From 758d98debec43ff83b8a1ed9a3d3a8441b83b3cc Mon Sep 17 00:00:00 2001 From: Mark Johnston Date: Mon, 17 Jan 2022 11:42:46 -0500 Subject: [PATCH] exec: Remove the stack gap implementation ASLR stack randomization will reappear in a forthcoming commit. Rather than inserting a random gap into the stack mapping, the entire stack mapping itself will be randomized in the same way that other mappings are when ASLR is enabled. No functional change intended, as the stack gap implementation is currently disabled by default. Reviewed by: kib MFC after: 2 weeks Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D33704 --- contrib/elftoolchain/readelf/readelf.c | 1 - sys/amd64/amd64/elf_machdep.c | 2 -- sys/arm64/arm64/elf_machdep.c | 1 - sys/compat/freebsd32/freebsd32_misc.c | 2 -- sys/compat/ia32/ia32_sysvec.c | 1 - sys/kern/imgact_elf.c | 19 ------------------- sys/kern/kern_exec.c | 20 -------------------- sys/sys/elf_common.h | 2 +- sys/sys/imgact.h | 2 -- sys/sys/imgact_elf.h | 1 - sys/sys/sysent.h | 1 - usr.bin/elfctl/elfctl.c | 2 -- 12 files changed, 1 insertion(+), 53 deletions(-) diff --git a/contrib/elftoolchain/readelf/readelf.c b/contrib/elftoolchain/readelf/readelf.c index 987a2ffb128..84855038d0e 100644 --- a/contrib/elftoolchain/readelf/readelf.c +++ b/contrib/elftoolchain/readelf/readelf.c @@ -3755,7 +3755,6 @@ static struct flag_desc note_feature_ctl_flags[] = { { NT_FREEBSD_FCTL_STKGAP_DISABLE, "STKGAP_DISABLE" }, { NT_FREEBSD_FCTL_WXNEEDED, "WXNEEDED" }, { NT_FREEBSD_FCTL_LA48, "LA48" }, - { NT_FREEBSD_FCTL_ASG_DISABLE, "ASG_DISABLE" }, { 0, NULL } }; diff --git a/sys/amd64/amd64/elf_machdep.c b/sys/amd64/amd64/elf_machdep.c index 645b9c08ea3..192a73e0a7d 100644 --- a/sys/amd64/amd64/elf_machdep.c +++ b/sys/amd64/amd64/elf_machdep.c @@ -92,7 +92,6 @@ struct sysentvec elf64_freebsd_sysvec_la48 = { .sv_schedtail = NULL, .sv_thread_detach = NULL, .sv_trap = NULL, - .sv_stackgap = elf64_stackgap, .sv_onexec_old = exec_onexec_old, .sv_onexit = exit_onexit, .sv_set_fork_retval = x86_set_fork_retval, @@ -135,7 +134,6 @@ struct sysentvec elf64_freebsd_sysvec_la57 = { .sv_schedtail = NULL, .sv_thread_detach = NULL, .sv_trap = NULL, - .sv_stackgap = elf64_stackgap, .sv_onexec_old = exec_onexec_old, .sv_onexit = exit_onexit, .sv_set_fork_retval= x86_set_fork_retval, diff --git a/sys/arm64/arm64/elf_machdep.c b/sys/arm64/arm64/elf_machdep.c index 09cd72b864c..3de0f82839e 100644 --- a/sys/arm64/arm64/elf_machdep.c +++ b/sys/arm64/arm64/elf_machdep.c @@ -94,7 +94,6 @@ static struct sysentvec elf64_freebsd_sysvec = { .sv_schedtail = NULL, .sv_thread_detach = NULL, .sv_trap = NULL, - .sv_stackgap = elf64_stackgap, .sv_hwcap = &elf_hwcap, .sv_hwcap2 = &elf_hwcap2, .sv_onexec_old = exec_onexec_old, diff --git a/sys/compat/freebsd32/freebsd32_misc.c b/sys/compat/freebsd32/freebsd32_misc.c index cc191d7ba75..60f46ad2cfb 100644 --- a/sys/compat/freebsd32/freebsd32_misc.c +++ b/sys/compat/freebsd32/freebsd32_misc.c @@ -3464,8 +3464,6 @@ freebsd32_copyout_strings(struct image_params *imgp, uintptr_t *stack_base) destp = rounddown2(destp, sizeof(uint32_t)); ustringp = destp; - exec_stackgap(imgp, &destp); - if (imgp->auxargs) { /* * Allocate room on the stack for the ELF auxargs diff --git a/sys/compat/ia32/ia32_sysvec.c b/sys/compat/ia32/ia32_sysvec.c index 7364a51a24a..540c2ef6fda 100644 --- a/sys/compat/ia32/ia32_sysvec.c +++ b/sys/compat/ia32/ia32_sysvec.c @@ -138,7 +138,6 @@ struct sysentvec ia32_freebsd_sysvec = { .sv_schedtail = NULL, .sv_thread_detach = NULL, .sv_trap = NULL, - .sv_stackgap = elf32_stackgap, .sv_onexec_old = exec_onexec_old, .sv_onexit = exit_onexit, .sv_set_fork_retval = x86_set_fork_retval, diff --git a/sys/kern/imgact_elf.c b/sys/kern/imgact_elf.c index 8852b47681f..c3d19064f6e 100644 --- a/sys/kern/imgact_elf.c +++ b/sys/kern/imgact_elf.c @@ -2757,22 +2757,3 @@ __elfN(untrans_prot)(vm_prot_t prot) flags |= PF_W; return (flags); } - -vm_size_t -__elfN(stackgap)(struct image_params *imgp, uintptr_t *stack_base) -{ - uintptr_t range, rbase, gap; - int pct; - - pct = __elfN(aslr_stack_gap); - if (pct == 0) - return (0); - if (pct > 50) - pct = 50; - range = imgp->eff_stack_sz * pct / 100; - arc4rand(&rbase, sizeof(rbase), 0); - gap = rbase % range; - gap &= ~(sizeof(u_long) - 1); - *stack_base -= gap; - return (gap); -} diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c index ee0209c6afa..09d2461e405 100644 --- a/sys/kern/kern_exec.c +++ b/sys/kern/kern_exec.c @@ -1200,9 +1200,6 @@ exec_new_vmspace(struct image_params *imgp, struct sysentvec *sv) } else { ssiz = maxssiz; } - imgp->eff_stack_sz = lim_cur(curthread, RLIMIT_STACK); - if (ssiz < imgp->eff_stack_sz) - imgp->eff_stack_sz = ssiz; stack_addr = sv->sv_usrstack - ssiz; stack_prot = obj != NULL && imgp->stack_prot != 0 ? imgp->stack_prot : sv->sv_stackprot; @@ -1557,21 +1554,6 @@ exec_args_get_begin_envv(struct image_args *args) return (args->endp); } -void -exec_stackgap(struct image_params *imgp, uintptr_t *dp) -{ - struct proc *p = imgp->proc; - - if (imgp->sysent->sv_stackgap == NULL || - (p->p_fctl0 & (NT_FREEBSD_FCTL_ASLR_DISABLE | - NT_FREEBSD_FCTL_ASG_DISABLE)) != 0 || - (imgp->map_flags & MAP_ASLR) == 0) { - p->p_vmspace->vm_stkgap = 0; - return; - } - p->p_vmspace->vm_stkgap = 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 @@ -1651,8 +1633,6 @@ exec_copyout_strings(struct image_params *imgp, uintptr_t *stack_base) destp = rounddown2(destp, sizeof(void *)); ustringp = destp; - exec_stackgap(imgp, &destp); - if (imgp->auxargs) { /* * Allocate room on the stack for the ELF auxargs diff --git a/sys/sys/elf_common.h b/sys/sys/elf_common.h index de09a2172f8..b8629fec8cb 100644 --- a/sys/sys/elf_common.h +++ b/sys/sys/elf_common.h @@ -804,7 +804,7 @@ 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 */ +/* was ASG_DISABLE, do not reuse 0x00000020 */ /* 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 0e99737a84a..70e5c2e8157 100644 --- a/sys/sys/imgact.h +++ b/sys/sys/imgact.h @@ -83,7 +83,6 @@ struct image_params { int pagesizeslen; vm_prot_t stack_prot; u_long stack_sz; - u_long eff_stack_sz; struct ucred *newcred; /* new credentials if changing */ #define IMGACT_SHELL 0x1 #define IMGACT_BINMISC 0x2 @@ -119,7 +118,6 @@ void exec_setregs(struct thread *, struct image_params *, uintptr_t); int exec_shell_imgact(struct image_params *); int exec_copyin_args(struct image_args *, const char *, enum uio_seg, char **, char **); -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/sys/sys/imgact_elf.h b/sys/sys/imgact_elf.h index 67b95207ec3..6890df5c150 100644 --- a/sys/sys/imgact_elf.h +++ b/sys/sys/imgact_elf.h @@ -118,7 +118,6 @@ int __elfN(remove_brand_entry)(Elf_Brandinfo *entry); int __elfN(freebsd_fixup)(uintptr_t *, struct image_params *); int __elfN(coredump)(struct thread *, struct vnode *, off_t, int); size_t __elfN(populate_note)(int, void *, void *, size_t, void **); -vm_size_t __elfN(stackgap)(struct image_params *, uintptr_t *); int __elfN(freebsd_copyout_auxargs)(struct image_params *, uintptr_t); void __elfN(puthdr)(struct thread *, void *, size_t, int, size_t, int); void __elfN(prepare_notes)(struct thread *, struct note_info_list *, diff --git a/sys/sys/sysent.h b/sys/sys/sysent.h index c401a0f5b3e..9883870891d 100644 --- a/sys/sys/sysent.h +++ b/sys/sys/sysent.h @@ -120,7 +120,6 @@ struct sysentvec { void (*sv_elf_core_prepare_notes)(struct thread *, struct note_info_list *, size_t *); int (*sv_imgact_try)(struct image_params *); - vm_size_t (*sv_stackgap)(struct image_params *, uintptr_t *); int (*sv_copyout_auxargs)(struct image_params *, uintptr_t); int sv_minsigstksz; /* minimum signal stack size */ diff --git a/usr.bin/elfctl/elfctl.c b/usr.bin/elfctl/elfctl.c index ef7f915ded3..de14551f76d 100644 --- a/usr.bin/elfctl/elfctl.c +++ b/usr.bin/elfctl/elfctl.c @@ -71,8 +71,6 @@ static struct ControlFeatures featurelist[] = { { "nostackgap", 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" }, - { "noaslrstkgap", NT_FREEBSD_FCTL_ASG_DISABLE, - "Disable ASLR stack gap" }, }; static struct option long_opts[] = {