287 lines
7.7 KiB
C
287 lines
7.7 KiB
C
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/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* mov_ss_trap.c: Exercise the bizarre side effects of a watchpoint on MOV SS
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*
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* This does MOV SS from a watchpointed address followed by various
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* types of kernel entries. A MOV SS that hits a watchpoint will queue
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* up a #DB trap but will not actually deliver that trap. The trap
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* will be delivered after the next instruction instead. The CPU's logic
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* seems to be:
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*
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* - Any fault: drop the pending #DB trap.
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* - INT $N, INT3, INTO, SYSCALL, SYSENTER: enter the kernel and then
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* deliver #DB.
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* - ICEBP: enter the kernel but do not deliver the watchpoint trap
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* - breakpoint: only one #DB is delivered (phew!)
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*
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* There are plenty of ways for a kernel to handle this incorrectly. This
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* test tries to exercise all the cases.
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*
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* This should mostly cover CVE-2018-1087 and CVE-2018-8897.
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*/
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#define _GNU_SOURCE
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#include <stdlib.h>
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#include <sys/ptrace.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <sys/user.h>
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#include <sys/syscall.h>
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#include <unistd.h>
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#include <errno.h>
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#include <stddef.h>
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#include <stdio.h>
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#include <err.h>
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#include <string.h>
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#include <setjmp.h>
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#include <sys/prctl.h>
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#define X86_EFLAGS_RF (1UL << 16)
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#if __x86_64__
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# define REG_IP REG_RIP
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#else
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# define REG_IP REG_EIP
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#endif
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unsigned short ss;
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extern unsigned char breakpoint_insn[];
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sigjmp_buf jmpbuf;
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static void enable_watchpoint(void)
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{
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pid_t parent = getpid();
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int status;
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pid_t child = fork();
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if (child < 0)
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err(1, "fork");
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if (child) {
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if (waitpid(child, &status, 0) != child)
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err(1, "waitpid for child");
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} else {
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unsigned long dr0, dr1, dr7;
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dr0 = (unsigned long)&ss;
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dr1 = (unsigned long)breakpoint_insn;
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dr7 = ((1UL << 1) | /* G0 */
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(3UL << 16) | /* RW0 = read or write */
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(1UL << 18) | /* LEN0 = 2 bytes */
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(1UL << 3)); /* G1, RW1 = insn */
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if (ptrace(PTRACE_ATTACH, parent, NULL, NULL) != 0)
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err(1, "PTRACE_ATTACH");
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if (waitpid(parent, &status, 0) != parent)
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err(1, "waitpid for child");
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if (ptrace(PTRACE_POKEUSER, parent, (void *)offsetof(struct user, u_debugreg[0]), dr0) != 0)
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err(1, "PTRACE_POKEUSER DR0");
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if (ptrace(PTRACE_POKEUSER, parent, (void *)offsetof(struct user, u_debugreg[1]), dr1) != 0)
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err(1, "PTRACE_POKEUSER DR1");
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if (ptrace(PTRACE_POKEUSER, parent, (void *)offsetof(struct user, u_debugreg[7]), dr7) != 0)
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err(1, "PTRACE_POKEUSER DR7");
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printf("\tDR0 = %lx, DR1 = %lx, DR7 = %lx\n", dr0, dr1, dr7);
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if (ptrace(PTRACE_DETACH, parent, NULL, NULL) != 0)
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err(1, "PTRACE_DETACH");
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exit(0);
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}
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}
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static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
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int flags)
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{
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struct sigaction sa;
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memset(&sa, 0, sizeof(sa));
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sa.sa_sigaction = handler;
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sa.sa_flags = SA_SIGINFO | flags;
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sigemptyset(&sa.sa_mask);
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if (sigaction(sig, &sa, 0))
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err(1, "sigaction");
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}
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static char const * const signames[] = {
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[SIGSEGV] = "SIGSEGV",
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[SIGBUS] = "SIBGUS",
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[SIGTRAP] = "SIGTRAP",
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[SIGILL] = "SIGILL",
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};
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static void sigtrap(int sig, siginfo_t *si, void *ctx_void)
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{
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ucontext_t *ctx = ctx_void;
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printf("\tGot SIGTRAP with RIP=%lx, EFLAGS.RF=%d\n",
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(unsigned long)ctx->uc_mcontext.gregs[REG_IP],
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!!(ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_RF));
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}
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static void handle_and_return(int sig, siginfo_t *si, void *ctx_void)
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{
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ucontext_t *ctx = ctx_void;
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printf("\tGot %s with RIP=%lx\n", signames[sig],
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(unsigned long)ctx->uc_mcontext.gregs[REG_IP]);
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}
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static void handle_and_longjmp(int sig, siginfo_t *si, void *ctx_void)
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{
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ucontext_t *ctx = ctx_void;
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printf("\tGot %s with RIP=%lx\n", signames[sig],
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(unsigned long)ctx->uc_mcontext.gregs[REG_IP]);
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siglongjmp(jmpbuf, 1);
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}
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int main()
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{
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unsigned long nr;
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asm volatile ("mov %%ss, %[ss]" : [ss] "=m" (ss));
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printf("\tSS = 0x%hx, &SS = 0x%p\n", ss, &ss);
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if (prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0) == 0)
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printf("\tPR_SET_PTRACER_ANY succeeded\n");
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printf("\tSet up a watchpoint\n");
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sethandler(SIGTRAP, sigtrap, 0);
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enable_watchpoint();
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printf("[RUN]\tRead from watched memory (should get SIGTRAP)\n");
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asm volatile ("mov %[ss], %[tmp]" : [tmp] "=r" (nr) : [ss] "m" (ss));
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printf("[RUN]\tMOV SS; INT3\n");
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asm volatile ("mov %[ss], %%ss; int3" :: [ss] "m" (ss));
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printf("[RUN]\tMOV SS; INT 3\n");
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asm volatile ("mov %[ss], %%ss; .byte 0xcd, 0x3" :: [ss] "m" (ss));
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printf("[RUN]\tMOV SS; CS CS INT3\n");
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asm volatile ("mov %[ss], %%ss; .byte 0x2e, 0x2e; int3" :: [ss] "m" (ss));
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printf("[RUN]\tMOV SS; CSx14 INT3\n");
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asm volatile ("mov %[ss], %%ss; .fill 14,1,0x2e; int3" :: [ss] "m" (ss));
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printf("[RUN]\tMOV SS; INT 4\n");
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sethandler(SIGSEGV, handle_and_return, SA_RESETHAND);
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asm volatile ("mov %[ss], %%ss; int $4" :: [ss] "m" (ss));
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#ifdef __i386__
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printf("[RUN]\tMOV SS; INTO\n");
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sethandler(SIGSEGV, handle_and_return, SA_RESETHAND);
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nr = -1;
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asm volatile ("add $1, %[tmp]; mov %[ss], %%ss; into"
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: [tmp] "+r" (nr) : [ss] "m" (ss));
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#endif
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if (sigsetjmp(jmpbuf, 1) == 0) {
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printf("[RUN]\tMOV SS; ICEBP\n");
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/* Some emulators (e.g. QEMU TCG) don't emulate ICEBP. */
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sethandler(SIGILL, handle_and_longjmp, SA_RESETHAND);
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asm volatile ("mov %[ss], %%ss; .byte 0xf1" :: [ss] "m" (ss));
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}
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if (sigsetjmp(jmpbuf, 1) == 0) {
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printf("[RUN]\tMOV SS; CLI\n");
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sethandler(SIGSEGV, handle_and_longjmp, SA_RESETHAND);
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asm volatile ("mov %[ss], %%ss; cli" :: [ss] "m" (ss));
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}
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if (sigsetjmp(jmpbuf, 1) == 0) {
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printf("[RUN]\tMOV SS; #PF\n");
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sethandler(SIGSEGV, handle_and_longjmp, SA_RESETHAND);
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asm volatile ("mov %[ss], %%ss; mov (-1), %[tmp]"
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: [tmp] "=r" (nr) : [ss] "m" (ss));
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}
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/*
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* INT $1: if #DB has DPL=3 and there isn't special handling,
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* then the kernel will die.
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*/
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if (sigsetjmp(jmpbuf, 1) == 0) {
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printf("[RUN]\tMOV SS; INT 1\n");
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sethandler(SIGSEGV, handle_and_longjmp, SA_RESETHAND);
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asm volatile ("mov %[ss], %%ss; int $1" :: [ss] "m" (ss));
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}
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#ifdef __x86_64__
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/*
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* In principle, we should test 32-bit SYSCALL as well, but
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* the calling convention is so unpredictable that it's
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* not obviously worth the effort.
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*/
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if (sigsetjmp(jmpbuf, 1) == 0) {
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printf("[RUN]\tMOV SS; SYSCALL\n");
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sethandler(SIGILL, handle_and_longjmp, SA_RESETHAND);
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nr = SYS_getpid;
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/*
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* Toggle the high bit of RSP to make it noncanonical to
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* strengthen this test on non-SMAP systems.
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*/
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asm volatile ("btc $63, %%rsp\n\t"
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"mov %[ss], %%ss; syscall\n\t"
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"btc $63, %%rsp"
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: "+a" (nr) : [ss] "m" (ss)
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: "rcx"
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#ifdef __x86_64__
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, "r11"
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#endif
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);
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}
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#endif
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printf("[RUN]\tMOV SS; breakpointed NOP\n");
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asm volatile ("mov %[ss], %%ss; breakpoint_insn: nop" :: [ss] "m" (ss));
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/*
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* Invoking SYSENTER directly breaks all the rules. Just handle
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* the SIGSEGV.
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*/
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if (sigsetjmp(jmpbuf, 1) == 0) {
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printf("[RUN]\tMOV SS; SYSENTER\n");
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stack_t stack = {
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.ss_sp = malloc(sizeof(char) * SIGSTKSZ),
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.ss_size = SIGSTKSZ,
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};
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if (sigaltstack(&stack, NULL) != 0)
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err(1, "sigaltstack");
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sethandler(SIGSEGV, handle_and_longjmp, SA_RESETHAND | SA_ONSTACK);
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nr = SYS_getpid;
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free(stack.ss_sp);
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/* Clear EBP first to make sure we segfault cleanly. */
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asm volatile ("xorl %%ebp, %%ebp; mov %[ss], %%ss; SYSENTER" : "+a" (nr)
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: [ss] "m" (ss) : "flags", "rcx"
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#ifdef __x86_64__
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, "r11"
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#endif
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);
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/* We're unreachable here. SYSENTER forgets RIP. */
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}
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if (sigsetjmp(jmpbuf, 1) == 0) {
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printf("[RUN]\tMOV SS; INT $0x80\n");
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sethandler(SIGSEGV, handle_and_longjmp, SA_RESETHAND);
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nr = 20; /* compat getpid */
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asm volatile ("mov %[ss], %%ss; int $0x80"
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: "+a" (nr) : [ss] "m" (ss)
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: "flags"
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#ifdef __x86_64__
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, "r8", "r9", "r10", "r11"
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#endif
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);
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}
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printf("[OK]\tI aten't dead\n");
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return 0;
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}
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