1 /* 2 * This file and its contents are supplied under the terms of the 3 * Common Development and Distribution License ("CDDL"), version 1.0. 4 * You may only use this file in accordance with the terms of version 5 * 1.0 of the CDDL. 6 * 7 * A full copy of the text of the CDDL should have accompanied this 8 * source. A copy of the CDDL is also available via the Internet at 9 * http://www.illumos.org/license/CDDL. 10 */ 11 12 /* 13 * Copyright 2020 Oxide Computer Company 14 */ 15 16 #include <upanic.h> 17 #include <sys/random.h> 18 19 /* 20 * This provides an implementation of the stack protector functions that are 21 * expected by gcc's ssp implementation. 22 * 23 * We attempt to initialize the stack guard with random data, which is our best 24 * protection. If that fails, we'd like to have a guard that is still meaningful 25 * and not totally predictable. The original StackGuard paper suggests using a 26 * terminator canary. To make this a little more difficult, we also use a 27 * portion of the data from gethrtime(). 28 * 29 * In a 32-bit environment, we only have four bytes worth of data. We use the 30 * lower two bytes of the gethrtime() value and then use pieces of the 31 * terminator canary, '\n\0'. In a 64-bit environment we use the full four byte 32 * terminator canary and then four bytes of gethrtime. 33 */ 34 35 /* 36 * Use an array here so it's easier to get the length at compile time. 37 */ 38 static const char ssp_msg[] = "*** stack smashing detected"; 39 40 uintptr_t __stack_chk_guard; 41 42 void 43 ssp_init(void) 44 { 45 if (getrandom(&__stack_chk_guard, sizeof (__stack_chk_guard), 0) != 46 sizeof (__stack_chk_guard)) { 47 /* 48 * This failed, attempt to get some data that might let us get 49 * off the ground. 50 */ 51 hrtime_t t = gethrtime(); 52 #ifdef _LP32 53 const uint16_t guard = '\n' << 8 | '\0'; 54 __stack_chk_guard = guard << 16 | (uint16_t)t; 55 #else 56 const uint32_t guard = '\r' << 24 | '\n' << 16 | '\0' << 8 | 57 '\xff'; 58 __stack_chk_guard = (uint64_t)guard << 32 | (uint32_t)t; 59 #endif 60 } 61 } 62 63 void 64 __stack_chk_fail(void) 65 { 66 upanic(ssp_msg, sizeof (ssp_msg)); 67 } 68