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

[Brandon Bergren]

Build broken on stable-12 i386 (detected by my local CI where I'm testing git CI):

17:26:24 --- kern_exec.o ---
17:26:24 /usr/src/sys/kern/kern_exec.c:1508:34: error: incompatible pointer types passing 'uintptr_t *' (aka 'unsigned int *') to parameter of type 'u_long *' (aka 'unsigned long *') [-Werror,-Wincompatible-pointer-types]
17:26:24         imgp->sysent->sv_stackgap(imgp, dp);
17:26:24                                         ^~


On Fri, Dec 25, 2020, at 7:47 AM, Konstantin Belousov wrote:
> 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[] = {
>

-- 
  Brandon Bergren
  bdragon at imap.cc