Create shared (readonly) page. Each ABI may specify the use of page by

setting SV_SHP flag and providing pointer to the vm object and mapping
address. Provide simple allocator to carve space in the page, tailored
to put the code with alignment restrictions.

Enable shared page use for amd64, both native and 32bit FreeBSD
binaries.  Page is private mapped at the top of the user address
space, moving a start of the stack one page down. Move signal
trampoline code from the top of the stack to the shared page.

Reviewed by:	 alc

1 files changed, 85 insertions, 4 deletions

diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index 1e4d690..6cf77f7 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -389,6 +389,7 @@ do_execve(td, args, mac_p)
 	imgp->canarylen = 0;
 	imgp->pagesizes = 0;
 	imgp->pagesizeslen = 0;
+	imgp->stack_prot = 0;
 
 #ifdef MAC
 	error = mac_execve_enter(imgp, mac_p);
@@ -996,6 +997,7 @@ exec_new_vmspace(imgp, sv)
 	int error;
 	struct proc *p = imgp->proc;
 	struct vmspace *vmspace = p->p_vmspace;
+	vm_object_t obj;
 	vm_offset_t sv_minuser, stack_addr;
 	vm_map_t map;
 	u_long ssiz;
@@ -1029,6 +1031,20 @@ exec_new_vmspace(imgp, sv)
 		map = &vmspace->vm_map;
 	}
 
+	/* Map a shared page */
+	obj = sv->sv_shared_page_obj;
+	if (obj != NULL) {
+		vm_object_reference(obj);
+		error = vm_map_fixed(map, obj, 0,
+		    sv->sv_shared_page_base, sv->sv_shared_page_len,
+		    VM_PROT_READ | VM_PROT_EXECUTE, VM_PROT_ALL,
+		    MAP_COPY_ON_WRITE | MAP_ACC_NO_CHARGE);
+		if (error) {
+			vm_object_deallocate(obj);
+			return (error);
+		}
+	}
+
 	/* Allocate a new stack */
 	if (sv->sv_maxssiz != NULL)
 		ssiz = *sv->sv_maxssiz;
@@ -1036,7 +1052,9 @@ exec_new_vmspace(imgp, sv)
 		ssiz = maxssiz;
 	stack_addr = sv->sv_usrstack - ssiz;
 	error = vm_map_stack(map, stack_addr, (vm_size_t)ssiz,
-	    sv->sv_stackprot, VM_PROT_ALL, MAP_STACK_GROWS_DOWN);
+	    obj != NULL && imgp->stack_prot != 0 ? imgp->stack_prot :
+		sv->sv_stackprot,
+	    VM_PROT_ALL, MAP_STACK_GROWS_DOWN);
 	if (error)
 		return (error);
 
@@ -1208,8 +1226,10 @@ exec_copyout_strings(imgp)
 	p = imgp->proc;
 	szsigcode = 0;
 	arginfo = (struct ps_strings *)p->p_sysent->sv_psstrings;
-	if (p->p_sysent->sv_szsigcode != NULL)
-		szsigcode = *(p->p_sysent->sv_szsigcode);
+	if (p->p_sysent->sv_sigcode_base == 0) {
+		if (p->p_sysent->sv_szsigcode != NULL)
+			szsigcode = *(p->p_sysent->sv_szsigcode);
+	}
 	destp =	(caddr_t)arginfo - szsigcode - SPARE_USRSPACE -
 	    roundup(execpath_len, sizeof(char *)) -
 	    roundup(sizeof(canary), sizeof(char *)) -
@@ -1219,7 +1239,7 @@ exec_copyout_strings(imgp)
 	/*
 	 * install sigcode
 	 */
-	if (szsigcode)
+	if (szsigcode != 0)
 		copyout(p->p_sysent->sv_sigcode, ((caddr_t)arginfo -
 		    szsigcode), szsigcode);
 
@@ -1459,3 +1479,64 @@ exec_unregister(execsw_arg)
 	execsw = newexecsw;
 	return (0);
 }
+
+static vm_object_t shared_page_obj;
+static int shared_page_free;
+
+int
+shared_page_fill(int size, int align, const char *data)
+{
+	vm_page_t m;
+	struct sf_buf *s;
+	vm_offset_t sk;
+	int res;
+
+	VM_OBJECT_LOCK(shared_page_obj);
+	m = vm_page_grab(shared_page_obj, 0, VM_ALLOC_RETRY);
+	res = roundup(shared_page_free, align);
+	if (res + size >= IDX_TO_OFF(shared_page_obj->size))
+		res = -1;
+	else {
+		VM_OBJECT_UNLOCK(shared_page_obj);
+		s = sf_buf_alloc(m, SFB_DEFAULT);
+		sk = sf_buf_kva(s);
+		bcopy(data, (void *)(sk + res), size);
+		shared_page_free = res + size;
+		sf_buf_free(s);
+		VM_OBJECT_LOCK(shared_page_obj);
+	}
+	vm_page_wakeup(m);
+	VM_OBJECT_UNLOCK(shared_page_obj);
+	return (res);
+}
+
+static void
+shared_page_init(void *dummy __unused)
+{
+	vm_page_t m;
+
+	shared_page_obj = vm_pager_allocate(OBJT_PHYS, 0, PAGE_SIZE,
+	    VM_PROT_DEFAULT, 0, NULL);
+	VM_OBJECT_LOCK(shared_page_obj);
+	m = vm_page_grab(shared_page_obj, 0, VM_ALLOC_RETRY | VM_ALLOC_NOBUSY |
+	    VM_ALLOC_ZERO);
+	m->valid = VM_PAGE_BITS_ALL;
+	VM_OBJECT_UNLOCK(shared_page_obj);
+}
+
+SYSINIT(shp, SI_SUB_EXEC, SI_ORDER_FIRST, (sysinit_cfunc_t)shared_page_init,
+    NULL);
+
+void
+exec_sysvec_init(void *param)
+{
+	struct sysentvec *sv;
+
+	sv = (struct sysentvec *)param;
+
+	if ((sv->sv_flags & SV_SHP) == 0)
+		return;
+	sv->sv_shared_page_obj = shared_page_obj;
+	sv->sv_sigcode_base = sv->sv_shared_page_base +
+	    shared_page_fill(*(sv->sv_szsigcode), 16, sv->sv_sigcode);
+}