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![Andy Lutomirski](/assets/img/avatar_default.png)
Mere possession of vm86 state is strange. Make sure that nothing gets corrupted if we fork after calling vm86(). Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Brian Gerst <brgerst@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Stas Sergeev <stsp@list.ru> Link: http://lkml.kernel.org/r/08f83295460a80e41dc5e3e81ec40d6844d316f5.1446270067.git.luto@kernel.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
238 lines
5.9 KiB
C
238 lines
5.9 KiB
C
/*
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* entry_from_vm86.c - tests kernel entries from vm86 mode
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* Copyright (c) 2014-2015 Andrew Lutomirski
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*
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* This exercises a few paths that need to special-case vm86 mode.
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*
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* GPL v2.
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*/
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#define _GNU_SOURCE
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#include <assert.h>
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#include <stdlib.h>
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#include <sys/syscall.h>
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#include <sys/signal.h>
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#include <sys/ucontext.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <string.h>
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#include <inttypes.h>
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#include <sys/mman.h>
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#include <err.h>
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#include <stddef.h>
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#include <stdbool.h>
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#include <errno.h>
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#include <sys/vm86.h>
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static unsigned long load_addr = 0x10000;
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static int nerrs = 0;
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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 void clearhandler(int sig)
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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_handler = SIG_DFL;
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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 sig_atomic_t got_signal;
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static void sighandler(int sig, siginfo_t *info, void *ctx_void)
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{
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ucontext_t *ctx = (ucontext_t*)ctx_void;
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if (ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_VM ||
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(ctx->uc_mcontext.gregs[REG_CS] & 3) != 3) {
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printf("[FAIL]\tSignal frame should not reflect vm86 mode\n");
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nerrs++;
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}
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const char *signame;
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if (sig == SIGSEGV)
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signame = "SIGSEGV";
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else if (sig == SIGILL)
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signame = "SIGILL";
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else
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signame = "unexpected signal";
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printf("[INFO]\t%s: FLAGS = 0x%lx, CS = 0x%hx\n", signame,
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(unsigned long)ctx->uc_mcontext.gregs[REG_EFL],
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(unsigned short)ctx->uc_mcontext.gregs[REG_CS]);
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got_signal = 1;
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}
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asm (
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".pushsection .rodata\n\t"
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".type vmcode_bound, @object\n\t"
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"vmcode:\n\t"
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"vmcode_bound:\n\t"
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".code16\n\t"
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"bound %ax, (2048)\n\t"
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"int3\n\t"
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"vmcode_sysenter:\n\t"
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"sysenter\n\t"
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"vmcode_syscall:\n\t"
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"syscall\n\t"
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"vmcode_sti:\n\t"
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"sti\n\t"
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"vmcode_int3:\n\t"
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"int3\n\t"
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"vmcode_int80:\n\t"
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"int $0x80\n\t"
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".size vmcode, . - vmcode\n\t"
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"end_vmcode:\n\t"
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".code32\n\t"
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".popsection"
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);
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extern unsigned char vmcode[], end_vmcode[];
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extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
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vmcode_sti[], vmcode_int3[], vmcode_int80[];
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/* Returns false if the test was skipped. */
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static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
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unsigned int rettype, unsigned int retarg,
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const char *text)
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{
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long ret;
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printf("[RUN]\t%s from vm86 mode\n", text);
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v86->regs.eip = eip;
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ret = vm86(VM86_ENTER, v86);
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if (ret == -1 && (errno == ENOSYS || errno == EPERM)) {
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printf("[SKIP]\tvm86 %s\n",
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errno == ENOSYS ? "not supported" : "not allowed");
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return false;
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}
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if (VM86_TYPE(ret) == VM86_INTx) {
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char trapname[32];
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int trapno = VM86_ARG(ret);
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if (trapno == 13)
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strcpy(trapname, "GP");
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else if (trapno == 5)
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strcpy(trapname, "BR");
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else if (trapno == 14)
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strcpy(trapname, "PF");
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else
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sprintf(trapname, "%d", trapno);
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printf("[INFO]\tExited vm86 mode due to #%s\n", trapname);
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} else if (VM86_TYPE(ret) == VM86_UNKNOWN) {
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printf("[INFO]\tExited vm86 mode due to unhandled GP fault\n");
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} else if (VM86_TYPE(ret) == VM86_TRAP) {
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printf("[INFO]\tExited vm86 mode due to a trap (arg=%ld)\n",
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VM86_ARG(ret));
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} else if (VM86_TYPE(ret) == VM86_SIGNAL) {
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printf("[INFO]\tExited vm86 mode due to a signal\n");
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} else if (VM86_TYPE(ret) == VM86_STI) {
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printf("[INFO]\tExited vm86 mode due to STI\n");
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} else {
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printf("[INFO]\tExited vm86 mode due to type %ld, arg %ld\n",
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VM86_TYPE(ret), VM86_ARG(ret));
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}
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if (rettype == -1 ||
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(VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) {
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printf("[OK]\tReturned correctly\n");
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} else {
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printf("[FAIL]\tIncorrect return reason\n");
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nerrs++;
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}
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return true;
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}
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int main(void)
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{
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struct vm86plus_struct v86;
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unsigned char *addr = mmap((void *)load_addr, 4096,
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PROT_READ | PROT_WRITE | PROT_EXEC,
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MAP_ANONYMOUS | MAP_PRIVATE, -1,0);
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if (addr != (unsigned char *)load_addr)
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err(1, "mmap");
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memcpy(addr, vmcode, end_vmcode - vmcode);
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addr[2048] = 2;
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addr[2050] = 3;
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memset(&v86, 0, sizeof(v86));
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v86.regs.cs = load_addr / 16;
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v86.regs.ss = load_addr / 16;
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v86.regs.ds = load_addr / 16;
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v86.regs.es = load_addr / 16;
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assert((v86.regs.cs & 3) == 0); /* Looks like RPL = 0 */
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/* #BR -- should deliver SIG??? */
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do_test(&v86, vmcode_bound - vmcode, VM86_INTx, 5, "#BR");
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/*
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* SYSENTER -- should cause #GP or #UD depending on CPU.
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* Expected return type -1 means that we shouldn't validate
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* the vm86 return value. This will avoid problems on non-SEP
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* CPUs.
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*/
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sethandler(SIGILL, sighandler, 0);
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do_test(&v86, vmcode_sysenter - vmcode, -1, 0, "SYSENTER");
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clearhandler(SIGILL);
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/*
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* SYSCALL would be a disaster in VM86 mode. Fortunately,
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* there is no kernel that both enables SYSCALL and sets
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* EFER.SCE, so it's #UD on all systems. But vm86 is
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* buggy (or has a "feature"), so the SIGILL will actually
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* be delivered.
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*/
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sethandler(SIGILL, sighandler, 0);
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do_test(&v86, vmcode_syscall - vmcode, VM86_SIGNAL, 0, "SYSCALL");
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clearhandler(SIGILL);
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/* STI with VIP set */
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v86.regs.eflags |= X86_EFLAGS_VIP;
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v86.regs.eflags &= ~X86_EFLAGS_IF;
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do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set");
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/* INT3 -- should cause #BP */
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do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3");
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/* INT80 -- should exit with "INTx 0x80" */
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v86.regs.eax = (unsigned int)-1;
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do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80");
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/* Execute a null pointer */
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v86.regs.cs = 0;
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v86.regs.ss = 0;
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sethandler(SIGSEGV, sighandler, 0);
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got_signal = 0;
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if (do_test(&v86, 0, VM86_SIGNAL, 0, "Execute null pointer") &&
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!got_signal) {
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printf("[FAIL]\tDid not receive SIGSEGV\n");
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nerrs++;
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}
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clearhandler(SIGSEGV);
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/* Make sure nothing explodes if we fork. */
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if (fork() > 0)
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return 0;
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return (nerrs == 0 ? 0 : 1);
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}
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