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- /*
- * entry_from_vm86.c - tests kernel entries from vm86 mode
- * Copyright (c) 2014-2015 Andrew Lutomirski
- *
- * This exercises a few paths that need to special-case vm86 mode.
- *
- * GPL v2.
- */
- #define _GNU_SOURCE
- #include <assert.h>
- #include <stdlib.h>
- #include <sys/syscall.h>
- #include <sys/signal.h>
- #include <sys/ucontext.h>
- #include <unistd.h>
- #include <stdio.h>
- #include <string.h>
- #include <inttypes.h>
- #include <sys/mman.h>
- #include <err.h>
- #include <stddef.h>
- #include <stdbool.h>
- #include <errno.h>
- #include <sys/vm86.h>
- static unsigned long load_addr = 0x10000;
- static int nerrs = 0;
- static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
- int flags)
- {
- struct sigaction sa;
- memset(&sa, 0, sizeof(sa));
- sa.sa_sigaction = handler;
- sa.sa_flags = SA_SIGINFO | flags;
- sigemptyset(&sa.sa_mask);
- if (sigaction(sig, &sa, 0))
- err(1, "sigaction");
- }
- static void clearhandler(int sig)
- {
- struct sigaction sa;
- memset(&sa, 0, sizeof(sa));
- sa.sa_handler = SIG_DFL;
- sigemptyset(&sa.sa_mask);
- if (sigaction(sig, &sa, 0))
- err(1, "sigaction");
- }
- static sig_atomic_t got_signal;
- static void sighandler(int sig, siginfo_t *info, void *ctx_void)
- {
- ucontext_t *ctx = (ucontext_t*)ctx_void;
- if (ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_VM ||
- (ctx->uc_mcontext.gregs[REG_CS] & 3) != 3) {
- printf("[FAIL]\tSignal frame should not reflect vm86 mode\n");
- nerrs++;
- }
- const char *signame;
- if (sig == SIGSEGV)
- signame = "SIGSEGV";
- else if (sig == SIGILL)
- signame = "SIGILL";
- else
- signame = "unexpected signal";
- printf("[INFO]\t%s: FLAGS = 0x%lx, CS = 0x%hx\n", signame,
- (unsigned long)ctx->uc_mcontext.gregs[REG_EFL],
- (unsigned short)ctx->uc_mcontext.gregs[REG_CS]);
- got_signal = 1;
- }
- asm (
- ".pushsection .rodata\n\t"
- ".type vmcode_bound, @object\n\t"
- "vmcode:\n\t"
- "vmcode_bound:\n\t"
- ".code16\n\t"
- "bound %ax, (2048)\n\t"
- "int3\n\t"
- "vmcode_sysenter:\n\t"
- "sysenter\n\t"
- "vmcode_syscall:\n\t"
- "syscall\n\t"
- "vmcode_sti:\n\t"
- "sti\n\t"
- "vmcode_int3:\n\t"
- "int3\n\t"
- "vmcode_int80:\n\t"
- "int $0x80\n\t"
- "vmcode_popf_hlt:\n\t"
- "push %ax\n\t"
- "popf\n\t"
- "hlt\n\t"
- "vmcode_umip:\n\t"
- /* addressing via displacements */
- "smsw (2052)\n\t"
- "sidt (2054)\n\t"
- "sgdt (2060)\n\t"
- /* addressing via registers */
- "mov $2066, %bx\n\t"
- "smsw (%bx)\n\t"
- "mov $2068, %bx\n\t"
- "sidt (%bx)\n\t"
- "mov $2074, %bx\n\t"
- "sgdt (%bx)\n\t"
- /* register operands, only for smsw */
- "smsw %ax\n\t"
- "mov %ax, (2080)\n\t"
- "int3\n\t"
- "vmcode_umip_str:\n\t"
- "str %eax\n\t"
- "vmcode_umip_sldt:\n\t"
- "sldt %eax\n\t"
- "int3\n\t"
- ".size vmcode, . - vmcode\n\t"
- "end_vmcode:\n\t"
- ".code32\n\t"
- ".popsection"
- );
- extern unsigned char vmcode[], end_vmcode[];
- extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
- vmcode_sti[], vmcode_int3[], vmcode_int80[], vmcode_popf_hlt[],
- vmcode_umip[], vmcode_umip_str[], vmcode_umip_sldt[];
- /* Returns false if the test was skipped. */
- static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
- unsigned int rettype, unsigned int retarg,
- const char *text)
- {
- long ret;
- printf("[RUN]\t%s from vm86 mode\n", text);
- v86->regs.eip = eip;
- ret = vm86(VM86_ENTER, v86);
- if (ret == -1 && (errno == ENOSYS || errno == EPERM)) {
- printf("[SKIP]\tvm86 %s\n",
- errno == ENOSYS ? "not supported" : "not allowed");
- return false;
- }
- if (VM86_TYPE(ret) == VM86_INTx) {
- char trapname[32];
- int trapno = VM86_ARG(ret);
- if (trapno == 13)
- strcpy(trapname, "GP");
- else if (trapno == 5)
- strcpy(trapname, "BR");
- else if (trapno == 14)
- strcpy(trapname, "PF");
- else
- sprintf(trapname, "%d", trapno);
- printf("[INFO]\tExited vm86 mode due to #%s\n", trapname);
- } else if (VM86_TYPE(ret) == VM86_UNKNOWN) {
- printf("[INFO]\tExited vm86 mode due to unhandled GP fault\n");
- } else if (VM86_TYPE(ret) == VM86_TRAP) {
- printf("[INFO]\tExited vm86 mode due to a trap (arg=%ld)\n",
- VM86_ARG(ret));
- } else if (VM86_TYPE(ret) == VM86_SIGNAL) {
- printf("[INFO]\tExited vm86 mode due to a signal\n");
- } else if (VM86_TYPE(ret) == VM86_STI) {
- printf("[INFO]\tExited vm86 mode due to STI\n");
- } else {
- printf("[INFO]\tExited vm86 mode due to type %ld, arg %ld\n",
- VM86_TYPE(ret), VM86_ARG(ret));
- }
- if (rettype == -1 ||
- (VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) {
- printf("[OK]\tReturned correctly\n");
- } else {
- printf("[FAIL]\tIncorrect return reason (started at eip = 0x%lx, ended at eip = 0x%lx)\n", eip, v86->regs.eip);
- nerrs++;
- }
- return true;
- }
- void do_umip_tests(struct vm86plus_struct *vm86, unsigned char *test_mem)
- {
- struct table_desc {
- unsigned short limit;
- unsigned long base;
- } __attribute__((packed));
- /* Initialize variables with arbitrary values */
- struct table_desc gdt1 = { .base = 0x3c3c3c3c, .limit = 0x9999 };
- struct table_desc gdt2 = { .base = 0x1a1a1a1a, .limit = 0xaeae };
- struct table_desc idt1 = { .base = 0x7b7b7b7b, .limit = 0xf1f1 };
- struct table_desc idt2 = { .base = 0x89898989, .limit = 0x1313 };
- unsigned short msw1 = 0x1414, msw2 = 0x2525, msw3 = 3737;
- /* UMIP -- exit with INT3 unless kernel emulation did not trap #GP */
- do_test(vm86, vmcode_umip - vmcode, VM86_TRAP, 3, "UMIP tests");
- /* Results from displacement-only addressing */
- msw1 = *(unsigned short *)(test_mem + 2052);
- memcpy(&idt1, test_mem + 2054, sizeof(idt1));
- memcpy(&gdt1, test_mem + 2060, sizeof(gdt1));
- /* Results from register-indirect addressing */
- msw2 = *(unsigned short *)(test_mem + 2066);
- memcpy(&idt2, test_mem + 2068, sizeof(idt2));
- memcpy(&gdt2, test_mem + 2074, sizeof(gdt2));
- /* Results when using register operands */
- msw3 = *(unsigned short *)(test_mem + 2080);
- printf("[INFO]\tResult from SMSW:[0x%04x]\n", msw1);
- printf("[INFO]\tResult from SIDT: limit[0x%04x]base[0x%08lx]\n",
- idt1.limit, idt1.base);
- printf("[INFO]\tResult from SGDT: limit[0x%04x]base[0x%08lx]\n",
- gdt1.limit, gdt1.base);
- if (msw1 != msw2 || msw1 != msw3)
- printf("[FAIL]\tAll the results of SMSW should be the same.\n");
- else
- printf("[PASS]\tAll the results from SMSW are identical.\n");
- if (memcmp(&gdt1, &gdt2, sizeof(gdt1)))
- printf("[FAIL]\tAll the results of SGDT should be the same.\n");
- else
- printf("[PASS]\tAll the results from SGDT are identical.\n");
- if (memcmp(&idt1, &idt2, sizeof(idt1)))
- printf("[FAIL]\tAll the results of SIDT should be the same.\n");
- else
- printf("[PASS]\tAll the results from SIDT are identical.\n");
- sethandler(SIGILL, sighandler, 0);
- do_test(vm86, vmcode_umip_str - vmcode, VM86_SIGNAL, 0,
- "STR instruction");
- clearhandler(SIGILL);
- sethandler(SIGILL, sighandler, 0);
- do_test(vm86, vmcode_umip_sldt - vmcode, VM86_SIGNAL, 0,
- "SLDT instruction");
- clearhandler(SIGILL);
- }
- int main(void)
- {
- struct vm86plus_struct v86;
- unsigned char *addr = mmap((void *)load_addr, 4096,
- PROT_READ | PROT_WRITE | PROT_EXEC,
- MAP_ANONYMOUS | MAP_PRIVATE, -1,0);
- if (addr != (unsigned char *)load_addr)
- err(1, "mmap");
- memcpy(addr, vmcode, end_vmcode - vmcode);
- addr[2048] = 2;
- addr[2050] = 3;
- memset(&v86, 0, sizeof(v86));
- v86.regs.cs = load_addr / 16;
- v86.regs.ss = load_addr / 16;
- v86.regs.ds = load_addr / 16;
- v86.regs.es = load_addr / 16;
- /* Use the end of the page as our stack. */
- v86.regs.esp = 4096;
- assert((v86.regs.cs & 3) == 0); /* Looks like RPL = 0 */
- /* #BR -- should deliver SIG??? */
- do_test(&v86, vmcode_bound - vmcode, VM86_INTx, 5, "#BR");
- /*
- * SYSENTER -- should cause #GP or #UD depending on CPU.
- * Expected return type -1 means that we shouldn't validate
- * the vm86 return value. This will avoid problems on non-SEP
- * CPUs.
- */
- sethandler(SIGILL, sighandler, 0);
- do_test(&v86, vmcode_sysenter - vmcode, -1, 0, "SYSENTER");
- clearhandler(SIGILL);
- /*
- * SYSCALL would be a disaster in VM86 mode. Fortunately,
- * there is no kernel that both enables SYSCALL and sets
- * EFER.SCE, so it's #UD on all systems. But vm86 is
- * buggy (or has a "feature"), so the SIGILL will actually
- * be delivered.
- */
- sethandler(SIGILL, sighandler, 0);
- do_test(&v86, vmcode_syscall - vmcode, VM86_SIGNAL, 0, "SYSCALL");
- clearhandler(SIGILL);
- /* STI with VIP set */
- v86.regs.eflags |= X86_EFLAGS_VIP;
- v86.regs.eflags &= ~X86_EFLAGS_IF;
- do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set");
- /* POPF with VIP set but IF clear: should not trap */
- v86.regs.eflags = X86_EFLAGS_VIP;
- v86.regs.eax = 0;
- do_test(&v86, vmcode_popf_hlt - vmcode, VM86_UNKNOWN, 0, "POPF with VIP set and IF clear");
- /* POPF with VIP set and IF set: should trap */
- v86.regs.eflags = X86_EFLAGS_VIP;
- v86.regs.eax = X86_EFLAGS_IF;
- do_test(&v86, vmcode_popf_hlt - vmcode, VM86_STI, 0, "POPF with VIP and IF set");
- /* POPF with VIP clear and IF set: should not trap */
- v86.regs.eflags = 0;
- v86.regs.eax = X86_EFLAGS_IF;
- do_test(&v86, vmcode_popf_hlt - vmcode, VM86_UNKNOWN, 0, "POPF with VIP clear and IF set");
- v86.regs.eflags = 0;
- /* INT3 -- should cause #BP */
- do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3");
- /* INT80 -- should exit with "INTx 0x80" */
- v86.regs.eax = (unsigned int)-1;
- do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80");
- /* UMIP -- should exit with INTx 0x80 unless UMIP was not disabled */
- do_umip_tests(&v86, addr);
- /* Execute a null pointer */
- v86.regs.cs = 0;
- v86.regs.ss = 0;
- sethandler(SIGSEGV, sighandler, 0);
- got_signal = 0;
- if (do_test(&v86, 0, VM86_SIGNAL, 0, "Execute null pointer") &&
- !got_signal) {
- printf("[FAIL]\tDid not receive SIGSEGV\n");
- nerrs++;
- }
- clearhandler(SIGSEGV);
- /* Make sure nothing explodes if we fork. */
- if (fork() == 0)
- return 0;
- return (nerrs == 0 ? 0 : 1);
- }
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