1 /* Check getcontext and setcontext on the context from makecontext
2    with shadow stack.
3    Copyright (C) 2018-2021 Free Software Foundation, Inc.
4    This file is part of the GNU C Library.
5 
6    The GNU C Library is free software; you can redistribute it and/or
7    modify it under the terms of the GNU Lesser General Public
8    License as published by the Free Software Foundation; either
9    version 2.1 of the License, or (at your option) any later version.
10 
11    The GNU C Library is distributed in the hope that it will be useful,
12    but WITHOUT ANY WARRANTY; without even the implied warranty of
13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
14    Lesser General Public License for more details.
15 
16    You should have received a copy of the GNU Lesser General Public
17    License along with the GNU C Library; if not, see
18    <https://www.gnu.org/licenses/>.  */
19 
20 #include <stdio.h>
21 #include <stdint.h>
22 #include <stdlib.h>
23 #include <ucontext.h>
24 #include <unistd.h>
25 #include <sys/mman.h>
26 #include <stdatomic.h>
27 #include <x86intrin.h>
28 
29 static ucontext_t ctx[5];
30 static atomic_int done;
31 
32 static void
33 __attribute__((noinline, noclone))
f2(void)34 f2 (void)
35 {
36   printf ("start f2\n");
37   done++;
38   if (setcontext (&ctx[2]) != 0)
39     {
40       printf ("%s: setcontext: %m\n", __FUNCTION__);
41       exit (EXIT_FAILURE);
42     }
43 }
44 
45 static void
f1(void)46 f1 (void)
47 {
48   printf ("start f1\n");
49   if (getcontext (&ctx[2]) != 0)
50     {
51       printf ("%s: getcontext: %m\n", __FUNCTION__);
52       exit (EXIT_FAILURE);
53     }
54   if (done)
55     exit (EXIT_SUCCESS);
56   f2 ();
57 }
58 
59 static int
do_test(void)60 do_test (void)
61 {
62   char st1[32768];
63   puts ("making contexts");
64   if (getcontext (&ctx[0]) != 0)
65     {
66       printf ("%s: getcontext: %m\n", __FUNCTION__);
67       exit (EXIT_FAILURE);
68     }
69   if (getcontext (&ctx[1]) != 0)
70     {
71       printf ("%s: getcontext: %m\n", __FUNCTION__);
72       exit (EXIT_FAILURE);
73     }
74 
75   ctx[3].uc_stack.ss_sp = st1;
76   ctx[3].uc_stack.ss_size = sizeof st1;
77   ctx[3].uc_link = &ctx[0];
78   makecontext (&ctx[3], (void (*) (void)) f1, 0);
79 
80   ctx[1].uc_stack.ss_sp = st1;
81   ctx[1].uc_stack.ss_size = sizeof st1;
82   ctx[1].uc_link = &ctx[0];
83   makecontext (&ctx[1], (void (*) (void)) f1, 0);
84 
85   ctx[4].uc_stack.ss_sp = st1;
86   ctx[4].uc_stack.ss_size = sizeof st1;
87   ctx[4].uc_link = &ctx[0];
88   makecontext (&ctx[4], (void (*) (void)) f1, 0);
89 
90   /* NB: When shadow stack is enabled, makecontext calls arch_prctl
91      with ARCH_CET_ALLOC_SHSTK to allocate a new shadow stack which
92      can be unmapped.  The base address and size of the new shadow
93      stack are returned in __ssp[1] and __ssp[2].  makecontext is
94      called for CTX1, CTX3 and CTX4.  But only CTX1 is used.  New
95      shadow stacks are allocated in the order of CTX3, CTX1, CTX4.
96      It is very likely that CTX1's shadow stack is placed between
97      CTX3 and CTX4.  We munmap CTX3's and CTX4's shadow stacks to
98      create gaps above and below CTX1's shadow stack.  We check
99      that setcontext CTX1 works correctly in this case.  */
100   if (_get_ssp () != 0)
101     {
102       if (ctx[3].__ssp[1] != 0
103 	  && munmap ((void *) (uintptr_t) ctx[3].__ssp[1],
104 		     (size_t) ctx[3].__ssp[2]) != 0)
105 	{
106 	  printf ("%s: munmap: %m\n", __FUNCTION__);
107 	  exit (EXIT_FAILURE);
108 	}
109 
110       if (ctx[4].__ssp[1] != 0
111 	  && munmap ((void *) (uintptr_t) ctx[4].__ssp[1],
112 		     (size_t) ctx[4].__ssp[2]) != 0)
113 	{
114 	  printf ("%s: munmap: %m\n", __FUNCTION__);
115 	  exit (EXIT_FAILURE);
116 	}
117     }
118 
119   if (setcontext (&ctx[1]) != 0)
120     {
121       printf ("%s: setcontext: %m\n", __FUNCTION__);
122       exit (EXIT_FAILURE);
123     }
124   exit (EXIT_FAILURE);
125 }
126 
127 #include <support/test-driver.c>
128