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lkdtm: Verify that '__ro_after_init' works correctly 

The new __ro_after_init section should be writable before init, but
not after. Validate that it gets updated at init and can't be written
to afterwards.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Brown <david.brown@linaro.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Emese Revfy <re.emese@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathias Krause <minipli@googlemail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: PaX Team <pageexec@freemail.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-hardening@lists.openwall.com
Cc: linux-arch <linux-arch@vger.kernel.org>
Link: http://lkml.kernel.org/r/1455748879-21872-6-git-send-email-keescook@chromium.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Kees Cook 2016-02-17 14:41:16 -08:00 committed by Ingo Molnar
parent c74ba8b348
commit 7cca071ccb
1 changed files with 26 additions and 3 deletions
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29
drivers/misc/lkdtm.c
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@ -103,6 +103,7 @@ enum ctype {
CT_EXEC_USERSPACE,
CT_ACCESS_USERSPACE,
CT_WRITE_RO,
CT_WRITE_RO_AFTER_INIT,
CT_WRITE_KERN,
};
@ -140,6 +141,7 @@ static char* cp_type[] = {
"EXEC_USERSPACE",
"ACCESS_USERSPACE",
"WRITE_RO",
"WRITE_RO_AFTER_INIT",
"WRITE_KERN",
};
@ -162,6 +164,7 @@ static DEFINE_SPINLOCK(lock_me_up);
static u8 data_area[EXEC_SIZE];
static const unsigned long rodata = 0xAA55AA55;
static unsigned long ro_after_init __ro_after_init = 0x55AA5500;
module_param(recur_count, int, 0644);
MODULE_PARM_DESC(recur_count, " Recursion level for the stack overflow test");
@ -503,11 +506,28 @@ static void lkdtm_do_action(enum ctype which)
break;
}
case CT_WRITE_RO: {
unsigned long *ptr;
/* Explicitly cast away "const" for the test. */
unsigned long *ptr = (unsigned long *)&rodata;
ptr = (unsigned long *)&rodata;
pr_info("attempting bad rodata write at %p\n", ptr);
*ptr ^= 0xabcd1234;
pr_info("attempting bad write at %p\n", ptr);
break;
}
case CT_WRITE_RO_AFTER_INIT: {
unsigned long *ptr = &ro_after_init;
/*
* Verify we were written to during init. Since an Oops
* is considered a "success", a failure is to just skip the
* real test.
*/
if ((*ptr & 0xAA) != 0xAA) {
pr_info("%p was NOT written during init!?\n", ptr);
break;
}
pr_info("attempting bad ro_after_init write at %p\n", ptr);
*ptr ^= 0xabcd1234;
break;
@ -817,6 +837,9 @@ static int __init lkdtm_module_init(void)
int n_debugfs_entries = 1; /* Assume only the direct entry */
int i;
/* Make sure we can write to __ro_after_init values during __init */
ro_after_init |= 0xAA;
/* Register debugfs interface */
lkdtm_debugfs_root = debugfs_create_dir("provoke-crash", NULL);
if (!lkdtm_debugfs_root) {