the BoringCrypto
form of the key. This led to problems with code that “knew” the layout
of those structs and in particular that they had no unexported fields.

In response, as an awful kludge, I changed the compiler to pretend
that field did not exist when laying out reflect data. Because we want
to merge BoringCrypto in the main tree, we need a different solution.
Using boring.Cache is that solution.

For #51940.

Change-Id: Ideb2b40b599a1dc223082eda35a5ea9abcc01e30
Reviewed-on: https://go-review.googlesource.com/c/go/+/395883
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>

1 files changed, 9 insertions, 7 deletions

diff --git a/src/crypto/internal/boring/cache.go b/src/crypto/internal/boring/cache.go
index 4cf608368f..476e47706c 100644
--- a/src/crypto/internal/boring/cache.go
+++ b/src/crypto/internal/boring/cache.go
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build boringcrypto
-
 package boring
 
 import (
@@ -39,7 +37,7 @@ type cacheEntry struct {
 	next *cacheEntry    // immutable once linked into table
 }
 
-func registerCache(unsafe.Pointer)
+func registerCache(unsafe.Pointer) // provided by runtime
 
 // Register registers the cache with the runtime,
 // so that c.ptable can be cleared at the start of each GC.
@@ -106,7 +104,8 @@ func (c *Cache) Put(k, v unsafe.Pointer) {
 	//
 	//  1. We track in noK the start of the section of
 	//     the list that we've confirmed has no entry for k.
-	//     The next time down the list, we can stop at noK.
+	//     The next time down the list, we can stop at noK,
+	//     because new entries are inserted at the front of the list.
 	//     This guarantees we never traverse an entry
 	//     multiple times.
 	//
@@ -127,12 +126,15 @@ func (c *Cache) Put(k, v unsafe.Pointer) {
 		if add == nil {
 			add = &cacheEntry{k, v, nil}
 		}
-		if n < 1000 {
-			add.next = start
+		add.next = start
+		if n >= 1000 {
+			// If an individual list gets too long, which shouldn't happen,
+			// throw it away to avoid quadratic lookup behavior.
+			add.next = nil
 		}
 		if atomic.CompareAndSwapPointer(head, unsafe.Pointer(start), unsafe.Pointer(add)) {
 			return
 		}
-		noK = e
+		noK = start
 	}
 }