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5d844e1b72
1. getcontext and swapcontext are updated to save the caller's shadow stack pointer and return address. 2. setcontext and swapcontext are updated to restore shadow stack and jump to new context directly. 3. makecontext is updated to allocate a new shadow stack and set the caller's return address to the helper code, L(exitcode). 4. Since we no longer save and restore EAX, ECX and EDX in getcontext, setcontext and swapcontext, we can use them as scratch register slots to enable CET in ucontext functions. Since makecontext allocates a new shadow stack when making a new context and kernel allocates a new shadow stack for clone/fork/vfork syscalls, we track the current shadow stack base. In setcontext and swapcontext, if the target shadow stack base is the same as the current shadow stack base, we unwind the shadow stack. Otherwise it is a stack switch and we look for a restore token. We enable shadow stack at run-time only if program and all used shared objects, including dlopened ones, are shadow stack enabled, which means that they must be compiled with GCC 8 or above and glibc 2.28 or above. We need to save and restore shadow stack only if shadow stack is enabled. When caller of getcontext, setcontext, swapcontext and makecontext is compiled with smaller ucontext_t, shadow stack won't be enabled at run-time. We check if shadow stack is enabled before accessing the extended field in ucontext_t. Tested on i386 CET/non-CET machines. Reviewed-by: Carlos O'Donell <carlos@redhat.com>
189 lines
4.8 KiB
ArmAsm
189 lines
4.8 KiB
ArmAsm
/* Install given context.
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Copyright (C) 2001-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2001.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library 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 GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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#include <asm/prctl.h>
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#include "ucontext_i.h"
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ENTRY(__setcontext)
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/* Load address of the context data structure. */
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movl 4(%esp), %eax
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/* Get the current signal mask. Note that we preserve EBX in case
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the system call fails and we return from the function with an
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error. */
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pushl %ebx
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cfi_adjust_cfa_offset (4)
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xorl %edx, %edx
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leal oSIGMASK(%eax), %ecx
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movl $SIG_SETMASK, %ebx
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cfi_rel_offset (ebx, 0)
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movl $__NR_sigprocmask, %eax
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ENTER_KERNEL
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popl %ebx
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cfi_adjust_cfa_offset (-4)
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cfi_restore (ebx)
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cmpl $-4095, %eax /* Check %eax for error. */
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jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */
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/* EAX was modified, reload it. */
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movl 4(%esp), %eax
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/* Restore the floating-point context. Not the registers, only the
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rest. */
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movl oFPREGS(%eax), %ecx
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fldenv (%ecx)
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/* Restore the FS segment register. We don't touch the GS register
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since it is used for threads. */
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movl oFS(%eax), %ecx
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movw %cx, %fs
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/* Load the new stack pointer. */
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cfi_def_cfa (eax, 0)
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cfi_offset (edi, oEDI)
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cfi_offset (esi, oESI)
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cfi_offset (ebp, oEBP)
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cfi_offset (ebx, oEBX)
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movl oESP(%eax), %esp
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#if SHSTK_ENABLED
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/* Check if Shadow Stack is enabled. */
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testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
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jz L(no_shstk)
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/* If the base of the target shadow stack is the same as the
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base of the current shadow stack, we unwind the shadow
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stack. Otherwise it is a stack switch and we look for a
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restore token. */
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movl oSSP(%eax), %esi
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movl %esi, %edi
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/* Get the base of the target shadow stack. */
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movl (oSSP + 4)(%eax), %ecx
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cmpl %gs:SSP_BASE_OFFSET, %ecx
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je L(unwind_shadow_stack)
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/* Align the saved original shadow stack pointer to the next
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8 byte aligned boundary. */
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andl $-8, %esi
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L(find_restore_token_loop):
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/* Look for a restore token. */
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movl -8(%esi), %ebx
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andl $-8, %ebx
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cmpl %esi, %ebx
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je L(restore_shadow_stack)
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/* Try the next slot. */
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subl $8, %esi
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jmp L(find_restore_token_loop)
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L(restore_shadow_stack):
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/* Pop return address from the shadow stack since setcontext
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will not return. */
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movl $1, %ebx
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incsspd %ebx
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/* Use the restore stoken to restore the target shadow stack. */
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rstorssp -8(%esi)
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/* Save the restore token on the old shadow stack. NB: This
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restore token may be checked by setcontext or swapcontext
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later. */
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saveprevssp
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/* Record the new shadow stack base that was switched to. */
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movl (oSSP + 4)(%eax), %ebx
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movl %ebx, %gs:SSP_BASE_OFFSET
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L(unwind_shadow_stack):
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rdsspd %ebx
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subl %edi, %ebx
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je L(skip_unwind_shadow_stack)
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negl %ebx
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shrl $2, %ebx
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movl $255, %esi
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L(loop):
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cmpl %esi, %ebx
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cmovb %ebx, %esi
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incsspd %esi
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subl %esi, %ebx
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ja L(loop)
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L(skip_unwind_shadow_stack):
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/* Load the values of all the preserved registers (except ESP). */
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movl oEDI(%eax), %edi
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movl oESI(%eax), %esi
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movl oEBP(%eax), %ebp
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movl oEBX(%eax), %ebx
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/* Get the return address set with getcontext. */
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movl oEIP(%eax), %ecx
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/* Check if return address is valid for the case when setcontext
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is invoked from L(exitcode) with linked context. */
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rdsspd %eax
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cmpl (%eax), %ecx
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/* Clear EAX to indicate success. NB: Don't use xorl to keep
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EFLAGS for jne. */
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movl $0, %eax
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jne L(jmp)
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/* Return to the new context if return address valid. */
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pushl %ecx
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ret
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L(jmp):
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/* Jump to the new context directly. */
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jmp *%ecx
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L(no_shstk):
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#endif
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/* Fetch the address to return to. */
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movl oEIP(%eax), %ecx
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/* Push the return address on the new stack so we can return there. */
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pushl %ecx
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/* Load the values of all the preserved registers (except ESP). */
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movl oEDI(%eax), %edi
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movl oESI(%eax), %esi
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movl oEBP(%eax), %ebp
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movl oEBX(%eax), %ebx
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/* All done, return 0 for success. */
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xorl %eax, %eax
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/* End FDE here, we fall into another context. */
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cfi_endproc
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cfi_startproc
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/* The following 'ret' will pop the address of the code and jump
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to it. */
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ret
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PSEUDO_END(__setcontext)
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libc_hidden_def (__setcontext)
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weak_alias (__setcontext, setcontext)
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