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Apply mapping protections to preloaded kernel modules on amd64.

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With an upcoming change the amd64 kernel will map preloaded files RW
instead of RWX, so the kernel linker must adjust protections
appropriately using pmap_change_prot().

Reviewed by:	kib
MFC after:	1 month
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D21860
This commit is contained in:
Mark Johnston 2019-10-18 13:56:45 +00:00
parent 1d9eae9fb2
commit f822c9e287
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=353730
3 changed files with 72 additions and 4 deletions
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46
sys/kern/link_elf.c
View File

@ -736,9 +736,46 @@ parse_vnet(elf_file_t ef)
#endif
#undef LS_PADDING
/*
* Apply the specified protection to the loadable segments of a preloaded linker
* file.
*/
static int
link_elf_link_preload(linker_class_t cls,
const char* filename, linker_file_t *result)
preload_protect(elf_file_t ef, vm_prot_t prot)
{
#ifdef __amd64__
Elf_Ehdr *hdr;
Elf_Phdr *phdr, *phlimit;
vm_prot_t nprot;
int error;
error = 0;
hdr = (Elf_Ehdr *)ef->address;
phdr = (Elf_Phdr *)(ef->address + hdr->e_phoff);
phlimit = phdr + hdr->e_phnum;
for (; phdr < phlimit; phdr++) {
if (phdr->p_type != PT_LOAD)
continue;
nprot = prot | VM_PROT_READ;
if ((phdr->p_flags & PF_W) != 0)
nprot |= VM_PROT_WRITE;
if ((phdr->p_flags & PF_X) != 0)
nprot |= VM_PROT_EXECUTE;
error = pmap_change_prot((vm_offset_t)ef->address +
phdr->p_vaddr, round_page(phdr->p_memsz), nprot);
if (error != 0)
break;
}
return (error);
#else
return (0);
#endif
}
static int
link_elf_link_preload(linker_class_t cls, const char *filename,
linker_file_t *result)
{
Elf_Addr *ctors_addrp;
Elf_Size *ctors_sizep;
@ -798,6 +835,8 @@ link_elf_link_preload(linker_class_t cls,
if (error == 0)
error = parse_vnet(ef);
#endif
if (error == 0)
error = preload_protect(ef, VM_PROT_ALL);
if (error != 0) {
linker_file_unload(lf, LINKER_UNLOAD_FORCE);
return (error);
@ -815,6 +854,8 @@ link_elf_link_preload_finish(linker_file_t lf)
ef = (elf_file_t) lf;
error = relocate_file(ef);
if (error == 0)
error = preload_protect(ef, VM_PROT_NONE);
if (error != 0)
return (error);
(void)link_elf_preload_parse_symbols(ef);
@ -1274,6 +1315,7 @@ link_elf_unload_file(linker_file_t file)
static void
link_elf_unload_preload(linker_file_t file)
{
if (file->pathname != NULL)
preload_delete_name(file->pathname);
}

22
sys/kern/link_elf_obj.c
View File

@ -193,7 +193,6 @@ link_elf_init(void *arg)
linker_add_class(&link_elf_class);
}
SYSINIT(link_elf_obj, SI_SUB_KLD, SI_ORDER_SECOND, link_elf_init, NULL);
static void
@ -209,6 +208,15 @@ link_elf_protect_range(elf_file_t ef, vm_offset_t start, vm_offset_t end,
if (start == end)
return;
if (ef->preloaded) {
#ifdef __amd64__
error = pmap_change_prot(start, end - start, prot);
KASSERT(error == 0,
("link_elf_protect_range: pmap_change_prot() returned %d",
error));
#endif
return;
}
error = vm_map_protect(kernel_map, start, end, prot, FALSE);
KASSERT(error == KERN_SUCCESS,
("link_elf_protect_range: vm_map_protect() returned %d", error));
@ -564,6 +572,14 @@ link_elf_link_preload(linker_class_t cls, const char *filename,
goto out;
}
/*
* The file needs to be writeable and executable while applying
* relocations. Mapping protections are applied once relocation
* processing is complete.
*/
link_elf_protect_range(ef, (vm_offset_t)ef->address,
round_page((vm_offset_t)ef->address + ef->lf.size), VM_PROT_ALL);
/* Local intra-module relocations */
error = link_elf_reloc_local(lf, false);
if (error != 0)
@ -616,7 +632,9 @@ link_elf_link_preload_finish(linker_file_t lf)
return (error);
#endif
/* Invoke .ctors */
/* Apply protections now that relocation processing is complete. */
link_elf_protect(ef);
link_elf_invoke_ctors(lf->ctors_addr, lf->ctors_size);
return (0);
}

8
sys/vm/vm_kern.c
View File

@ -834,6 +834,14 @@ kmem_bootstrap_free(vm_offset_t start, vm_size_t size)
end = trunc_page(start + size);
start = round_page(start);
#ifdef __amd64__
/*
* Preloaded files do not have execute permissions by default on amd64.
* Restore the default permissions to ensure that the direct map alias
* is updated.
*/
pmap_change_prot(start, end - start, VM_PROT_RW);
#endif
for (va = start; va < end; va += PAGE_SIZE) {
pa = pmap_kextract(va);
m = PHYS_TO_VM_PAGE(pa);