1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * syscall_arg_fault.c - tests faults 32-bit fast syscall stack args
4  * Copyright (c) 2015 Andrew Lutomirski
5  */
6 
7 #define _GNU_SOURCE
8 
9 #include <stdlib.h>
10 #include <stdio.h>
11 #include <string.h>
12 #include <sys/signal.h>
13 #include <sys/ucontext.h>
14 #include <err.h>
15 #include <setjmp.h>
16 #include <errno.h>
17 
18 #include "helpers.h"
19 
20 /* Our sigaltstack scratch space. */
21 static unsigned char altstack_data[SIGSTKSZ];
22 
23 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
24 		       int flags)
25 {
26 	struct sigaction sa;
27 	memset(&sa, 0, sizeof(sa));
28 	sa.sa_sigaction = handler;
29 	sa.sa_flags = SA_SIGINFO | flags;
30 	sigemptyset(&sa.sa_mask);
31 	if (sigaction(sig, &sa, 0))
32 		err(1, "sigaction");
33 }
34 
35 static volatile sig_atomic_t sig_traps;
36 static sigjmp_buf jmpbuf;
37 
38 static volatile sig_atomic_t n_errs;
39 
40 #ifdef __x86_64__
41 #define REG_AX REG_RAX
42 #define REG_IP REG_RIP
43 #else
44 #define REG_AX REG_EAX
45 #define REG_IP REG_EIP
46 #endif
47 
48 static void sigsegv_or_sigbus(int sig, siginfo_t *info, void *ctx_void)
49 {
50 	ucontext_t *ctx = (ucontext_t*)ctx_void;
51 	long ax = (long)ctx->uc_mcontext.gregs[REG_AX];
52 
53 	if (ax != -EFAULT && ax != -ENOSYS) {
54 		printf("[FAIL]\tAX had the wrong value: 0x%lx\n",
55 		       (unsigned long)ax);
56 		printf("\tIP = 0x%lx\n", (unsigned long)ctx->uc_mcontext.gregs[REG_IP]);
57 		n_errs++;
58 	} else {
59 		printf("[OK]\tSeems okay\n");
60 	}
61 
62 	siglongjmp(jmpbuf, 1);
63 }
64 
65 static volatile sig_atomic_t sigtrap_consecutive_syscalls;
66 
67 static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
68 {
69 	/*
70 	 * KVM has some bugs that can cause us to stop making progress.
71 	 * detect them and complain, but don't infinite loop or fail the
72 	 * test.
73 	 */
74 
75 	ucontext_t *ctx = (ucontext_t*)ctx_void;
76 	unsigned short *ip = (unsigned short *)ctx->uc_mcontext.gregs[REG_IP];
77 
78 	if (*ip == 0x340f || *ip == 0x050f) {
79 		/* The trap was on SYSCALL or SYSENTER */
80 		sigtrap_consecutive_syscalls++;
81 		if (sigtrap_consecutive_syscalls > 3) {
82 			printf("[WARN]\tGot stuck single-stepping -- you probably have a KVM bug\n");
83 			siglongjmp(jmpbuf, 1);
84 		}
85 	} else {
86 		sigtrap_consecutive_syscalls = 0;
87 	}
88 }
89 
90 static void sigill(int sig, siginfo_t *info, void *ctx_void)
91 {
92 	ucontext_t *ctx = (ucontext_t*)ctx_void;
93 	unsigned short *ip = (unsigned short *)ctx->uc_mcontext.gregs[REG_IP];
94 
95 	if (*ip == 0x0b0f) {
96 		/* one of the ud2 instructions faulted */
97 		printf("[OK]\tSYSCALL returned normally\n");
98 	} else {
99 		printf("[SKIP]\tIllegal instruction\n");
100 	}
101 	siglongjmp(jmpbuf, 1);
102 }
103 
104 int main()
105 {
106 	stack_t stack = {
107 		.ss_sp = altstack_data,
108 		.ss_size = SIGSTKSZ,
109 	};
110 	if (sigaltstack(&stack, NULL) != 0)
111 		err(1, "sigaltstack");
112 
113 	sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
114 	/*
115 	 * The actual exception can vary.  On Atom CPUs, we get #SS
116 	 * instead of #PF when the vDSO fails to access the stack when
117 	 * ESP is too close to 2^32, and #SS causes SIGBUS.
118 	 */
119 	sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK);
120 	sethandler(SIGILL, sigill, SA_ONSTACK);
121 
122 	/*
123 	 * Exercise another nasty special case.  The 32-bit SYSCALL
124 	 * and SYSENTER instructions (even in compat mode) each
125 	 * clobber one register.  A Linux system call has a syscall
126 	 * number and six arguments, and the user stack pointer
127 	 * needs to live in some register on return.  That means
128 	 * that we need eight registers, but SYSCALL and SYSENTER
129 	 * only preserve seven registers.  As a result, one argument
130 	 * ends up on the stack.  The stack is user memory, which
131 	 * means that the kernel can fail to read it.
132 	 *
133 	 * The 32-bit fast system calls don't have a defined ABI:
134 	 * we're supposed to invoke them through the vDSO.  So we'll
135 	 * fudge it: we set all regs to invalid pointer values and
136 	 * invoke the entry instruction.  The return will fail no
137 	 * matter what, and we completely lose our program state,
138 	 * but we can fix it up with a signal handler.
139 	 */
140 
141 	printf("[RUN]\tSYSENTER with invalid state\n");
142 	if (sigsetjmp(jmpbuf, 1) == 0) {
143 		asm volatile (
144 			"movl $-1, %%eax\n\t"
145 			"movl $-1, %%ebx\n\t"
146 			"movl $-1, %%ecx\n\t"
147 			"movl $-1, %%edx\n\t"
148 			"movl $-1, %%esi\n\t"
149 			"movl $-1, %%edi\n\t"
150 			"movl $-1, %%ebp\n\t"
151 			"movl $-1, %%esp\n\t"
152 			"sysenter"
153 			: : : "memory", "flags");
154 	}
155 
156 	printf("[RUN]\tSYSCALL with invalid state\n");
157 	if (sigsetjmp(jmpbuf, 1) == 0) {
158 		asm volatile (
159 			"movl $-1, %%eax\n\t"
160 			"movl $-1, %%ebx\n\t"
161 			"movl $-1, %%ecx\n\t"
162 			"movl $-1, %%edx\n\t"
163 			"movl $-1, %%esi\n\t"
164 			"movl $-1, %%edi\n\t"
165 			"movl $-1, %%ebp\n\t"
166 			"movl $-1, %%esp\n\t"
167 			"syscall\n\t"
168 			"ud2"		/* make sure we recover cleanly */
169 			: : : "memory", "flags");
170 	}
171 
172 	printf("[RUN]\tSYSENTER with TF and invalid state\n");
173 	sethandler(SIGTRAP, sigtrap, SA_ONSTACK);
174 
175 	if (sigsetjmp(jmpbuf, 1) == 0) {
176 		sigtrap_consecutive_syscalls = 0;
177 		set_eflags(get_eflags() | X86_EFLAGS_TF);
178 		asm volatile (
179 			"movl $-1, %%eax\n\t"
180 			"movl $-1, %%ebx\n\t"
181 			"movl $-1, %%ecx\n\t"
182 			"movl $-1, %%edx\n\t"
183 			"movl $-1, %%esi\n\t"
184 			"movl $-1, %%edi\n\t"
185 			"movl $-1, %%ebp\n\t"
186 			"movl $-1, %%esp\n\t"
187 			"sysenter"
188 			: : : "memory", "flags");
189 	}
190 	set_eflags(get_eflags() & ~X86_EFLAGS_TF);
191 
192 	printf("[RUN]\tSYSCALL with TF and invalid state\n");
193 	if (sigsetjmp(jmpbuf, 1) == 0) {
194 		sigtrap_consecutive_syscalls = 0;
195 		set_eflags(get_eflags() | X86_EFLAGS_TF);
196 		asm volatile (
197 			"movl $-1, %%eax\n\t"
198 			"movl $-1, %%ebx\n\t"
199 			"movl $-1, %%ecx\n\t"
200 			"movl $-1, %%edx\n\t"
201 			"movl $-1, %%esi\n\t"
202 			"movl $-1, %%edi\n\t"
203 			"movl $-1, %%ebp\n\t"
204 			"movl $-1, %%esp\n\t"
205 			"syscall\n\t"
206 			"ud2"		/* make sure we recover cleanly */
207 			: : : "memory", "flags");
208 	}
209 	set_eflags(get_eflags() & ~X86_EFLAGS_TF);
210 
211 #ifdef __x86_64__
212 	printf("[RUN]\tSYSENTER with TF, invalid state, and GSBASE < 0\n");
213 
214 	if (sigsetjmp(jmpbuf, 1) == 0) {
215 		sigtrap_consecutive_syscalls = 0;
216 
217 		asm volatile ("wrgsbase %%rax\n\t"
218 			      :: "a" (0xffffffffffff0000UL));
219 
220 		set_eflags(get_eflags() | X86_EFLAGS_TF);
221 		asm volatile (
222 			"movl $-1, %%eax\n\t"
223 			"movl $-1, %%ebx\n\t"
224 			"movl $-1, %%ecx\n\t"
225 			"movl $-1, %%edx\n\t"
226 			"movl $-1, %%esi\n\t"
227 			"movl $-1, %%edi\n\t"
228 			"movl $-1, %%ebp\n\t"
229 			"movl $-1, %%esp\n\t"
230 			"sysenter"
231 			: : : "memory", "flags");
232 	}
233 	set_eflags(get_eflags() & ~X86_EFLAGS_TF);
234 #endif
235 
236 	return 0;
237 }
238