kernel: add secalloc() and secfree() functions for secret memory allocation

The kernel needs to keep cryptographic keys and cipher states
confidential. secalloc() allocates memory from the secret pool
which is protected from debuggers reading the memory thru devproc.
secfree() releases the memory, overriding the data with garbage.

sys/src/9/port/alloc.c

@@ -53,8 +53,27 @@ static Pool pimagmem = {
 	.private=	&pimagpriv,
 };
 
+static Private psecrpriv;
+static Pool psecrmem = {
+	.name=	"Secrets",
+	.maxsize=	16*1024*1024,
+	.minarena=	64*1024,
+	.quantum=	32,
+	.alloc=	xalloc,
+	.merge=	xmerge,
+	.flags=	POOL_ANTAGONISM,
+
+	.lock=	plock,
+	.unlock=	punlock,
+	.print=	poolprint,
+	.panic=	ppanic,
+
+	.private=	&psecrpriv,
+};
+
 Pool*	mainmem = &pmainmem;
 Pool*	imagmem = &pimagmem;
+Pool*	secrmem = &psecrmem;
 
 /*
  * because we can't print while we're holding the locks, 
@@ -129,6 +148,7 @@ mallocsummary(void)
 {
 	poolsummary(mainmem);
 	poolsummary(imagmem);
+	poolsummary(secrmem);
 }
 
 /* everything from here down should be the same in libc, libdebugmalloc, and the kernel */
@@ -171,12 +191,9 @@ smalloc(ulong size)
 {
 	void *v;
 
-	for(;;) {
-		v = poolalloc(mainmem, size+Npadlong*sizeof(ulong));
-		if(v != nil)
-			break;
+	while((v = poolalloc(mainmem, size+Npadlong*sizeof(ulong))) == nil){
 		if(!waserror()){
-			resrcwait(0);
+			resrcwait(nil);
 			poperror();
 		}
 	}
@@ -278,6 +295,34 @@ calloc(ulong n, ulong szelem)
 	return v;
 }
 
+/* secret memory, used to back cryptographic keys and cipher states */
+void*
+secalloc(ulong size)
+{
+	void *v;
+
+	while((v = poolalloc(secrmem, size+Npadlong*sizeof(ulong))) == nil){
+		if(!waserror()){
+			resrcwait(nil);
+			poperror();
+		}
+	}
+	if(Npadlong){
+		v = (ulong*)v+Npadlong;
+		setmalloctag(v, getcallerpc(&size));
+		setrealloctag(v, 0);
+	}
+	memset(v, 0, size);
+	return v;
+}
+
+void
+secfree(void *v)
+{
+	if(v != nil)
+		poolfree(secrmem, (ulong*)v-Npadlong);
+}
+
 void
 setmalloctag(void *v, uintptr pc)
 {

sys/src/9/port/devproc.c

@@ -9,6 +9,8 @@
 #include	"ureg.h"
 #include	"edf.h"
 
+#include	<pool.h>
+
 enum
 {
 	Qdir,
@@ -789,7 +791,7 @@ procread(Chan *c, void *va, long n, vlong off)
 		if(addr < KZERO)
 			return procctlmemio(c, p, addr, va, n, 1);
 
-		if(!iseve())
+		if(!iseve() || poolisoverlap(secrmem, (uchar*)addr, n))
 			error(Eperm);
 
 		/* validate kernel addresses */

sys/src/9/port/portfns.h

@@ -308,6 +308,8 @@ void		sched(void);
 void		scheddump(void);
 void		schedinit(void);
 void		(*screenputs)(char*, int);
+void*		secalloc(ulong);
+void		secfree(void*);
 long		seconds(void);
 uintptr		segattach(int, char *, uintptr, uintptr);
 void		segclock(uintptr);