svn commit: r353730 - in head/sys: kern vm

[Mark Johnston]

Author: markj
Date: Fri Oct 18 13:56:45 2019
New Revision: 353730
URL: https://svnweb.freebsd.org/changeset/base/353730

Log:
  Apply mapping protections to preloaded kernel modules on amd64.
  
  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

Modified:
  head/sys/kern/link_elf.c
  head/sys/kern/link_elf_obj.c
  head/sys/vm/vm_kern.c

Modified: head/sys/kern/link_elf.c
==============================================================================
--- head/sys/kern/link_elf.c	Fri Oct 18 13:53:14 2019	(r353729)
+++ head/sys/kern/link_elf.c	Fri Oct 18 13:56:45 2019	(r353730)
@@ -736,10 +736,47 @@ 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;
 	caddr_t modptr, baseptr, sizeptr, dynptr;
@@ -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);
 }

Modified: head/sys/kern/link_elf_obj.c
==============================================================================
--- head/sys/kern/link_elf_obj.c	Fri Oct 18 13:53:14 2019	(r353729)
+++ head/sys/kern/link_elf_obj.c	Fri Oct 18 13:56:45 2019	(r353730)
@@ -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 star
 
 	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 *
 		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);
 }

Modified: head/sys/vm/vm_kern.c
==============================================================================
--- head/sys/vm/vm_kern.c	Fri Oct 18 13:53:14 2019	(r353729)
+++ head/sys/vm/vm_kern.c	Fri Oct 18 13:56:45 2019	(r353730)
@@ -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);