runtime/secret: implement new secret package

Implement secret.Do.

- When secret.Do returns:
  - Clear stack that is used by the argument function.
  - Clear all the registers that might contain secrets.
- On stack growth in secret mode, clear the old stack.
- When objects are allocated in secret mode, mark them and then zero
  the marked objects immediately when they are freed.
- If the argument function panics, raise that panic as if it originated
  from secret.Do. This removes anything about the secret function
  from tracebacks.

For now, this is only implemented on linux for arm64 and amd64.

This is a rebased version of Keith Randalls initial implementation at
CL 600635. I have added arm64 support, signal handling, preemption
handling and dealt with vDSOs spilling into system stacks.

Fixes #21865

Change-Id: I6fbd5a233beeaceb160785e0c0199a5c94d8e520
Co-authored-by: Keith Randall <khr@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/go/+/704615
Reviewed-by: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

1 files changed, 10 insertions, 8 deletions

diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 58eaf80237..cd75e2dd7c 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -549,6 +549,7 @@ type g struct {
 	syncSafePoint   bool // set if g is stopped at a synchronous safe point.
 	runningCleanups atomic.Bool
 	sig             uint32
+	secret          int32 // current nesting of runtime/secret.Do calls.
 	writebuf        []byte
 	sigcode0        uintptr
 	sigcode1        uintptr
@@ -620,14 +621,15 @@ type m struct {
 
 	// Fields whose offsets are not known to debuggers.
 
-	procid     uint64            // for debuggers, but offset not hard-coded
-	gsignal    *g                // signal-handling g
-	goSigStack gsignalStack      // Go-allocated signal handling stack
-	sigmask    sigset            // storage for saved signal mask
-	tls        [tlsSlots]uintptr // thread-local storage (for x86 extern register)
-	mstartfn   func()
-	curg       *g       // current running goroutine
-	caughtsig  guintptr // goroutine running during fatal signal
+	procid       uint64            // for debuggers, but offset not hard-coded
+	gsignal      *g                // signal-handling g
+	goSigStack   gsignalStack      // Go-allocated signal handling stack
+	sigmask      sigset            // storage for saved signal mask
+	tls          [tlsSlots]uintptr // thread-local storage (for x86 extern register)
+	mstartfn     func()
+	curg         *g       // current running goroutine
+	caughtsig    guintptr // goroutine running during fatal signal
+	signalSecret uint32   // whether we have secret information in our signal stack
 
 	// p is the currently attached P for executing Go code, nil if not executing user Go code.
 	//