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lkdtm: Add read/write after free tests for buddy memory

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The current tests for read/write after free work on slab
allocated memory. Memory straight from the buddy allocator
may behave slightly differently and have a different set
of parameters to test. Add tests for those cases as well.

On a basic x86 boot:

 # echo WRITE_BUDDY_AFTER_FREE > /sys/kernel/debug/provoke-crash/DIRECT
[   22.291950] lkdtm: Performing direct entry WRITE_BUDDY_AFTER_FREE
[   22.292983] lkdtm: Writing to the buddy page before free
[   22.293950] lkdtm: Attempting bad write to the buddy page after free

 # echo READ_BUDDY_AFTER_FREE > /sys/kernel/debug/provoke-crash/DIRECT
[   32.375601] lkdtm: Performing direct entry READ_BUDDY_AFTER_FREE
[   32.379896] lkdtm: Value in memory before free: 12345678
[   32.383854] lkdtm: Attempting to read from freed memory
[   32.389309] lkdtm: Buddy page was not poisoned

On x86 with CONFIG_DEBUG_PAGEALLOC and debug_pagealloc=on:

 # echo WRITE_BUDDY_AFTER_FREE > /sys/kernel/debug/provoke-crash/DIRECT
[   17.475533] lkdtm: Performing direct entry WRITE_BUDDY_AFTER_FREE
[   17.477360] lkdtm: Writing to the buddy page before free
[   17.479089] lkdtm: Attempting bad write to the buddy page after free
[   17.480904] BUG: unable to handle kernel paging request at
ffff88000ebd8000

 # echo READ_BUDDY_AFTER_FREE > /sys/kernel/debug/provoke-crash/DIRECT
[   14.606433] lkdtm: Performing direct entry READ_BUDDY_AFTER_FREE
[   14.607447] lkdtm: Value in memory before free: 12345678
[   14.608161] lkdtm: Attempting to read from freed memory
[   14.608860] BUG: unable to handle kernel paging request at
ffff88000eba3000

Note that arches without ARCH_SUPPORTS_DEBUG_PAGEALLOC may not
produce the same crash.

Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Laura Abbott 2016-02-25 16:36:44 -08:00 committed by Kees Cook
parent 250a8988ef
commit 920d451f9c
1 changed files with 45 additions and 0 deletions
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45
drivers/misc/lkdtm.c
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@ -93,6 +93,8 @@ enum ctype {
CT_OVERWRITE_ALLOCATION,
CT_WRITE_AFTER_FREE,
CT_READ_AFTER_FREE,
CT_WRITE_BUDDY_AFTER_FREE,
CT_READ_BUDDY_AFTER_FREE,
CT_SOFTLOCKUP,
CT_HARDLOCKUP,
CT_SPINLOCKUP,
@ -131,6 +133,8 @@ static char* cp_type[] = {
"OVERWRITE_ALLOCATION",
"WRITE_AFTER_FREE",
"READ_AFTER_FREE",
"WRITE_BUDDY_AFTER_FREE",
"READ_BUDDY_AFTER_FREE",
"SOFTLOCKUP",
"HARDLOCKUP",
"SPINLOCKUP",
@ -464,6 +468,47 @@ static void lkdtm_do_action(enum ctype which)
kfree(val);
break;
}
case CT_WRITE_BUDDY_AFTER_FREE: {
unsigned long p = __get_free_page(GFP_KERNEL);
if (!p)
break;
pr_info("Writing to the buddy page before free\n");
memset((void *)p, 0x3, PAGE_SIZE);
free_page(p);
schedule();
pr_info("Attempting bad write to the buddy page after free\n");
memset((void *)p, 0x78, PAGE_SIZE);
break;
}
case CT_READ_BUDDY_AFTER_FREE: {
unsigned long p = __get_free_page(GFP_KERNEL);
int saw, *val = kmalloc(1024, GFP_KERNEL);
int *base;
if (!p)
break;
if (!val)
break;
base = (int *)p;
*val = 0x12345678;
base[0] = *val;
pr_info("Value in memory before free: %x\n", base[0]);
free_page(p);
pr_info("Attempting to read from freed memory\n");
saw = base[0];
if (saw != *val) {
/* Good! Poisoning happened, so declare a win. */
pr_info("Buddy page correctly poisoned, calling BUG\n");
BUG();
}
pr_info("Buddy page was not poisoned\n");
kfree(val);
break;
}
case CT_SOFTLOCKUP:
preempt_disable();
for (;;)