lkdtm: Check for SMEP clearing protections
This adds an x86-specific test for pinned cr4 bits. A successful test will validate pinning and check the ROP-style call-middle-of-function defense, if needed. For example, in the case of native_write_cr4() looking like this: ffffffff8171bce0 <native_write_cr4>: ffffffff8171bce0: 48 8b 35 79 46 f2 00 mov 0xf24679(%rip),%rsi ffffffff8171bce7: 48 09 f7 or %rsi,%rdi ffffffff8171bcea: 0f 22 e7 mov %rdi,%cr4 ... ffffffff8171bd5a: c3 retq The UNSET_SMEP test will jump to ffffffff8171bcea (the mov to cr4) instead of ffffffff8171bce0 (native_write_cr4() entry) to simulate a direct-call bypass attempt. Expected successful results: # echo UNSET_SMEP > /sys/kernel/debug/provoke-crash/DIRECT # dmesg [ 79.594433] lkdtm: Performing direct entry UNSET_SMEP [ 79.596459] lkdtm: trying to clear SMEP normally [ 79.598406] lkdtm: ok: SMEP did not get cleared [ 79.599981] lkdtm: trying to clear SMEP with call gadget [ 79.601810] ------------[ cut here ]------------ [ 79.603421] Attempt to unpin cr4 bits: 100000; bypass attack?! ... [ 79.650170] ---[ end trace 2452ca0f6126242e ]--- [ 79.650937] lkdtm: ok: SMEP removal was reverted Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
1909a671db
commit
06b32fdb03
|
@ -266,3 +266,69 @@ void lkdtm_STACK_GUARD_PAGE_TRAILING(void)
|
||||||
|
|
||||||
pr_err("FAIL: accessed page after stack!\n");
|
pr_err("FAIL: accessed page after stack!\n");
|
||||||
}
|
}
|
||||||
|
|
||||||
|
void lkdtm_UNSET_SMEP(void)
|
||||||
|
{
|
||||||
|
#ifdef CONFIG_X86_64
|
||||||
|
#define MOV_CR4_DEPTH 64
|
||||||
|
void (*direct_write_cr4)(unsigned long val);
|
||||||
|
unsigned char *insn;
|
||||||
|
unsigned long cr4;
|
||||||
|
int i;
|
||||||
|
|
||||||
|
cr4 = native_read_cr4();
|
||||||
|
|
||||||
|
if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) {
|
||||||
|
pr_err("FAIL: SMEP not in use\n");
|
||||||
|
return;
|
||||||
|
}
|
||||||
|
cr4 &= ~(X86_CR4_SMEP);
|
||||||
|
|
||||||
|
pr_info("trying to clear SMEP normally\n");
|
||||||
|
native_write_cr4(cr4);
|
||||||
|
if (cr4 == native_read_cr4()) {
|
||||||
|
pr_err("FAIL: pinning SMEP failed!\n");
|
||||||
|
cr4 |= X86_CR4_SMEP;
|
||||||
|
pr_info("restoring SMEP\n");
|
||||||
|
native_write_cr4(cr4);
|
||||||
|
return;
|
||||||
|
}
|
||||||
|
pr_info("ok: SMEP did not get cleared\n");
|
||||||
|
|
||||||
|
/*
|
||||||
|
* To test the post-write pinning verification we need to call
|
||||||
|
* directly into the middle of native_write_cr4() where the
|
||||||
|
* cr4 write happens, skipping any pinning. This searches for
|
||||||
|
* the cr4 writing instruction.
|
||||||
|
*/
|
||||||
|
insn = (unsigned char *)native_write_cr4;
|
||||||
|
for (i = 0; i < MOV_CR4_DEPTH; i++) {
|
||||||
|
/* mov %rdi, %cr4 */
|
||||||
|
if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7)
|
||||||
|
break;
|
||||||
|
/* mov %rdi,%rax; mov %rax, %cr4 */
|
||||||
|
if (insn[i] == 0x48 && insn[i+1] == 0x89 &&
|
||||||
|
insn[i+2] == 0xf8 && insn[i+3] == 0x0f &&
|
||||||
|
insn[i+4] == 0x22 && insn[i+5] == 0xe0)
|
||||||
|
break;
|
||||||
|
}
|
||||||
|
if (i >= MOV_CR4_DEPTH) {
|
||||||
|
pr_info("ok: cannot locate cr4 writing call gadget\n");
|
||||||
|
return;
|
||||||
|
}
|
||||||
|
direct_write_cr4 = (void *)(insn + i);
|
||||||
|
|
||||||
|
pr_info("trying to clear SMEP with call gadget\n");
|
||||||
|
direct_write_cr4(cr4);
|
||||||
|
if (native_read_cr4() & X86_CR4_SMEP) {
|
||||||
|
pr_info("ok: SMEP removal was reverted\n");
|
||||||
|
} else {
|
||||||
|
pr_err("FAIL: cleared SMEP not detected!\n");
|
||||||
|
cr4 |= X86_CR4_SMEP;
|
||||||
|
pr_info("restoring SMEP\n");
|
||||||
|
native_write_cr4(cr4);
|
||||||
|
}
|
||||||
|
#else
|
||||||
|
pr_err("FAIL: this test is x86_64-only\n");
|
||||||
|
#endif
|
||||||
|
}
|
||||||
|
|
|
@ -114,6 +114,7 @@ static const struct crashtype crashtypes[] = {
|
||||||
CRASHTYPE(CORRUPT_USER_DS),
|
CRASHTYPE(CORRUPT_USER_DS),
|
||||||
CRASHTYPE(STACK_GUARD_PAGE_LEADING),
|
CRASHTYPE(STACK_GUARD_PAGE_LEADING),
|
||||||
CRASHTYPE(STACK_GUARD_PAGE_TRAILING),
|
CRASHTYPE(STACK_GUARD_PAGE_TRAILING),
|
||||||
|
CRASHTYPE(UNSET_SMEP),
|
||||||
CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE),
|
CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE),
|
||||||
CRASHTYPE(OVERWRITE_ALLOCATION),
|
CRASHTYPE(OVERWRITE_ALLOCATION),
|
||||||
CRASHTYPE(WRITE_AFTER_FREE),
|
CRASHTYPE(WRITE_AFTER_FREE),
|
||||||
|
|
|
@ -26,6 +26,7 @@ void lkdtm_CORRUPT_LIST_DEL(void);
|
||||||
void lkdtm_CORRUPT_USER_DS(void);
|
void lkdtm_CORRUPT_USER_DS(void);
|
||||||
void lkdtm_STACK_GUARD_PAGE_LEADING(void);
|
void lkdtm_STACK_GUARD_PAGE_LEADING(void);
|
||||||
void lkdtm_STACK_GUARD_PAGE_TRAILING(void);
|
void lkdtm_STACK_GUARD_PAGE_TRAILING(void);
|
||||||
|
void lkdtm_UNSET_SMEP(void);
|
||||||
|
|
||||||
/* lkdtm_heap.c */
|
/* lkdtm_heap.c */
|
||||||
void lkdtm_OVERWRITE_ALLOCATION(void);
|
void lkdtm_OVERWRITE_ALLOCATION(void);
|
||||||
|
|
Loading…
Reference in a new issue