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x86/mm: Remove CONFIG_DEBUG_NX_TEST

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CONFIG_DEBUG_NX_TEST has been broken since CONFIG_DEBUG_SET_MODULE_RONX=y
was added in v2.6.37 via:

  84e1c6bb38 ("x86: Add RO/NX protection for loadable kernel modules")

since the exception table was then made read-only.

Additionally, the manually constructed extables were never fixed when
relative extables were introduced in v3.5 via:

  706276543b ("x86, extable: Switch to relative exception table entries")

However, relative extables won't work for test_nx.c, since test instruction
memory areas may be more than INT_MAX away from an executable fixup
(e.g. stack and heap too far away from executable memory with the fixup).

Since clearly no one has been using this code for a while now, and similar
tests exist in LKDTM, this should just be removed entirely.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jinbum Park <jinb.park7@gmail.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170131003711.GA74048@beast
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Kees Cook 2017-01-30 16:37:11 -08:00 committed by Ingo Molnar
parent 459fbe0069
commit 3ad38ceb27
3 changed files with 0 additions and 182 deletions
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8
arch/x86/Kconfig.debug
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@ -120,14 +120,6 @@ config DEBUG_SET_MODULE_RONX
against certain classes of kernel exploits.
If in doubt, say "N".
config DEBUG_NX_TEST
tristate "Testcase for the NX non-executable stack feature"
depends on DEBUG_KERNEL && m
---help---
This option enables a testcase for the CPU NX capability
and the software setup of this feature.
If in doubt, say "N"
config DOUBLEFAULT
default y
bool "Enable doublefault exception handler" if EXPERT

1
arch/x86/kernel/Makefile
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@ -101,7 +101,6 @@ obj-$(CONFIG_APB_TIMER) += apb_timer.o
obj-$(CONFIG_AMD_NB) += amd_nb.o
obj-$(CONFIG_DEBUG_RODATA_TEST) += test_rodata.o
obj-$(CONFIG_DEBUG_NX_TEST) += test_nx.o
obj-$(CONFIG_DEBUG_NMI_SELFTEST) += nmi_selftest.o
obj-$(CONFIG_KVM_GUEST) += kvm.o kvmclock.o

173
arch/x86/kernel/test_nx.c
View File

@ -1,173 +0,0 @@
/*
* test_nx.c: functional test for NX functionality
*
* (C) Copyright 2008 Intel Corporation
* Author: Arjan van de Ven <arjan@linux.intel.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; version 2
* of the License.
*/
#include <linux/module.h>
#include <linux/sort.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <asm/asm.h>
extern int rodata_test_data;
/*
* This file checks 4 things:
* 1) Check if the stack is not executable
* 2) Check if kmalloc memory is not executable
* 3) Check if the .rodata section is not executable
* 4) Check if the .data section of a module is not executable
*
* To do this, the test code tries to execute memory in stack/kmalloc/etc,
* and then checks if the expected trap happens.
*
* Sadly, this implies having a dynamic exception handling table entry.
* ... which can be done (and will make Rusty cry)... but it can only
* be done in a stand-alone module with only 1 entry total.
* (otherwise we'd have to sort and that's just too messy)
*/
/*
* We want to set up an exception handling point on our stack,
* which means a variable value. This function is rather dirty
* and walks the exception table of the module, looking for a magic
* marker and replaces it with a specific function.
*/
static void fudze_exception_table(void *marker, void *new)
{
struct module *mod = THIS_MODULE;
struct exception_table_entry *extable;
/*
* Note: This module has only 1 exception table entry,
* so searching and sorting is not needed. If that changes,
* this would be the place to search and re-sort the exception
* table.
*/
if (mod->num_exentries > 1) {
printk(KERN_ERR "test_nx: too many exception table entries!\n");
printk(KERN_ERR "test_nx: test results are not reliable.\n");
return;
}
extable = (struct exception_table_entry *)mod->extable;
extable[0].insn = (unsigned long)new;
}
/*
* exception tables get their symbols translated so we need
* to use a fake function to put in there, which we can then
* replace at runtime.
*/
void foo_label(void);
/*
* returns 0 for not-executable, negative for executable
*
* Note: we cannot allow this function to be inlined, because
* that would give us more than 1 exception table entry.
* This in turn would break the assumptions above.
*/
static noinline int test_address(void *address)
{
unsigned long result;
/* Set up an exception table entry for our address */
fudze_exception_table(&foo_label, address);
result = 1;
asm volatile(
"foo_label:\n"
"0: call *%[fake_code]\n"
"1:\n"
".section .fixup,\"ax\"\n"
"2: mov %[zero], %[rslt]\n"
" ret\n"
".previous\n"
_ASM_EXTABLE(0b,2b)
: [rslt] "=r" (result)
: [fake_code] "r" (address), [zero] "r" (0UL), "0" (result)
);
/* change the exception table back for the next round */
fudze_exception_table(address, &foo_label);
if (result)
return -ENODEV;
return 0;
}
static unsigned char test_data = 0xC3; /* 0xC3 is the opcode for "ret" */
static int test_NX(void)
{
int ret = 0;
/* 0xC3 is the opcode for "ret" */
char stackcode[] = {0xC3, 0x90, 0 };
char *heap;
test_data = 0xC3;
printk(KERN_INFO "Testing NX protection\n");
/* Test 1: check if the stack is not executable */
if (test_address(&stackcode)) {
printk(KERN_ERR "test_nx: stack was executable\n");
ret = -ENODEV;
}
/* Test 2: Check if the heap is executable */
heap = kmalloc(64, GFP_KERNEL);
if (!heap)
return -ENOMEM;
heap[0] = 0xC3; /* opcode for "ret" */
if (test_address(heap)) {
printk(KERN_ERR "test_nx: heap was executable\n");
ret = -ENODEV;
}
kfree(heap);
/*
* The following 2 tests currently fail, this needs to get fixed
* Until then, don't run them to avoid too many people getting scared
* by the error message
*/
/* Test 3: Check if the .rodata section is executable */
if (rodata_test_data != 0xC3) {
printk(KERN_ERR "test_nx: .rodata marker has invalid value\n");
ret = -ENODEV;
} else if (test_address(&rodata_test_data)) {
printk(KERN_ERR "test_nx: .rodata section is executable\n");
ret = -ENODEV;
}
#if 0
/* Test 4: Check if the .data section of a module is executable */
if (test_address(&test_data)) {
printk(KERN_ERR "test_nx: .data section is executable\n");
ret = -ENODEV;
}
#endif
return ret;
}
static void test_exit(void)
{
}
module_init(test_NX);
module_exit(test_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Testcase for the NX infrastructure");
MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");