Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit f2c65fb3 authored by Nadav Amit's avatar Nadav Amit Committed by Ingo Molnar
Browse files

x86/modules: Avoid breaking W^X while loading modules 



When modules and BPF filters are loaded, there is a time window in
which some memory is both writable and executable. An attacker that has
already found another vulnerability (e.g., a dangling pointer) might be
able to exploit this behavior to overwrite kernel code. Prevent having
writable executable PTEs in this stage.

In addition, avoiding having W+X mappings can also slightly simplify the
patching of modules code on initialization (e.g., by alternatives and
static-key), as would be done in the next patch. This was actually the
main motivation for this patch.

To avoid having W+X mappings, set them initially as RW (NX) and after
they are set as RO set them as X as well. Setting them as executable is
done as a separate step to avoid one core in which the old PTE is cached
(hence writable), and another which sees the updated PTE (executable),
which would break the W^X protection.

Suggested-by: default avatarThomas Gleixner <tglx@linutronix.de>
Suggested-by: default avatarAndy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatarNadav Amit <namit@vmware.com>
Signed-off-by: default avatarRick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: <akpm@linux-foundation.org>
Cc: <ard.biesheuvel@linaro.org>
Cc: <deneen.t.dock@intel.com>
Cc: <kernel-hardening@lists.openwall.com>
Cc: <kristen@linux.intel.com>
Cc: <linux_dti@icloud.com>
Cc: <will.deacon@arm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Link: https://lkml.kernel.org/r/20190426001143.4983-12-namit@vmware.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 7298e24f

arch/x86/kernel/alternative.c

+21 −7
Original line number Diff line number Diff line
@@ -671,12 +671,26 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode, 
				       size_t len)

{

	unsigned long flags;



	if (boot_cpu_has(X86_FEATURE_NX) &&

	    is_module_text_address((unsigned long)addr)) {

		/*

		 * Modules text is marked initially as non-executable, so the

		 * code cannot be running and speculative code-fetches are

		 * prevented. Just change the code.

		 */

		memcpy(addr, opcode, len);

	} else {

		local_irq_save(flags);

		memcpy(addr, opcode, len);

		local_irq_restore(flags);

		sync_core();

	/* Could also do a CLFLUSH here to speed up CPU recovery; but

	   that causes hangs on some VIA CPUs. */



		/*

		 * Could also do a CLFLUSH here to speed up CPU recovery; but

		 * that causes hangs on some VIA CPUs.

		 */

	}

	return addr;

}

arch/x86/kernel/module.c

+1 −1
Original line number Diff line number Diff line
@@ -87,7 +87,7 @@ void *module_alloc(unsigned long size) 
	p = __vmalloc_node_range(size, MODULE_ALIGN,

				    MODULES_VADDR + get_module_load_offset(),

				    MODULES_END, GFP_KERNEL,

				    PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,

				    PAGE_KERNEL, 0, NUMA_NO_NODE,

				    __builtin_return_address(0));

	if (p && (kasan_module_alloc(p, size) < 0)) {

		vfree(p);

include/linux/filter.h

+1 −0
Original line number Diff line number Diff line
@@ -746,6 +746,7 @@ static inline void bpf_prog_unlock_ro(struct bpf_prog *fp) 
static inline void bpf_jit_binary_lock_ro(struct bpf_binary_header *hdr)

{

	set_memory_ro((unsigned long)hdr, hdr->pages);

	set_memory_x((unsigned long)hdr, hdr->pages);

}



static inline void bpf_jit_binary_unlock_ro(struct bpf_binary_header *hdr)

kernel/module.c

+5 −0
Original line number Diff line number Diff line
@@ -1950,8 +1950,13 @@ void module_enable_ro(const struct module *mod, bool after_init) 
		return;



	frob_text(&mod->core_layout, set_memory_ro);

	frob_text(&mod->core_layout, set_memory_x);



	frob_rodata(&mod->core_layout, set_memory_ro);



	frob_text(&mod->init_layout, set_memory_ro);

	frob_text(&mod->init_layout, set_memory_x);



	frob_rodata(&mod->init_layout, set_memory_ro);



	if (after_init)