bf6465d046
Linux CET kernel places a restore token on shadow stack for signal handler to enhance security. The restore token is 8 byte and aligned to 8 bytes. It is usually transparent to user programs since kernel will pop the restore token when signal handler returns. But when an exception is thrown from a signal handler, now we need to pop the restore token from shadow stack. For x86-64, we just need to treat the signal frame as normal frame. For i386, we need to search for the restore token to check if the original shadow stack is 8 byte aligned. If the original shadow stack is 8 byte aligned, we just need to pop 2 slots, one restore token, from shadow stack. Otherwise, we need to pop 3 slots, one restore token + 4 byte padding, from shadow stack. This patch also includes 2 tests, one has a restore token with 4 byte padding and one without. Tested on Linux/x86-64 CET machine with and without -m32. libgcc/ PR libgcc/85334 * config/i386/shadow-stack-unwind.h (_Unwind_Frames_Increment): New. gcc/testsuite/ PR libgcc/85334 * g++.target/i386/pr85334-1.C: New test. * g++.target/i386/pr85334-2.C: Likewise.
95 lines
3.3 KiB
C
95 lines
3.3 KiB
C
/* _Unwind_Frames_Extra with shadow stack for x86-64 and x86.
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Copyright (C) 2017-2020 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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GCC is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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/* NB: We need _get_ssp and _inc_ssp from <cetintrin.h>. But we can't
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include <x86intrin.h> which ends up including <mm_malloc.h>, which
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includes <stdlib.h> and <errno.h> unconditionally. But we can't
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include any libc system headers unconditionally from libgcc. Avoid
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including <mm_malloc.h> here by defining _IMMINTRIN_H_INCLUDED. */
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#define _IMMINTRIN_H_INCLUDED
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#include <cetintrin.h>
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#undef _IMMINTRIN_H_INCLUDED
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/* Unwind the shadow stack for EH. */
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#undef _Unwind_Frames_Extra
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#define _Unwind_Frames_Extra(x) \
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do \
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{ \
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_Unwind_Word ssp = _get_ssp (); \
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if (ssp != 0) \
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{ \
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_Unwind_Word tmp = (x); \
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while (tmp > 255) \
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{ \
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_inc_ssp (255); \
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tmp -= 255; \
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} \
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_inc_ssp (tmp); \
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} \
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} \
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while (0)
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/* Linux CET kernel places a restore token on shadow stack for signal
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handler to enhance security. The restore token is 8 byte and aligned
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to 8 bytes. It is usually transparent to user programs since kernel
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will pop the restore token when signal handler returns. But when an
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exception is thrown from a signal handler, now we need to pop the
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restore token from shadow stack. For x86-64, we just need to treat
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the signal frame as normal frame. For i386, we need to search for
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the restore token to check if the original shadow stack is 8 byte
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aligned. If the original shadow stack is 8 byte aligned, we just
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need to pop 2 slots, one restore token, from shadow stack. Otherwise,
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we need to pop 3 slots, one restore token + 4 byte padding, from
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shadow stack. */
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#ifndef __x86_64__
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#undef _Unwind_Frames_Increment
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#define _Unwind_Frames_Increment(context, frames) \
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if (_Unwind_IsSignalFrame (context)) \
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do \
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{ \
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_Unwind_Word ssp, prev_ssp, token; \
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ssp = _get_ssp (); \
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if (ssp != 0) \
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{ \
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/* Align shadow stack pointer to the next \
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8 byte aligned boundary. */ \
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ssp = (ssp + 4) & ~7; \
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do \
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{ \
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/* Look for a restore token. */ \
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token = (*(_Unwind_Word *) (ssp - 8)); \
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prev_ssp = token & ~7; \
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if (prev_ssp == ssp) \
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break; \
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ssp += 8; \
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} \
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while (1); \
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frames += (token & 0x4) ? 3 : 2; \
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} \
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} \
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while (0); \
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else \
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frames++;
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#endif
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