Port the CVE 2018-8897 mitigation to i386 ATF ptrace(2) tests
On i386 there is no need to switch execution mode. Use 0x23 SS selector for i386, amd64 used 0x4f. Based on pointers from <maxv>. Sponsored by <The NetBSD Foundation>
This commit is contained in:
kamil
parent
1a047feb17
commit
4ee7ae6051
@ -1,4 +1,4 @@
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/* $NetBSD: t_ptrace_amd64_wait.h,v 1.4 2018/05/14 12:42:34 kamil Exp $ */
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/* $NetBSD: t_ptrace_amd64_wait.h,v 1.5 2018/05/26 20:27:48 kamil Exp $ */
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/*-
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* Copyright (c) 2016 The NetBSD Foundation, Inc.
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@ -113,219 +113,9 @@ ATF_TC_BODY(x86_64_regs1, tc)
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/// ----------------------------------------------------------------------------
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ATF_TC(x86_64_cve_2018_8897);
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ATF_TC_HEAD(x86_64_cve_2018_8897, tc)
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{
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atf_tc_set_md_var(tc, "descr",
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"Verify mitigation for CVE-2018-8897 (POP SS debug exception)");
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}
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#define CVE_2018_8897_PAGE 0x5000 /* page addressable by 32-bit registers */
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static void
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trigger_cve_2018_8897(void)
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{
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/*
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* A function to trigger the POP SS (CVE-2018-8897) vulnerability
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*
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* We need to switch to 32-bit mode execution on 64-bit kernel.
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* This is achieved with far jump instruction and GDT descriptor
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* set to 32-bit CS selector. The 32-bit CS selector is kernel
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* specific, in the NetBSD case registered as GUCODE32_SEL
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* that is equal to (14 (decimal) << 3) with GDT and user
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* privilege level (this makes it 0x73).
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*
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* In UNIX as(1) assembly x86_64 far jump is coded as ljmp.
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* amd64 ljmp requires an indirect address with cs:RIP.
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*
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* When we are running in 32-bit mode, it's similar to the
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* mode as if the binary had been launched in netbsd32.
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*
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* There are two versions of this exploit, one with RIP
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* relative code and the other with static addresses.
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* The first one is PIE code aware, the other no-PIE one.
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*
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*
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* After switching to the 32-bit mode we can move on to the remaining
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* part of the exploit.
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*
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*
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* Set the stack pointer to the page we allocated earlier. Remember
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* that we put an SS selector exactly at this address, so we can pop.
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*
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* movl $0x5000,%esp
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*
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* Pop the SS selector off the stack. This reloads the SS selector,
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* which is fine. Remember that we set DR0 at address 0x5000, which
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* we are now reading. Therefore, on this instruction, the CPU will
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* raise a #DB exception.
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*
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* But the "pop %ss" instruction is special: it blocks exceptions
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* until the next instruction is executed. So the #DB that we just
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* raised is actually blocked.
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*
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* pop %ss
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*
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* We are still here, and didn't receive the #DB. After we execute
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* this instruction, the effect of "pop %ss" will disappear, and
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* we will receive the #DB for real.
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*
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* int $4
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*
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* Here the bug happens. We executed "int $4", so we entered the
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* kernel, with interrupts disabled. The #DB that was pending is
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* received. But, it is received immediately in kernel mode, and is
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* _NOT_ received when interrupts are enabled again.
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*
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* It means that, in the first instruction of the $4 handler, we
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* think we are safe with interrupts disabled. But we aren't, and
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* just got interrupted.
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*
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* The new interrupt handler doesn't handle this particular context:
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* we are entered in kernel mode, the previous context was kernel
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* mode too but it still had the user context loaded.
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*
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* We find ourselves not doing a 'swapgs'. At the end of the day, it
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* means that we call trap() with a curcpu() that is fully
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* controllable by userland. From then on, it is easy to escalate
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* privileges.
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*
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* With SVS it also means we don't switch CR3, so this results in a
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* triple fault, which this time cannot be turned to a privilege
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* escalation.
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*/
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#if __PIE__
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void *csRIP;
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csRIP = malloc(sizeof(int) + sizeof(short));
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FORKEE_ASSERT(csRIP != NULL);
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__asm__ __volatile__(
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" leal 24(%%eip), %%eax\n\t"
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" movq %0, %%rdx\n\t"
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" movl %%eax, (%%rdx)\n\t"
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" movw $0x73, 4(%%rdx)\n\t"
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" movq %1, %%rax\n\t"
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" ljmp *(%%rax)\n\t"
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" .code32\n\t"
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" movl $0x5000, %%esp\n\t"
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" pop %%ss\n\t"
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" int $4\n\t"
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" .code64\n\t"
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: "=m"(csRIP)
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: "m"(csRIP)
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: "%rax", "%rdx", "%rsp"
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);
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#else /* !__PIE__ */
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__asm__ __volatile__(
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" movq $farjmp32, %%rax\n\t"
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" ljmp *(%%rax)\n\t"
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"farjmp32:\n\t"
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" .long trigger32\n\t"
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" .word 0x73\n\t"
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" .code32\n\t"
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"trigger32:\n\t"
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" movl $0x5000, %%esp\n\t"
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" pop %%ss\n\t"
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" int $4\n\t"
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" .code64\n\t"
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:
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:
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: "%rax", "%rsp"
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);
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#endif
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}
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ATF_TC_BODY(x86_64_cve_2018_8897, tc)
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{
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const int sigval = SIGSTOP;
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pid_t child, wpid;
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#if defined(TWAIT_HAVE_STATUS)
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int status;
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#endif
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char *trap_page;
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struct dbreg db;
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if (!can_we_set_dbregs()) {
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atf_tc_skip("Either run this test as root or set sysctl(3) "
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"security.models.extensions.user_set_dbregs to 1");
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}
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DPRINTF("Before forking process PID=%d\n", getpid());
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SYSCALL_REQUIRE((child = fork()) != -1);
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if (child == 0) {
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DPRINTF("Before calling PT_TRACE_ME from child %d\n", getpid());
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FORKEE_ASSERT(ptrace(PT_TRACE_ME, 0, NULL, 0) != -1);
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trap_page = mmap((void *)CVE_2018_8897_PAGE,
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sysconf(_SC_PAGESIZE), PROT_READ|PROT_WRITE,
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MAP_FIXED|MAP_ANON|MAP_PRIVATE, -1, 0);
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/* trigger page fault */
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memset(trap_page, 0, sysconf(_SC_PAGESIZE));
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/* SS selector (descriptor 9 (0x4f >> 3)) */
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*trap_page = 0x4f;
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DPRINTF("Before raising %s from child\n", strsignal(sigval));
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FORKEE_ASSERT(raise(sigval) == 0);
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trigger_cve_2018_8897();
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/* NOTREACHED */
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FORKEE_ASSERTX(0 && "This shall not be reached");
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}
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DPRINTF("Parent process PID=%d, child's PID=%d\n", getpid(), child);
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DPRINTF("Before calling %s() for the child\n", TWAIT_FNAME);
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TWAIT_REQUIRE_SUCCESS(wpid = TWAIT_GENERIC(child, &status, 0), child);
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validate_status_stopped(status, sigval);
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DPRINTF("Call GETDBREGS for the child process\n");
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SYSCALL_REQUIRE(ptrace(PT_GETDBREGS, child, &db, 0) != -1);
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/*
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* Set up the dbregs. We put the 0x5000 address in DR0.
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* It means that, the first time we touch this, the CPU will trigger a
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* #DB exception.
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*/
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db.dr[0] = CVE_2018_8897_PAGE;
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db.dr[7] = 0x30003;
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DPRINTF("Call SETDBREGS for the child process\n");
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SYSCALL_REQUIRE(ptrace(PT_SETDBREGS, child, &db, 0) != -1);
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DPRINTF("Before resuming the child process where it left off and "
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"without signal to be sent\n");
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SYSCALL_REQUIRE(ptrace(PT_CONTINUE, child, (void *)1, 0) != -1);
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DPRINTF("Before calling %s() for the child\n", TWAIT_FNAME);
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TWAIT_REQUIRE_SUCCESS(wpid = TWAIT_GENERIC(child, &status, 0), child);
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// In this test we receive SIGFPE, is this appropriate?
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// validate_status_stopped(status, SIGFPE);
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DPRINTF("Kill the child process\n");
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SYSCALL_REQUIRE(ptrace(PT_KILL, child, NULL, 0) != -1);
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DPRINTF("Before calling %s() for the child\n", TWAIT_FNAME);
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TWAIT_REQUIRE_SUCCESS(wpid = TWAIT_GENERIC(child, &status, 0), child);
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validate_status_signaled(status, SIGKILL, 0);
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DPRINTF("Before calling %s() for the child\n", TWAIT_FNAME);
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TWAIT_REQUIRE_FAILURE(ECHILD, wpid = TWAIT_GENERIC(child, &status, 0));
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}
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#undef CVE_2018_8897_PAGE
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/// ----------------------------------------------------------------------------
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#define ATF_TP_ADD_TCS_PTRACE_WAIT_AMD64() \
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ATF_TP_ADD_TC_HAVE_GPREGS(tp, x86_64_regs1); \
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ATF_TP_ADD_TC_HAVE_GPREGS(tp, x86_64_cve_2018_8897);
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ATF_TP_ADD_TC_HAVE_GPREGS(tp, x86_64_regs1);
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#else
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#define ATF_TP_ADD_TCS_PTRACE_WAIT_AMD64()
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#endif
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@ -1,4 +1,4 @@
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/* $NetBSD: t_ptrace_x86_wait.h,v 1.6 2018/05/13 23:01:25 kamil Exp $ */
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/* $NetBSD: t_ptrace_x86_wait.h,v 1.7 2018/05/26 20:27:48 kamil Exp $ */
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/*-
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* Copyright (c) 2016 The NetBSD Foundation, Inc.
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@ -1956,6 +1956,238 @@ ATF_TC_BODY(dbregs_dr3_dont_inherit_execve, tc)
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{
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dbregs_dont_inherit_execve(3);
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}
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/// ----------------------------------------------------------------------------
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ATF_TC(x86_cve_2018_8897);
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ATF_TC_HEAD(x86_cve_2018_8897, tc)
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{
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atf_tc_set_md_var(tc, "descr",
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"Verify mitigation for CVE-2018-8897 (POP SS debug exception)");
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}
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#define X86_CVE_2018_8897_PAGE 0x5000 /* page addressable by 32-bit registers */
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static void
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x86_cve_2018_8897_trigger(void)
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{
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/*
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* A function to trigger the POP SS (CVE-2018-8897) vulnerability
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*
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* ifdef __x86_64__
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*
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* We need to switch to 32-bit mode execution on 64-bit kernel.
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* This is achieved with far jump instruction and GDT descriptor
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* set to 32-bit CS selector. The 32-bit CS selector is kernel
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* specific, in the NetBSD case registered as GUCODE32_SEL
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* that is equal to (14 (decimal) << 3) with GDT and user
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* privilege level (this makes it 0x73).
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*
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* In UNIX as(1) assembly x86_64 far jump is coded as ljmp.
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* amd64 ljmp requires an indirect address with cs:RIP.
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*
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* When we are running in 32-bit mode, it's similar to the
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* mode as if the binary had been launched in netbsd32.
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*
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* There are two versions of this exploit, one with RIP
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* relative code and the other with static addresses.
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* The first one is PIE code aware, the other no-PIE one.
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*
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*
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* After switching to the 32-bit mode we can move on to the remaining
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* part of the exploit.
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*
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* endif // __x86_64__
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*
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* Set the stack pointer to the page we allocated earlier. Remember
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* that we put an SS selector exactly at this address, so we can pop.
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*
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* movl $0x5000,%esp
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*
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* Pop the SS selector off the stack. This reloads the SS selector,
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* which is fine. Remember that we set DR0 at address 0x5000, which
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* we are now reading. Therefore, on this instruction, the CPU will
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* raise a #DB exception.
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*
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* But the "pop %ss" instruction is special: it blocks exceptions
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* until the next instruction is executed. So the #DB that we just
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* raised is actually blocked.
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*
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* pop %ss
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*
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* We are still here, and didn't receive the #DB. After we execute
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* this instruction, the effect of "pop %ss" will disappear, and
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* we will receive the #DB for real.
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*
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* int $4
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*
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* Here the bug happens. We executed "int $4", so we entered the
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* kernel, with interrupts disabled. The #DB that was pending is
|
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* received. But, it is received immediately in kernel mode, and is
|
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* _NOT_ received when interrupts are enabled again.
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*
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* It means that, in the first instruction of the $4 handler, we
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* think we are safe with interrupts disabled. But we aren't, and
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* just got interrupted.
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*
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* The new interrupt handler doesn't handle this particular context:
|
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* we are entered in kernel mode, the previous context was kernel
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* mode too but it still had the user context loaded.
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*
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* We find ourselves not doing a 'swapgs'. At the end of the day, it
|
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* means that we call trap() with a curcpu() that is fully
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* controllable by userland. From then on, it is easy to escalate
|
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* privileges.
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*
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* With SVS it also means we don't switch CR3, so this results in a
|
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* triple fault, which this time cannot be turned to a privilege
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* escalation.
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*/
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#if __x86_64__
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#if __PIE__
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void *csRIP;
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csRIP = malloc(sizeof(int) + sizeof(short));
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FORKEE_ASSERT(csRIP != NULL);
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__asm__ __volatile__(
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" leal 24(%%eip), %%eax\n\t"
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" movq %0, %%rdx\n\t"
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" movl %%eax, (%%rdx)\n\t"
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" movw $0x73, 4(%%rdx)\n\t"
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" movq %1, %%rax\n\t"
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" ljmp *(%%rax)\n\t"
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" .code32\n\t"
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" movl $0x5000, %%esp\n\t"
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" pop %%ss\n\t"
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" int $4\n\t"
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" .code64\n\t"
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: "=m"(csRIP)
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: "m"(csRIP)
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: "%rax", "%rdx", "%rsp"
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);
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#else /* !__PIE__ */
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__asm__ __volatile__(
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" movq $farjmp32, %%rax\n\t"
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" ljmp *(%%rax)\n\t"
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"farjmp32:\n\t"
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" .long trigger32\n\t"
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" .word 0x73\n\t"
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" .code32\n\t"
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"trigger32:\n\t"
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" movl $0x5000, %%esp\n\t"
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" pop %%ss\n\t"
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" int $4\n\t"
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" .code64\n\t"
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:
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:
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: "%rax", "%rsp"
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);
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#endif
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#elif __i386__
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__asm__ __volatile__(
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"movl $0x5000, %%esp\n\t"
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"pop %%ss\n\t"
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"int $4\n\t"
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:
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:
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: "%esp"
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);
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#endif
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}
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ATF_TC_BODY(x86_cve_2018_8897, tc)
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{
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const int sigval = SIGSTOP;
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pid_t child, wpid;
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#if defined(TWAIT_HAVE_STATUS)
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int status;
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#endif
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char *trap_page;
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struct dbreg db;
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if (!can_we_set_dbregs()) {
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atf_tc_skip("Either run this test as root or set sysctl(3) "
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"security.models.extensions.user_set_dbregs to 1");
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}
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DPRINTF("Before forking process PID=%d\n", getpid());
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SYSCALL_REQUIRE((child = fork()) != -1);
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if (child == 0) {
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DPRINTF("Before calling PT_TRACE_ME from child %d\n", getpid());
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FORKEE_ASSERT(ptrace(PT_TRACE_ME, 0, NULL, 0) != -1);
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trap_page = mmap((void *)X86_CVE_2018_8897_PAGE,
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sysconf(_SC_PAGESIZE), PROT_READ|PROT_WRITE,
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MAP_FIXED|MAP_ANON|MAP_PRIVATE, -1, 0);
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/* trigger page fault */
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memset(trap_page, 0, sysconf(_SC_PAGESIZE));
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// kernel GDT
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#if __x86_64__
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/* SS selector (descriptor 9 (0x4f >> 3)) */
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*trap_page = 0x4f;
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#elif __i386__
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/* SS selector (descriptor 4 (0x23 >> 3)) */
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*trap_page = 0x23;
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#endif
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DPRINTF("Before raising %s from child\n", strsignal(sigval));
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FORKEE_ASSERT(raise(sigval) == 0);
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x86_cve_2018_8897_trigger();
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/* NOTREACHED */
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FORKEE_ASSERTX(0 && "This shall not be reached");
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}
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DPRINTF("Parent process PID=%d, child's PID=%d\n", getpid(), child);
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DPRINTF("Before calling %s() for the child\n", TWAIT_FNAME);
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TWAIT_REQUIRE_SUCCESS(wpid = TWAIT_GENERIC(child, &status, 0), child);
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validate_status_stopped(status, sigval);
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DPRINTF("Call GETDBREGS for the child process\n");
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SYSCALL_REQUIRE(ptrace(PT_GETDBREGS, child, &db, 0) != -1);
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/*
|
||||
* Set up the dbregs. We put the 0x5000 address in DR0.
|
||||
* It means that, the first time we touch this, the CPU will trigger a
|
||||
* #DB exception.
|
||||
*/
|
||||
db.dr[0] = X86_CVE_2018_8897_PAGE;
|
||||
db.dr[7] = 0x30003;
|
||||
|
||||
DPRINTF("Call SETDBREGS for the child process\n");
|
||||
SYSCALL_REQUIRE(ptrace(PT_SETDBREGS, child, &db, 0) != -1);
|
||||
|
||||
DPRINTF("Before resuming the child process where it left off and "
|
||||
"without signal to be sent\n");
|
||||
SYSCALL_REQUIRE(ptrace(PT_CONTINUE, child, (void *)1, 0) != -1);
|
||||
|
||||
DPRINTF("Before calling %s() for the child\n", TWAIT_FNAME);
|
||||
TWAIT_REQUIRE_SUCCESS(wpid = TWAIT_GENERIC(child, &status, 0), child);
|
||||
|
||||
// In this test we receive SIGFPE, is this appropriate?
|
||||
// validate_status_stopped(status, SIGFPE);
|
||||
|
||||
DPRINTF("Kill the child process\n");
|
||||
SYSCALL_REQUIRE(ptrace(PT_KILL, child, NULL, 0) != -1);
|
||||
|
||||
DPRINTF("Before calling %s() for the child\n", TWAIT_FNAME);
|
||||
TWAIT_REQUIRE_SUCCESS(wpid = TWAIT_GENERIC(child, &status, 0), child);
|
||||
|
||||
validate_status_signaled(status, SIGKILL, 0);
|
||||
|
||||
DPRINTF("Before calling %s() for the child\n", TWAIT_FNAME);
|
||||
TWAIT_REQUIRE_FAILURE(ECHILD, wpid = TWAIT_GENERIC(child, &status, 0));
|
||||
}
|
||||
|
||||
/// ----------------------------------------------------------------------------
|
||||
|
||||
#define ATF_TP_ADD_TCS_PTRACE_WAIT_X86() \
|
||||
ATF_TP_ADD_TC_HAVE_DBREGS(tp, dbregs_print); \
|
||||
ATF_TP_ADD_TC_HAVE_DBREGS(tp, dbregs_preserve_dr0); \
|
||||
@ -2017,7 +2249,8 @@ ATF_TC_BODY(dbregs_dr3_dont_inherit_execve, tc)
|
||||
ATF_TP_ADD_TC_HAVE_DBREGS(tp, dbregs_dr0_dont_inherit_execve); \
|
||||
ATF_TP_ADD_TC_HAVE_DBREGS(tp, dbregs_dr1_dont_inherit_execve); \
|
||||
ATF_TP_ADD_TC_HAVE_DBREGS(tp, dbregs_dr2_dont_inherit_execve); \
|
||||
ATF_TP_ADD_TC_HAVE_DBREGS(tp, dbregs_dr3_dont_inherit_execve);
|
||||
ATF_TP_ADD_TC_HAVE_DBREGS(tp, dbregs_dr3_dont_inherit_execve); \
|
||||
ATF_TP_ADD_TC_HAVE_DBREGS(tp, x86_cve_2018_8897);
|
||||
#else
|
||||
#define ATF_TP_ADD_TCS_PTRACE_WAIT_X86()
|
||||
#endif
|
||||
|
||||
Loading…
Reference in New Issue
Block a user