1/*
2 * unwind_vdso.c - tests unwind info for AT_SYSINFO in the vDSO
3 * Copyright (c) 2014-2015 Andrew Lutomirski
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms and conditions of the GNU General Public License,
7 * version 2, as published by the Free Software Foundation.
8 *
9 * This program is distributed in the hope it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
12 * General Public License for more details.
13 *
14 * This tests __kernel_vsyscall's unwind info.
15 */
16
17#define _GNU_SOURCE
18
19#include <features.h>
20#include <stdio.h>
21
22#if defined(__GLIBC__) && __GLIBC__ == 2 && __GLIBC_MINOR__ < 16
23
24int main()
25{
26	/* We need getauxval(). */
27	printf("[SKIP]\tGLIBC before 2.16 cannot compile this test\n");
28	return 0;
29}
30
31#else
32
33#include <sys/time.h>
34#include <stdlib.h>
35#include <syscall.h>
36#include <unistd.h>
37#include <string.h>
38#include <inttypes.h>
39#include <sys/mman.h>
40#include <signal.h>
41#include <sys/ucontext.h>
42#include <err.h>
43#include <stddef.h>
44#include <stdbool.h>
45#include <sys/ptrace.h>
46#include <sys/user.h>
47#include <sys/ucontext.h>
48#include <link.h>
49#include <sys/auxv.h>
50#include <dlfcn.h>
51#include <unwind.h>
52
53static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
54		       int flags)
55{
56	struct sigaction sa;
57	memset(&sa, 0, sizeof(sa));
58	sa.sa_sigaction = handler;
59	sa.sa_flags = SA_SIGINFO | flags;
60	sigemptyset(&sa.sa_mask);
61	if (sigaction(sig, &sa, 0))
62		err(1, "sigaction");
63}
64
65#ifdef __x86_64__
66# define WIDTH "q"
67#else
68# define WIDTH "l"
69#endif
70
71static unsigned long get_eflags(void)
72{
73	unsigned long eflags;
74	asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
75	return eflags;
76}
77
78static void set_eflags(unsigned long eflags)
79{
80	asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
81		      : : "rm" (eflags) : "flags");
82}
83
84#define X86_EFLAGS_TF (1UL << 8)
85
86static volatile sig_atomic_t nerrs;
87static unsigned long sysinfo;
88static bool got_sysinfo = false;
89static unsigned long return_address;
90
91struct unwind_state {
92	unsigned long ip;	/* trap source */
93	int depth;		/* -1 until we hit the trap source */
94};
95
96_Unwind_Reason_Code trace_fn(struct _Unwind_Context * ctx, void *opaque)
97{
98	struct unwind_state *state = opaque;
99	unsigned long ip = _Unwind_GetIP(ctx);
100
101	if (state->depth == -1) {
102		if (ip == state->ip)
103			state->depth = 0;
104		else
105			return _URC_NO_REASON;	/* Not there yet */
106	}
107	printf("\t  0x%lx\n", ip);
108
109	if (ip == return_address) {
110		/* Here we are. */
111		unsigned long eax = _Unwind_GetGR(ctx, 0);
112		unsigned long ecx = _Unwind_GetGR(ctx, 1);
113		unsigned long edx = _Unwind_GetGR(ctx, 2);
114		unsigned long ebx = _Unwind_GetGR(ctx, 3);
115		unsigned long ebp = _Unwind_GetGR(ctx, 5);
116		unsigned long esi = _Unwind_GetGR(ctx, 6);
117		unsigned long edi = _Unwind_GetGR(ctx, 7);
118		bool ok = (eax == SYS_getpid || eax == getpid()) &&
119			ebx == 1 && ecx == 2 && edx == 3 &&
120			esi == 4 && edi == 5 && ebp == 6;
121
122		if (!ok)
123			nerrs++;
124		printf("[%s]\t  NR = %ld, args = %ld, %ld, %ld, %ld, %ld, %ld\n",
125		       (ok ? "OK" : "FAIL"),
126		       eax, ebx, ecx, edx, esi, edi, ebp);
127
128		return _URC_NORMAL_STOP;
129	} else {
130		state->depth++;
131		return _URC_NO_REASON;
132	}
133}
134
135static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
136{
137	ucontext_t *ctx = (ucontext_t *)ctx_void;
138	struct unwind_state state;
139	unsigned long ip = ctx->uc_mcontext.gregs[REG_EIP];
140
141	if (!got_sysinfo && ip == sysinfo) {
142		got_sysinfo = true;
143
144		/* Find the return address. */
145		return_address = *(unsigned long *)(unsigned long)ctx->uc_mcontext.gregs[REG_ESP];
146
147		printf("\tIn vsyscall at 0x%lx, returning to 0x%lx\n",
148		       ip, return_address);
149	}
150
151	if (!got_sysinfo)
152		return;		/* Not there yet */
153
154	if (ip == return_address) {
155		ctx->uc_mcontext.gregs[REG_EFL] &= ~X86_EFLAGS_TF;
156		printf("\tVsyscall is done\n");
157		return;
158	}
159
160	printf("\tSIGTRAP at 0x%lx\n", ip);
161
162	state.ip = ip;
163	state.depth = -1;
164	_Unwind_Backtrace(trace_fn, &state);
165}
166
167int main()
168{
169	sysinfo = getauxval(AT_SYSINFO);
170	printf("\tAT_SYSINFO is 0x%lx\n", sysinfo);
171
172	Dl_info info;
173	if (!dladdr((void *)sysinfo, &info)) {
174		printf("[WARN]\tdladdr failed on AT_SYSINFO\n");
175	} else {
176		printf("[OK]\tAT_SYSINFO maps to %s, loaded at 0x%p\n",
177		       info.dli_fname, info.dli_fbase);
178	}
179
180	sethandler(SIGTRAP, sigtrap, 0);
181
182	syscall(SYS_getpid);  /* Force symbol binding without TF set. */
183	printf("[RUN]\tSet TF and check a fast syscall\n");
184	set_eflags(get_eflags() | X86_EFLAGS_TF);
185	syscall(SYS_getpid, 1, 2, 3, 4, 5, 6);
186	if (!got_sysinfo) {
187		set_eflags(get_eflags() & ~X86_EFLAGS_TF);
188
189		/*
190		 * The most likely cause of this is that you're on Debian or
191		 * a Debian-based distro, you're missing libc6-i686, and you're
192		 * affected by libc/19006 (https://sourceware.org/PR19006).
193		 */
194		printf("[WARN]\tsyscall(2) didn't enter AT_SYSINFO\n");
195	}
196
197	if (get_eflags() & X86_EFLAGS_TF) {
198		printf("[FAIL]\tTF is still set\n");
199		nerrs++;
200	}
201
202	if (nerrs) {
203		printf("[FAIL]\tThere were errors\n");
204		return 1;
205	} else {
206		printf("[OK]\tAll is well\n");
207		return 0;
208	}
209}
210
211#endif	/* New enough libc */
212