1 /* _Unwind_Frames_Extra with shadow stack for x86-64 and x86. 2 Copyright (C) 2017-2021 Free Software Foundation, Inc. 3 4 This file is part of GCC. 5 6 GCC is free software; you can redistribute it and/or modify 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 3, or (at your option) 9 any later version. 10 11 GCC 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 14 GNU General Public License for more details. 15 16 Under Section 7 of GPL version 3, you are granted additional 17 permissions described in the GCC Runtime Library Exception, version 18 3.1, as published by the Free Software Foundation. 19 20 You should have received a copy of the GNU General Public License and 21 a copy of the GCC Runtime Library Exception along with this program; 22 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23 <http://www.gnu.org/licenses/>. */ 24 25 #include <x86gprintrin.h> 26 27 /* Unwind the shadow stack for EH. */ 28 #undef _Unwind_Frames_Extra 29 #define _Unwind_Frames_Extra(x) \ 30 do \ 31 { \ 32 _Unwind_Word ssp = _get_ssp (); \ 33 if (ssp != 0) \ 34 { \ 35 _Unwind_Word tmp = (x); \ 36 while (tmp > 255) \ 37 { \ 38 _inc_ssp (255); \ 39 tmp -= 255; \ 40 } \ 41 _inc_ssp (tmp); \ 42 } \ 43 } \ 44 while (0) 45 46 /* Linux CET kernel places a restore token on shadow stack for signal 47 handler to enhance security. The restore token is 8 byte and aligned 48 to 8 bytes. It is usually transparent to user programs since kernel 49 will pop the restore token when signal handler returns. But when an 50 exception is thrown from a signal handler, now we need to pop the 51 restore token from shadow stack. For x86-64, we just need to treat 52 the signal frame as normal frame. For i386, we need to search for 53 the restore token to check if the original shadow stack is 8 byte 54 aligned. If the original shadow stack is 8 byte aligned, we just 55 need to pop 2 slots, one restore token, from shadow stack. Otherwise, 56 we need to pop 3 slots, one restore token + 4 byte padding, from 57 shadow stack. */ 58 #ifndef __x86_64__ 59 #undef _Unwind_Frames_Increment 60 #define _Unwind_Frames_Increment(context, frames) \ 61 if (_Unwind_IsSignalFrame (context)) \ 62 do \ 63 { \ 64 _Unwind_Word ssp, prev_ssp, token; \ 65 ssp = _get_ssp (); \ 66 if (ssp != 0) \ 67 { \ 68 /* Align shadow stack pointer to the next \ 69 8 byte aligned boundary. */ \ 70 ssp = (ssp + 4) & ~7; \ 71 do \ 72 { \ 73 /* Look for a restore token. */ \ 74 token = (*(_Unwind_Word *) (ssp - 8)); \ 75 prev_ssp = token & ~7; \ 76 if (prev_ssp == ssp) \ 77 break; \ 78 ssp += 8; \ 79 } \ 80 while (1); \ 81 frames += (token & 0x4) ? 3 : 2; \ 82 } \ 83 } \ 84 while (0); \ 85 else \ 86 frames++; 87 #endif 88