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Code Issues Releases Activity

Implement enforcing write XOR execute mapping policy.

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It is checked in vm_map_insert() and vm_map_protect() that PROT_WRITE |
PROT_EXEC are never specified together, if vm_map has MAP_WX flag set.
FreeBSD control flag allows specific binary to request WX exempt, and
there are per ABI boolean sysctls kern.elf{32,64}.allow_wx to enable/
disable globally.

Reviewed by:	emaste, jhb
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D28050
This commit is contained in:
Konstantin Belousov 2021-01-09 00:40:04 +02:00
parent 2c52512caf
commit 2e1c94aa1f
4 changed files with 23 additions and 3 deletions
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8
sys/kern/imgact_elf.c
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@ -190,6 +190,11 @@ SYSCTL_INT(__CONCAT(_kern_elf, __ELF_WORD_SIZE), OID_AUTO, sigfastblock,
CTLFLAG_RWTUN, &__elfN(sigfastblock), 0,
"enable sigfastblock for new processes");
static bool __elfN(allow_wx) = true;
SYSCTL_BOOL(__CONCAT(_kern_elf, __ELF_WORD_SIZE), OID_AUTO, allow_wx,
CTLFLAG_RWTUN, &__elfN(allow_wx), 0,
"Allow pages to be mapped simultaneously writable and executable");
static Elf_Brandinfo *elf_brand_list[MAX_BRANDS];
#define aligned(a, t) (rounddown2((u_long)(a), sizeof(t)) == (u_long)(a))
@ -1237,6 +1242,9 @@ __CONCAT(exec_, __elfN(imgact))(struct image_params *imgp)
imgp->map_flags |= MAP_ASLR_IGNSTART;
}
if (!__elfN(allow_wx) && (fctl0 & NT_FREEBSD_FCTL_WXNEEDED) == 0)
imgp->map_flags |= MAP_WXORX;
error = exec_new_vmspace(imgp, sv);
vmspace = imgp->proc->p_vmspace;
map = &vmspace->vm_map;

6
sys/kern/kern_exec.c
View File

@ -1074,12 +1074,12 @@ exec_new_vmspace(struct image_params *imgp, struct sysentvec *sv)
pmap_remove_pages(vmspace_pmap(vmspace));
vm_map_remove(map, vm_map_min(map), vm_map_max(map));
/*
* An exec terminates mlockall(MCL_FUTURE), ASLR state
* must be re-evaluated.
* An exec terminates mlockall(MCL_FUTURE).
* ASLR and W^X states must be re-evaluated.
*/
vm_map_lock(map);
vm_map_modflags(map, 0, MAP_WIREFUTURE | MAP_ASLR |
MAP_ASLR_IGNSTART);
MAP_ASLR_IGNSTART | MAP_WXORX);
vm_map_unlock(map);
} else {
error = vmspace_exec(p, sv_minuser, sv->sv_maxuser);

11
sys/vm/vm_map.c
View File

@ -1671,6 +1671,10 @@ vm_map_insert(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
if (start == end || !vm_map_range_valid(map, start, end))
return (KERN_INVALID_ADDRESS);
if ((map->flags & MAP_WXORX) != 0 && (prot & (VM_PROT_WRITE |
VM_PROT_EXECUTE)) == (VM_PROT_WRITE | VM_PROT_EXECUTE))
return (KERN_PROTECTION_FAILURE);
/*
* Find the entry prior to the proposed starting address; if it's part
* of an existing entry, this range is bogus.
@ -2751,6 +2755,13 @@ vm_map_protect(vm_map_t map, vm_offset_t start, vm_offset_t end,
in_tran = NULL;
vm_map_lock(map);
if ((map->flags & MAP_WXORX) != 0 && (new_prot &
(VM_PROT_WRITE | VM_PROT_EXECUTE)) == (VM_PROT_WRITE |
VM_PROT_EXECUTE)) {
vm_map_unlock(map);
return (KERN_PROTECTION_FAILURE);
}
/*
* Ensure that we are not concurrently wiring pages. vm_map_wire() may
* need to fault pages into the map and will drop the map lock while

1
sys/vm/vm_map.h
View File

@ -228,6 +228,7 @@ struct vm_map {
#define MAP_ASLR 0x08 /* enabled ASLR */
#define MAP_ASLR_IGNSTART 0x10
#define MAP_REPLENISH 0x20
#define MAP_WXORX 0x40 /* enforce W^X */
#ifdef _KERNEL
#if defined(KLD_MODULE) && !defined(KLD_TIED)