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Add ELF flag to disable ASLR stack gap.

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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
This commit is contained in:
Konstantin Belousov 2020-12-18 23:14:39 +00:00
parent c5354d593d
commit 673e2dd652
6 changed files with 16 additions and 6 deletions
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3
sys/compat/freebsd32/freebsd32_misc.c
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@ -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) {
/*

2
sys/kern/imgact_elf.c
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@ -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;

14
sys/kern/kern_exec.c
View File

@ -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) {
/*

1
sys/sys/elf_common.h
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@ -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. */

1
sys/sys/imgact.h
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@ -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

1
usr.bin/elfctl/elfctl.c
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@ -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[] = {