--- /dev/null
+/*
+ * sigreturn.c - tests that x86 avoids Intel SYSRET pitfalls
+ * Copyright (c) 2014-2016 Andrew Lutomirski
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ */
+
+#define _GNU_SOURCE
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <inttypes.h>
+#include <sys/signal.h>
+#include <sys/ucontext.h>
+#include <sys/syscall.h>
+#include <err.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include <setjmp.h>
+#include <sys/user.h>
+#include <sys/mman.h>
+#include <assert.h>
+
+
+asm (
+ ".pushsection \".text\", \"ax\"\n\t"
+ ".balign 4096\n\t"
+ "test_page: .globl test_page\n\t"
+ ".fill 4094,1,0xcc\n\t"
+ "test_syscall_insn:\n\t"
+ "syscall\n\t"
+ ".ifne . - test_page - 4096\n\t"
+ ".error \"test page is not one page long\"\n\t"
+ ".endif\n\t"
+ ".popsection"
+ );
+
+extern const char test_page[];
+static void const *current_test_page_addr = test_page;
+
+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");
+}
+
+/* State used by our signal handlers. */
+static gregset_t initial_regs;
+
+static volatile unsigned long rip;
+
+static void sigsegv_for_sigreturn_test(int sig, siginfo_t *info, void *ctx_void)
+{
+ ucontext_t *ctx = (ucontext_t*)ctx_void;
+
+ if (rip != ctx->uc_mcontext.gregs[REG_RIP]) {
+ printf("[FAIL]\tRequested RIP=0x%lx but got RIP=0x%lx\n",
+ rip, (unsigned long)ctx->uc_mcontext.gregs[REG_RIP]);
+ fflush(stdout);
+ _exit(1);
+ }
+
+ memcpy(&ctx->uc_mcontext.gregs, &initial_regs, sizeof(gregset_t));
+
+ printf("[OK]\tGot SIGSEGV at RIP=0x%lx\n", rip);
+}
+
+static void sigusr1(int sig, siginfo_t *info, void *ctx_void)
+{
+ ucontext_t *ctx = (ucontext_t*)ctx_void;
+
+ memcpy(&initial_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
+
+ /* Set IP and CX to match so that SYSRET can happen. */
+ ctx->uc_mcontext.gregs[REG_RIP] = rip;
+ ctx->uc_mcontext.gregs[REG_RCX] = rip;
+
+ /* R11 and EFLAGS should already match. */
+ assert(ctx->uc_mcontext.gregs[REG_EFL] ==
+ ctx->uc_mcontext.gregs[REG_R11]);
+
+ sethandler(SIGSEGV, sigsegv_for_sigreturn_test, SA_RESETHAND);
+
+ return;
+}
+
+static void test_sigreturn_to(unsigned long ip)
+{
+ rip = ip;
+ printf("[RUN]\tsigreturn to 0x%lx\n", ip);
+ raise(SIGUSR1);
+}
+
+static jmp_buf jmpbuf;
+
+static void sigsegv_for_fallthrough(int sig, siginfo_t *info, void *ctx_void)
+{
+ ucontext_t *ctx = (ucontext_t*)ctx_void;
+
+ if (rip != ctx->uc_mcontext.gregs[REG_RIP]) {
+ printf("[FAIL]\tExpected SIGSEGV at 0x%lx but got RIP=0x%lx\n",
+ rip, (unsigned long)ctx->uc_mcontext.gregs[REG_RIP]);
+ fflush(stdout);
+ _exit(1);
+ }
+
+ siglongjmp(jmpbuf, 1);
+}
+
+static void test_syscall_fallthrough_to(unsigned long ip)
+{
+ void *new_address = (void *)(ip - 4096);
+ void *ret;
+
+ printf("[RUN]\tTrying a SYSCALL that falls through to 0x%lx\n", ip);
+
+ ret = mremap((void *)current_test_page_addr, 4096, 4096,
+ MREMAP_MAYMOVE | MREMAP_FIXED, new_address);
+ if (ret == MAP_FAILED) {
+ if (ip <= (1UL << 47) - PAGE_SIZE) {
+ err(1, "mremap to %p", new_address);
+ } else {
+ printf("[OK]\tmremap to %p failed\n", new_address);
+ return;
+ }
+ }
+
+ if (ret != new_address)
+ errx(1, "mremap malfunctioned: asked for %p but got %p\n",
+ new_address, ret);
+
+ current_test_page_addr = new_address;
+ rip = ip;
+
+ if (sigsetjmp(jmpbuf, 1) == 0) {
+ asm volatile ("call *%[syscall_insn]" :: "a" (SYS_getpid),
+ [syscall_insn] "rm" (ip - 2));
+ errx(1, "[FAIL]\tSyscall trampoline returned");
+ }
+
+ printf("[OK]\tWe survived\n");
+}
+
+int main()
+{
+ /*
+ * When the kernel returns from a slow-path syscall, it will
+ * detect whether SYSRET is appropriate. If it incorrectly
+ * thinks that SYSRET is appropriate when RIP is noncanonical,
+ * it'll crash on Intel CPUs.
+ */
+ sethandler(SIGUSR1, sigusr1, 0);
+ for (int i = 47; i < 64; i++)
+ test_sigreturn_to(1UL<<i);
+
+ clearhandler(SIGUSR1);
+
+ sethandler(SIGSEGV, sigsegv_for_fallthrough, 0);
+
+ /* One extra test to check that we didn't screw up the mremap logic. */
+ test_syscall_fallthrough_to((1UL << 47) - 2*PAGE_SIZE);
+
+ /* These are the interesting cases. */
+ for (int i = 47; i < 64; i++) {
+ test_syscall_fallthrough_to((1UL<<i) - PAGE_SIZE);
+ test_syscall_fallthrough_to(1UL<<i);
+ }
+
+ return 0;
+}
projects / platform / kernel / linux-rpi.git / commitdiff