git: ed52452d6e52 - MFC r368772: Add ELF flag to disable ASLR stack gap.

[Konstantin Belousov]

The branch stable/12 has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=ed52452d6e52a37409c15b13c0efca8d0b28c44e

commit ed52452d6e52a37409c15b13c0efca8d0b28c44e
Author:     Konstantin Belousov <kib at FreeBSD.org>
AuthorDate: 2020-12-18 23:14:39 +0000
Commit:     Konstantin Belousov <kib at FreeBSD.org>
CommitDate: 2020-12-25 13:44:33 +0000

    MFC r368772:
    Add ELF flag to disable ASLR stack gap.
    
    PR:     239873
    
    (cherry picked from commit 673e2dd652156342009930cf1f7d15623e4a543a)
---
 sys/compat/freebsd32/freebsd32_misc.c |  3 +--
 sys/kern/imgact_elf.c                 |  2 --
 sys/kern/kern_exec.c                  | 14 ++++++++++++--
 sys/sys/elf_common.h                  |  1 +
 sys/sys/imgact.h                      |  1 +
 usr.bin/elfctl/elfctl.c               |  1 +
 6 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/sys/compat/freebsd32/freebsd32_misc.c b/sys/compat/freebsd32/freebsd32_misc.c
index 76054c8046a0..6c9ede34c1dc 100644
--- a/sys/compat/freebsd32/freebsd32_misc.c
+++ b/sys/compat/freebsd32/freebsd32_misc.c
@@ -3224,9 +3224,8 @@ freebsd32_copyout_strings(struct image_params *imgp)
 	destp -= ARG_MAX - imgp->args->stringspace;
 	destp = rounddown2(destp, sizeof(uint32_t));
 
+	exec_stackgap(imgp, &destp);
 	vectp = (uint32_t *)destp;
-	if (imgp->sysent->sv_stackgap != NULL)
-		imgp->sysent->sv_stackgap(imgp, (u_long *)&vectp);
 
 	if (imgp->auxargs) {
 		/*
diff --git a/sys/kern/imgact_elf.c b/sys/kern/imgact_elf.c
index b1828591fc33..e436c34d1d1b 100644
--- a/sys/kern/imgact_elf.c
+++ b/sys/kern/imgact_elf.c
@@ -2757,8 +2757,6 @@ __elfN(stackgap)(struct image_params *imgp, u_long *stack_base)
 	u_long 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 cd6c231479bb..812d5e827093 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -1497,6 +1497,17 @@ exec_free_args(struct image_args *args)
 		fdescfree_remapped(args->fdp);
 }
 
+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
@@ -1574,9 +1585,8 @@ exec_copyout_strings(struct image_params *imgp)
 	destp -= ARG_MAX - imgp->args->stringspace;
 	destp = rounddown2(destp, sizeof(void *));
 
+	exec_stackgap(imgp, &destp);
 	vectp = (char **)destp;
-	if (imgp->sysent->sv_stackgap != NULL)
-		imgp->sysent->sv_stackgap(imgp, (u_long *)&vectp);
 
 	if (imgp->auxargs) {
 		/*
diff --git a/sys/sys/elf_common.h b/sys/sys/elf_common.h
index b31ee6db7179..c469557a96e1 100644
--- a/sys/sys/elf_common.h
+++ b/sys/sys/elf_common.h
@@ -791,6 +791,7 @@ 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 a89907e7b60d..44bf8a1359c9 100644
--- a/sys/sys/imgact.h
+++ b/sys/sys/imgact.h
@@ -110,6 +110,7 @@ int	exec_copyin_args(struct image_args *, 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 ccc1c85007ce..d18d828e151c 100644
--- a/usr.bin/elfctl/elfctl.c
+++ b/usr.bin/elfctl/elfctl.c
@@ -70,6 +70,7 @@ static struct ControlFeatures featurelist[] = {
 #ifdef NT_FREEBSD_FCTL_LA48
 	{ "la48",	NT_FREEBSD_FCTL_LA48, "amd64: Limit user VA to 48bit" },
 #endif
+	{ "aslrstkgap", NT_FREEBSD_FCTL_ASG_DISABLE, "Disable ASLR stack gap" },
 };
 
 static struct option long_opts[] = {