Add ELF flag to disable ASLR stack gap.

Also centralize and unify checks to enable ASLR stack gap in a new
helper exec_stackgap().

PR:	239873
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

6 files changed, 16 insertions, 6 deletions

diff --git a/sys/compat/freebsd32/freebsd32_misc.c b/sys/compat/freebsd32/freebsd32_misc.c
index 6b7fd2deae35..62fab95c68d1 100644
--- a/sys/compat/freebsd32/freebsd32_misc.c
+++ b/sys/compat/freebsd32/freebsd32_misc.c
@@ -3424,8 +3424,7 @@ freebsd32_copyout_strings(struct image_params *imgp, uintptr_t *stack_base)
 	destp = rounddown2(destp, sizeof(uint32_t));
 	ustringp = destp;
 
-	if (imgp->sysent->sv_stackgap != NULL)
-		imgp->sysent->sv_stackgap(imgp, &destp);
+	exec_stackgap(imgp, &destp);
 
 	if (imgp->auxargs) {
 		/*
diff --git a/sys/kern/imgact_elf.c b/sys/kern/imgact_elf.c
index fc1b7bf1a53a..f6482bfcfb21 100644
--- a/sys/kern/imgact_elf.c
+++ b/sys/kern/imgact_elf.c
@@ -2818,8 +2818,6 @@ __elfN(stackgap)(struct image_params *imgp, uintptr_t *stack_base)
 	uintptr_t range, rbase, gap;
 	int pct;
 
-	if ((imgp->map_flags & MAP_ASLR) == 0)
-		return;
 	pct = __elfN(aslr_stack_gap);
 	if (pct == 0)
 		return;
diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index b3fcbef0289b..6f7c01470804 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -1534,6 +1534,17 @@ exec_args_get_begin_envv(struct image_args *args)
 	return (args->endp);
 }
 
+void
+exec_stackgap(struct image_params *imgp, uintptr_t *dp)
+{
+	if (imgp->sysent->sv_stackgap == NULL ||
+	    (imgp->proc->p_fctl0 & (NT_FREEBSD_FCTL_ASLR_DISABLE |
+	    NT_FREEBSD_FCTL_ASG_DISABLE)) != 0 ||
+	    (imgp->map_flags & MAP_ASLR) == 0)
+		return;
+	imgp->sysent->sv_stackgap(imgp, dp);
+}
+
 /*
  * Copy strings out to the new process address space, constructing new arg
  * and env vector tables. Return a pointer to the base so that it can be used
@@ -1624,8 +1635,7 @@ exec_copyout_strings(struct image_params *imgp, uintptr_t *stack_base)
 	destp = rounddown2(destp, sizeof(void *));
 	ustringp = destp;
 
-	if (imgp->sysent->sv_stackgap != NULL)
-		imgp->sysent->sv_stackgap(imgp, &destp);
+	exec_stackgap(imgp, &destp);
 
 	if (imgp->auxargs) {
 		/*
diff --git a/sys/sys/elf_common.h b/sys/sys/elf_common.h
index 8166d352955c..5724397754e7 100644
--- a/sys/sys/elf_common.h
+++ b/sys/sys/elf_common.h
@@ -797,6 +797,7 @@ typedef struct {
 #define	NT_FREEBSD_FCTL_STKGAP_DISABLE	0x00000004
 #define	NT_FREEBSD_FCTL_WXNEEDED	0x00000008
 #define	NT_FREEBSD_FCTL_LA48		0x00000010
+#define	NT_FREEBSD_FCTL_ASG_DISABLE	0x00000020 /* ASLR STACK GAP Disable */
 
 /* Values for n_type.  Used in core files. */
 #define	NT_PRSTATUS	1	/* Process status. */
diff --git a/sys/sys/imgact.h b/sys/sys/imgact.h
index 5463b6f80d1c..cd130551c050 100644
--- a/sys/sys/imgact.h
+++ b/sys/sys/imgact.h
@@ -122,6 +122,7 @@ int	exec_copyin_args(struct image_args *, const char *, enum uio_seg,
 	char **, char **);
 int	exec_copyin_data_fds(struct thread *, struct image_args *, const void *,
 	size_t, const int *, size_t);
+void	exec_stackgap(struct image_params *imgp, uintptr_t *dp);
 int	pre_execve(struct thread *td, struct vmspace **oldvmspace);
 void	post_execve(struct thread *td, int error, struct vmspace *oldvmspace);
 #endif
diff --git a/usr.bin/elfctl/elfctl.c b/usr.bin/elfctl/elfctl.c
index 591258fad729..e9b93e697ef7 100644
--- a/usr.bin/elfctl/elfctl.c
+++ b/usr.bin/elfctl/elfctl.c
@@ -68,6 +68,7 @@ static struct ControlFeatures featurelist[] = {
 	{ "stackgap",	NT_FREEBSD_FCTL_STKGAP_DISABLE, "Disable stack gap" },
 	{ "wxneeded",	NT_FREEBSD_FCTL_WXNEEDED, "Requires W+X mappings" },
 	{ "la48",	NT_FREEBSD_FCTL_LA48, "amd64: Limit user VA to 48bit" },
+	{ "aslrstkgap", NT_FREEBSD_FCTL_ASG_DISABLE, "Disable ASLR stack gap" },
 };
 
 static struct option long_opts[] = {