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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>
134 lines
3.7 KiB
ArmAsm
134 lines
3.7 KiB
ArmAsm
/* Save current 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(__getcontext)
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/* Load address of the context data structure. */
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movl 4(%esp), %eax
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/* Save the preserved register values and the return address. */
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movl %edi, oEDI(%eax)
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movl %esi, oESI(%eax)
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movl %ebp, oEBP(%eax)
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movl (%esp), %ecx
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movl %ecx, oEIP(%eax)
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leal 4(%esp), %ecx /* Exclude the return address. */
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movl %ecx, oESP(%eax)
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movl %ebx, oEBX(%eax)
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/* Save 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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xorl %edx, %edx
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movw %fs, %dx
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movl %edx, oFS(%eax)
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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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/* Save EAX in EDX. */
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movl %eax, %edx
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xorl %eax, %eax
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cmpl %gs:SSP_BASE_OFFSET, %eax
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jnz L(shadow_stack_bound_recorded)
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/* Save EBX in the first scratch register slot. */
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movl %ebx, oSCRATCH1(%edx)
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/* Get the base address and size of the default shadow stack
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which must be the current shadow stack since nothing has
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been recorded yet. */
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sub $24, %esp
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mov %esp, %ecx
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movl $ARCH_CET_STATUS, %ebx
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movl $__NR_arch_prctl, %eax
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ENTER_KERNEL
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testl %eax, %eax
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jz L(continue_no_err)
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/* This should never happen. */
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hlt
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L(continue_no_err):
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/* Restore EBX from the first scratch register slot. */
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movl oSCRATCH1(%edx), %ebx
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/* Record the base of the current shadow stack. */
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movl 8(%esp), %eax
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movl %eax, %gs:SSP_BASE_OFFSET
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add $24, %esp
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L(shadow_stack_bound_recorded):
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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 shadow stack pointer. */
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rdsspd %edx
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/* NB: Save the caller's shadow stack so that we can jump back
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to the caller directly. */
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addl $4, %edx
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movl %edx, oSSP(%eax)
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/* Save the current shadow stack base in ucontext. */
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movl %gs:SSP_BASE_OFFSET, %edx
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movl %edx, (oSSP + 4)(%eax)
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L(no_shstk):
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#endif
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/* We have separate floating-point register content memory on the
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stack. We use the __fpregs_mem block in the context. Set the
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links up correctly. */
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leal oFPREGSMEM(%eax), %ecx
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movl %ecx, oFPREGS(%eax)
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/* Save the floating-point context. */
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fnstenv (%ecx)
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/* And load it right back since the processor changes the mask.
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Intel thought this opcode to be used in interrupt handlers which
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would block all exceptions. */
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fldenv (%ecx)
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/* Save the current signal mask. */
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pushl %ebx
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cfi_adjust_cfa_offset (4)
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cfi_rel_offset (ebx, 0)
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leal oSIGMASK(%eax), %edx
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xorl %ecx, %ecx
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movl $SIG_BLOCK, %ebx
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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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/* All done, return 0 for success. */
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xorl %eax, %eax
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ret
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PSEUDO_END(__getcontext)
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weak_alias (__getcontext, getcontext)
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