lkdtm: Add read/write after free tests for buddy memory
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>
diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
index a00a2b1..8e00e2e 100644
--- a/drivers/misc/lkdtm.c
+++ b/drivers/misc/lkdtm.c
@@ -93,6 +93,8 @@
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 @@
"OVERWRITE_ALLOCATION",
"WRITE_AFTER_FREE",
"READ_AFTER_FREE",
+ "WRITE_BUDDY_AFTER_FREE",
+ "READ_BUDDY_AFTER_FREE",
"SOFTLOCKUP",
"HARDLOCKUP",
"SPINLOCKUP",
@@ -464,6 +468,47 @@
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 (;;)