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Index: head/lib/libc/sys/procctl.2
===================================================================
--- head/lib/libc/sys/procctl.2
+++ head/lib/libc/sys/procctl.2
@@ -29,7 +29,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd April 9, 2019
+.Dd August 31, 2019
.Dt PROCCTL 2
.Os
.Sh NAME
@@ -503,6 +503,67 @@
.Vt int .
If signal delivery has not been requested, it will contain zero
on return.
+.It Dv PROC_STACKGAP_CTL
+Controls the stack gaps in the specified process.
+A stack gap is the part of the growth area for a
+.Dv MAP_STACK
+mapped region that is reserved and never filled by memory.
+Instead, the process is guaranteed to receive a
+.Dv SIGSEGV
+signal on accessing pages in the gap.
+Gaps protect against stack overflow corrupting memory adjacent
+to the stack.
+.Pp
+The
+.Fa data
+argument must point to an integer variable containing flags.
+The following flags are allowed:
+.Bl -tag -width PROC_STACKGAP_DISABLE_EXEC
+.It Dv PROC_STACKGAP_ENABLE
+This flag is only accepted for consistency with
+.Dv PROC_STACKGAP_STATUS .
+If stack gaps are enabled, the flag is ignored.
+If disabled, the flag causes an
+.Ev EINVAL
+error to be returned.
+After gaps are disabled in a process, they can only be re-enabled when an
+.Xr execve 2
+is performed.
+.It Dv PROC_STACKGAP_DISABLE
+Disable stack gaps for the process.
+For existing stacks, the gap is no longer a reserved part of the growth
+area and can be filled by memory on access.
+.It Dv PROC_STACKGAP_ENABLE_EXEC
+Enable stack gaps for programs started after an
+.Xr execve 2
+by the specified process.
+.It Dv PROC_STACKGAP_DISABLE_EXEC
+Inherit disabled stack gaps state after
+.Xr execve 2 .
+In other words, if the currently executing program has stack gaps disabled,
+they are kept disabled on exec.
+If gaps were enabled, they are kept enabled after exec.
+.El
+.Pp
+The stack gap state is inherited from the parent on
+.Xr fork 2 .
+.It Dv PROC_STACKGAP_STATUS
+Returns the current stack gap state for the specified process.
+.Fa data
+must point to an integer variable, which is used to return a bitmask
+consisting of the following flags:
+.Bl -tag -width PROC_STACKGAP_DISABLE_EXEC
+.It Dv PROC_STACKGAP_ENABLE
+Stack gaps are enabled.
+.It Dv PROC_STACKGAP_DISABLE
+Stack gaps are disabled.
+.It Dv PROC_STACKGAP_ENABLE_EXEC
+Stack gaps are enabled in the process after
+.Xr execve 2 .
+.It Dv PROC_STACKGAP_DISABLE_EXEC
+Stack gaps are disabled in the process after
+.Xr execve 2 .
+.El
.El
.Sh NOTES
Disabling tracing on a process should not be considered a security
Index: head/sys/compat/freebsd32/freebsd32_misc.c
===================================================================
--- head/sys/compat/freebsd32/freebsd32_misc.c
+++ head/sys/compat/freebsd32/freebsd32_misc.c
@@ -3364,6 +3364,7 @@
case PROC_ASLR_CTL:
case PROC_PROTMAX_CTL:
case PROC_SPROTECT:
+ case PROC_STACKGAP_CTL:
case PROC_TRACE_CTL:
case PROC_TRAPCAP_CTL:
error = copyin(PTRIN(uap->data), &flags, sizeof(flags));
@@ -3396,6 +3397,7 @@
break;
case PROC_ASLR_STATUS:
case PROC_PROTMAX_STATUS:
+ case PROC_STACKGAP_STATUS:
case PROC_TRACE_STATUS:
case PROC_TRAPCAP_STATUS:
data = &flags;
@@ -3426,6 +3428,7 @@
break;
case PROC_ASLR_STATUS:
case PROC_PROTMAX_STATUS:
+ case PROC_STACKGAP_STATUS:
case PROC_TRACE_STATUS:
case PROC_TRAPCAP_STATUS:
if (error == 0)
Index: head/sys/kern/kern_exec.c
===================================================================
--- head/sys/kern/kern_exec.c
+++ head/sys/kern/kern_exec.c
@@ -745,6 +745,8 @@
p->p_flag |= P_EXEC;
if ((p->p_flag2 & P2_NOTRACE_EXEC) == 0)
p->p_flag2 &= ~P2_NOTRACE;
+ if ((p->p_flag2 & P2_STKGAP_DISABLE_EXEC) == 0)
+ p->p_flag2 &= ~P2_STKGAP_DISABLE;
if (p->p_flag & P_PPWAIT) {
p->p_flag &= ~(P_PPWAIT | P_PPTRACE);
cv_broadcast(&p->p_pwait);
Index: head/sys/kern/kern_fork.c
===================================================================
--- head/sys/kern/kern_fork.c
+++ head/sys/kern/kern_fork.c
@@ -460,7 +460,8 @@
p2->p_flag = P_INMEM;
p2->p_flag2 = p1->p_flag2 & (P2_ASLR_DISABLE | P2_ASLR_ENABLE |
P2_ASLR_IGNSTART | P2_NOTRACE | P2_NOTRACE_EXEC |
- P2_PROTMAX_ENABLE | P2_PROTMAX_DISABLE | P2_TRAPCAP);
+ P2_PROTMAX_ENABLE | P2_PROTMAX_DISABLE | P2_TRAPCAP |
+ P2_STKGAP_DISABLE | P2_STKGAP_DISABLE_EXEC);
p2->p_swtick = ticks;
if (p1->p_flag & P_PROFIL)
startprofclock(p2);
Index: head/sys/kern/kern_procctl.c
===================================================================
--- head/sys/kern/kern_procctl.c
+++ head/sys/kern/kern_procctl.c
@@ -520,6 +520,55 @@
return (0);
}
+static int
+stackgap_ctl(struct thread *td, struct proc *p, int state)
+{
+ PROC_LOCK_ASSERT(p, MA_OWNED);
+
+ if ((state & ~(PROC_STACKGAP_ENABLE | PROC_STACKGAP_DISABLE |
+ PROC_STACKGAP_ENABLE_EXEC | PROC_STACKGAP_DISABLE_EXEC)) != 0)
+ return (EINVAL);
+ switch (state & (PROC_STACKGAP_ENABLE | PROC_STACKGAP_DISABLE)) {
+ case PROC_STACKGAP_ENABLE:
+ if ((p->p_flag2 & P2_STKGAP_DISABLE) != 0)
+ return (EINVAL);
+ break;
+ case PROC_STACKGAP_DISABLE:
+ p->p_flag2 |= P2_STKGAP_DISABLE;
+ break;
+ case 0:
+ break;
+ default:
+ return (EINVAL);
+ }
+ switch (state & (PROC_STACKGAP_ENABLE_EXEC |
+ PROC_STACKGAP_DISABLE_EXEC)) {
+ case PROC_STACKGAP_ENABLE_EXEC:
+ p->p_flag2 &= ~P2_STKGAP_DISABLE_EXEC;
+ break;
+ case PROC_STACKGAP_DISABLE_EXEC:
+ p->p_flag2 |= P2_STKGAP_DISABLE_EXEC;
+ break;
+ case 0:
+ break;
+ default:
+ return (EINVAL);
+ }
+ return (0);
+}
+
+static int
+stackgap_status(struct thread *td, struct proc *p, int *data)
+{
+ PROC_LOCK_ASSERT(p, MA_OWNED);
+
+ *data = (p->p_flag2 & P2_STKGAP_DISABLE) != 0 ? PROC_STACKGAP_DISABLE :
+ PROC_STACKGAP_ENABLE;
+ *data |= (p->p_flag2 & P2_STKGAP_DISABLE_EXEC) != 0 ?
+ PROC_STACKGAP_DISABLE_EXEC : PROC_STACKGAP_ENABLE_EXEC;
+ return (0);
+}
+
#ifndef _SYS_SYSPROTO_H_
struct procctl_args {
idtype_t idtype;
@@ -548,6 +597,7 @@
case PROC_ASLR_CTL:
case PROC_PROTMAX_CTL:
case PROC_SPROTECT:
+ case PROC_STACKGAP_CTL:
case PROC_TRACE_CTL:
case PROC_TRAPCAP_CTL:
error = copyin(uap->data, &flags, sizeof(flags));
@@ -578,6 +628,7 @@
break;
case PROC_ASLR_STATUS:
case PROC_PROTMAX_STATUS:
+ case PROC_STACKGAP_STATUS:
case PROC_TRACE_STATUS:
case PROC_TRAPCAP_STATUS:
data = &flags;
@@ -607,6 +658,7 @@
break;
case PROC_ASLR_STATUS:
case PROC_PROTMAX_STATUS:
+ case PROC_STACKGAP_STATUS:
case PROC_TRACE_STATUS:
case PROC_TRAPCAP_STATUS:
if (error == 0)
@@ -636,6 +688,10 @@
return (protmax_ctl(td, p, *(int *)data));
case PROC_PROTMAX_STATUS:
return (protmax_status(td, p, data));
+ case PROC_STACKGAP_CTL:
+ return (stackgap_ctl(td, p, *(int *)data));
+ case PROC_STACKGAP_STATUS:
+ return (stackgap_status(td, p, data));
case PROC_REAP_ACQUIRE:
return (reap_acquire(td, p));
case PROC_REAP_RELEASE:
@@ -678,6 +734,8 @@
case PROC_REAP_STATUS:
case PROC_REAP_GETPIDS:
case PROC_REAP_KILL:
+ case PROC_STACKGAP_CTL:
+ case PROC_STACKGAP_STATUS:
case PROC_TRACE_STATUS:
case PROC_TRAPCAP_STATUS:
case PROC_PDEATHSIG_CTL:
@@ -726,6 +784,8 @@
case PROC_ASLR_STATUS:
case PROC_PROTMAX_CTL:
case PROC_PROTMAX_STATUS:
+ case PROC_STACKGAP_CTL:
+ case PROC_STACKGAP_STATUS:
case PROC_TRACE_STATUS:
case PROC_TRAPCAP_STATUS:
tree_locked = false;
Index: head/sys/sys/proc.h
===================================================================
--- head/sys/sys/proc.h
+++ head/sys/sys/proc.h
@@ -762,6 +762,8 @@
#define P2_ASLR_IGNSTART 0x00000100 /* Enable ASLR to consume sbrk area. */
#define P2_PROTMAX_ENABLE 0x00000200 /* Force enable implied PROT_MAX. */
#define P2_PROTMAX_DISABLE 0x00000400 /* Force disable implied PROT_MAX. */
+#define P2_STKGAP_DISABLE 0x00000800 /* Disable stack gap for MAP_STACK */
+#define P2_STKGAP_DISABLE_EXEC 0x00001000 /* Stack gap disabled after exec */
/* Flags protected by proctree_lock, kept in p_treeflags. */
#define P_TREE_ORPHANED 0x00000001 /* Reparented, on orphan list */
Index: head/sys/sys/procctl.h
===================================================================
--- head/sys/sys/procctl.h
+++ head/sys/sys/procctl.h
@@ -61,6 +61,8 @@
#define PROC_ASLR_STATUS 14 /* query ASLR status */
#define PROC_PROTMAX_CTL 15 /* en/dis implicit PROT_MAX */
#define PROC_PROTMAX_STATUS 16 /* query implicit PROT_MAX status */
+#define PROC_STACKGAP_CTL 17 /* en/dis stack gap on MAP_STACK */
+#define PROC_STACKGAP_STATUS 18 /* query stack gap */
/* Operations for PROC_SPROTECT (passed in integer arg). */
#define PPROT_OP(x) ((x) & 0xf)
@@ -133,6 +135,11 @@
#define PROC_PROTMAX_FORCE_DISABLE 2
#define PROC_PROTMAX_NOFORCE 3
#define PROC_PROTMAX_ACTIVE 0x80000000
+
+#define PROC_STACKGAP_ENABLE 0x0001
+#define PROC_STACKGAP_DISABLE 0x0002
+#define PROC_STACKGAP_ENABLE_EXEC 0x0004
+#define PROC_STACKGAP_DISABLE_EXEC 0x0008
#ifndef _KERNEL
__BEGIN_DECLS
Index: head/sys/vm/vm_map.c
===================================================================
--- head/sys/vm/vm_map.c
+++ head/sys/vm/vm_map.c
@@ -4132,7 +4132,8 @@
addrbos + max_ssize > vm_map_max(map) ||
addrbos + max_ssize <= addrbos)
return (KERN_INVALID_ADDRESS);
- sgp = (vm_size_t)stack_guard_page * PAGE_SIZE;
+ sgp = (curproc->p_flag2 & P2_STKGAP_DISABLE) != 0 ? 0 :
+ (vm_size_t)stack_guard_page * PAGE_SIZE;
if (sgp >= max_ssize)
return (KERN_INVALID_ARGUMENT);
@@ -4183,6 +4184,8 @@
KASSERT((orient & MAP_STACK_GROWS_UP) == 0 ||
(new_entry->eflags & MAP_ENTRY_GROWS_UP) != 0,
("new entry lacks MAP_ENTRY_GROWS_UP"));
+ if (gap_bot == gap_top)
+ return (KERN_SUCCESS);
rv = vm_map_insert(map, NULL, 0, gap_bot, gap_top, VM_PROT_NONE,
VM_PROT_NONE, MAP_CREATE_GUARD | (orient == MAP_STACK_GROWS_DOWN ?
MAP_CREATE_STACK_GAP_DN : MAP_CREATE_STACK_GAP_UP));
@@ -4266,7 +4269,8 @@
} else {
return (KERN_FAILURE);
}
- guard = gap_entry->next_read;
+ guard = (curproc->p_flag2 & P2_STKGAP_DISABLE) != 0 ? 0 :
+ gap_entry->next_read;
max_grow = gap_entry->end - gap_entry->start;
if (guard > max_grow)
return (KERN_NO_SPACE);

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