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lkdtm: Avoid more compiler optimizations for bad writes

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It seems at least Clang is able to throw away writes it knows are
destined for read-only memory, which makes things like the WRITE_RO test
fail, as the write gets elided. Instead, force the variable to be
volatile, and make similar changes through-out other tests in an effort
to avoid needing to repeat fixing these kinds of problems. Also includes
pr_err() calls in failure paths so that kernel logs are more clear in
the failure case.

Reported-by: Prasad Sodagudi <psodagud@codeaurora.org>
Suggested-by: Sami Tolvanen <samitolvanen@google.com>
Fixes: 9ae113ce5f ("lkdtm: add tests for additional page permissions")
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200625203704.317097-2-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Kees Cook 2020-06-25 13:37:01 -07:00 committed by Greg Kroah-Hartman
parent 4afc339ef0
commit 464e86b4ab
3 changed files with 25 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
drivers/misc/lkdtm/bugs.c
View File

@ -118,9 +118,8 @@ noinline void lkdtm_CORRUPT_STACK(void)
/* Use default char array length that triggers stack protection. */
char data[8] __aligned(sizeof(void *));
__lkdtm_CORRUPT_STACK(&data);
pr_info("Corrupted stack containing char array ...\n");
pr_info("Corrupting stack containing char array ...\n");
__lkdtm_CORRUPT_STACK((void *)&data);
}
/* Same as above but will only get a canary with -fstack-protector-strong */
@ -131,9 +130,8 @@ noinline void lkdtm_CORRUPT_STACK_STRONG(void)
unsigned long *ptr;
} data __aligned(sizeof(void *));
__lkdtm_CORRUPT_STACK(&data);
pr_info("Corrupted stack containing union ...\n");
pr_info("Corrupting stack containing union ...\n");
__lkdtm_CORRUPT_STACK((void *)&data);
}
void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
@ -248,6 +246,7 @@ void lkdtm_ARRAY_BOUNDS(void)
kfree(not_checked);
kfree(checked);
pr_err("FAIL: survived array bounds overflow!\n");
}
void lkdtm_CORRUPT_LIST_ADD(void)

22
drivers/misc/lkdtm/perms.c
View File

@ -57,6 +57,7 @@ static noinline void execute_location(void *dst, bool write)
}
pr_info("attempting bad execution at %px\n", func);
func();
pr_err("FAIL: func returned\n");
}
static void execute_user_location(void *dst)
@ -75,20 +76,22 @@ static void execute_user_location(void *dst)
return;
pr_info("attempting bad execution at %px\n", func);
func();
pr_err("FAIL: func returned\n");
}
void lkdtm_WRITE_RO(void)
{
/* Explicitly cast away "const" for the test. */
unsigned long *ptr = (unsigned long *)&rodata;
/* Explicitly cast away "const" for the test and make volatile. */
volatile unsigned long *ptr = (unsigned long *)&rodata;
pr_info("attempting bad rodata write at %px\n", ptr);
*ptr ^= 0xabcd1234;
pr_err("FAIL: survived bad write\n");
}
void lkdtm_WRITE_RO_AFTER_INIT(void)
{
unsigned long *ptr = &ro_after_init;
volatile unsigned long *ptr = &ro_after_init;
/*
* Verify we were written to during init. Since an Oops
@ -102,19 +105,21 @@ void lkdtm_WRITE_RO_AFTER_INIT(void)
pr_info("attempting bad ro_after_init write at %px\n", ptr);
*ptr ^= 0xabcd1234;
pr_err("FAIL: survived bad write\n");
}
void lkdtm_WRITE_KERN(void)
{
size_t size;
unsigned char *ptr;
volatile unsigned char *ptr;
size = (unsigned long)do_overwritten - (unsigned long)do_nothing;
ptr = (unsigned char *)do_overwritten;
pr_info("attempting bad %zu byte write at %px\n", size, ptr);
memcpy(ptr, (unsigned char *)do_nothing, size);
memcpy((void *)ptr, (unsigned char *)do_nothing, size);
flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size));
pr_err("FAIL: survived bad write\n");
do_overwritten();
}
@ -193,9 +198,11 @@ void lkdtm_ACCESS_USERSPACE(void)
pr_info("attempting bad read at %px\n", ptr);
tmp = *ptr;
tmp += 0xc0dec0de;
pr_err("FAIL: survived bad read\n");
pr_info("attempting bad write at %px\n", ptr);
*ptr = tmp;
pr_err("FAIL: survived bad write\n");
vm_munmap(user_addr, PAGE_SIZE);
}
@ -203,19 +210,20 @@ void lkdtm_ACCESS_USERSPACE(void)
void lkdtm_ACCESS_NULL(void)
{
unsigned long tmp;
unsigned long *ptr = (unsigned long *)NULL;
volatile unsigned long *ptr = (unsigned long *)NULL;
pr_info("attempting bad read at %px\n", ptr);
tmp = *ptr;
tmp += 0xc0dec0de;
pr_err("FAIL: survived bad read\n");
pr_info("attempting bad write at %px\n", ptr);
*ptr = tmp;
pr_err("FAIL: survived bad write\n");
}
void __init lkdtm_perms_init(void)
{
/* Make sure we can write to __ro_after_init values during __init */
ro_after_init |= 0xAA;
}

7
drivers/misc/lkdtm/usercopy.c
View File

@ -304,19 +304,22 @@ void lkdtm_USERCOPY_KERNEL(void)
return;
}
pr_info("attempting good copy_to_user from kernel rodata\n");
pr_info("attempting good copy_to_user from kernel rodata: %px\n",
test_text);
if (copy_to_user((void __user *)user_addr, test_text,
unconst + sizeof(test_text))) {
pr_warn("copy_to_user failed unexpectedly?!\n");
goto free_user;
}
pr_info("attempting bad copy_to_user from kernel text\n");
pr_info("attempting bad copy_to_user from kernel text: %px\n",
vm_mmap);
if (copy_to_user((void __user *)user_addr, vm_mmap,
unconst + PAGE_SIZE)) {
pr_warn("copy_to_user failed, but lacked Oops\n");
goto free_user;
}
pr_err("FAIL: survived bad copy_to_user()\n");
free_user:
vm_munmap(user_addr, PAGE_SIZE);