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x86: Update vfork to pop shadow stack
The shadow stack prevents us from pushing the saved return PC onto the stack and returning normally. Instead we pop the shadow stack and return directly. This is the safest way to return and ensures any stack manipulations done by the vfork'd child doesn't cause the parent to terminate when CET is enabled. Reviewed-by: Carlos O'Donell <carlos@redhat.com> * sysdeps/unix/sysv/linux/i386/vfork.S (SYSCALL_ERROR_HANDLER): Redefine if shadow stack is enabled. (SYSCALL_ERROR_LABEL): Likewise. (__vfork): Pop shadow stack and jump back to to caller directly when shadow stack is in use. * sysdeps/unix/sysv/linux/x86_64/vfork.S (SYSCALL_ERROR_HANDLER): Redefine if shadow stack is enabled. (SYSCALL_ERROR_LABEL): Likewise. (__vfork): Pop shadow stack and jump back to to caller directly when shadow stack is in use.
This commit is contained in:
H.J. Lu
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ca027e0f62
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ChangeLog
13
ChangeLog
@ -1,3 +1,16 @@
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2018-07-24 H.J. Lu <hongjiu.lu@intel.com>
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* sysdeps/unix/sysv/linux/i386/vfork.S (SYSCALL_ERROR_HANDLER):
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Redefine if shadow stack is enabled.
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(SYSCALL_ERROR_LABEL): Likewise.
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(__vfork): Pop shadow stack and jump back to to caller directly
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when shadow stack is in use.
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* sysdeps/unix/sysv/linux/x86_64/vfork.S (SYSCALL_ERROR_HANDLER):
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Redefine if shadow stack is enabled.
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(SYSCALL_ERROR_LABEL): Likewise.
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(__vfork): Pop shadow stack and jump back to to caller directly
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when shadow stack is in use.
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2018-07-24 H.J. Lu <hongjiu.lu@intel.com>
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* sysdeps/x86_64/tst-quadmod1.S (func): Add endbr64 if IBT is
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@ -21,6 +21,38 @@
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#include <bits/errno.h>
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#include <tcb-offsets.h>
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#if SHSTK_ENABLED
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/* The shadow stack prevents us from pushing the saved return PC onto
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the stack and returning normally. Instead we pop the shadow stack
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and return directly. This is the safest way to return and ensures
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any stack manipulations done by the vfork'd child doesn't cause the
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parent to terminate when CET is enabled. */
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# undef SYSCALL_ERROR_HANDLER
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# ifdef PIC
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# define SYSCALL_ERROR_HANDLER \
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0: \
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calll .L1; \
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.L1: \
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popl %edx; \
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.L2: \
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addl $_GLOBAL_OFFSET_TABLE_ + (.L2 - .L1), %edx; \
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movl __libc_errno@gotntpoff(%edx), %edx; \
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negl %eax; \
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movl %eax, %gs:(%edx); \
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orl $-1, %eax; \
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jmp 1b;
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# else
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# define SYSCALL_ERROR_HANDLER \
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0: \
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movl __libc_errno@indntpoff, %edx; \
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negl %eax; \
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movl %eax, %gs:(%edx); \
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orl $-1, %eax; \
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jmp 1b;
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# endif
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# undef SYSCALL_ERROR_LABEL
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# define SYSCALL_ERROR_LABEL 0f
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#endif
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/* Clone the calling process, but without copying the whole address space.
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The calling process is suspended until the new process exits or is
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@ -38,16 +70,41 @@ ENTRY (__vfork)
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movl $SYS_ify (vfork), %eax
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int $0x80
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#if !SHSTK_ENABLED
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/* Jump to the return PC. Don't jump directly since this
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disturbs the branch target cache. Instead push the return
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address back on the stack. */
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pushl %ecx
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cfi_adjust_cfa_offset (4)
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#endif
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cmpl $-4095, %eax
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/* Branch forward if it failed. */
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jae SYSCALL_ERROR_LABEL
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#if SHSTK_ENABLED
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1:
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/* Check if shadow stack is in use. */
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xorl %edx, %edx
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rdsspd %edx
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testl %edx, %edx
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/* Normal return if shadow stack isn't in use. */
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je L(no_shstk)
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/* Pop return address from shadow stack and jump back to caller
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directly. */
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movl $1, %edx
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incsspd %edx
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jmp *%ecx
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L(no_shstk):
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/* Jump to the return PC. Don't jump directly since this
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disturbs the branch target cache. Instead push the return
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address back on the stack. */
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pushl %ecx
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cfi_adjust_cfa_offset (4)
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#endif
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ret
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PSEUDO_END (__vfork)
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@ -20,6 +20,21 @@
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#include <bits/errno.h>
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#include <tcb-offsets.h>
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#if SHSTK_ENABLED
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/* The shadow stack prevents us from pushing the saved return PC onto
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the stack and returning normally. Instead we pop the shadow stack
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and return directly. This is the safest way to return and ensures
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any stack manipulations done by the vfork'd child doesn't cause the
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parent to terminate when CET is enabled. */
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# undef SYSCALL_ERROR_HANDLER
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# define SYSCALL_ERROR_HANDLER \
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0: \
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SYSCALL_SET_ERRNO; \
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or $-1, %RAX_LP; \
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jmp 1b;
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# undef SYSCALL_ERROR_LABEL
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# define SYSCALL_ERROR_LABEL 0f
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#endif
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/* Clone the calling process, but without copying the whole address space.
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The calling process is suspended until the new process exits or is
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@ -38,13 +53,36 @@ ENTRY (__vfork)
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movl $SYS_ify (vfork), %eax
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syscall
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#if !SHSTK_ENABLED
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/* Push back the return PC. */
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pushq %rdi
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cfi_adjust_cfa_offset(8)
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#endif
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cmpl $-4095, %eax
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jae SYSCALL_ERROR_LABEL /* Branch forward if it failed. */
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#if SHSTK_ENABLED
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1:
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/* Check if shadow stack is in use. */
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xorl %esi, %esi
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rdsspq %rsi
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testq %rsi, %rsi
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/* Normal return if shadow stack isn't in use. */
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je L(no_shstk)
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/* Pop return address from shadow stack and jump back to caller
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directly. */
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movl $1, %esi
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incsspq %rsi
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jmp *%rdi
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L(no_shstk):
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/* Push back the return PC. */
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pushq %rdi
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cfi_adjust_cfa_offset(8)
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#endif
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/* Normal return. */
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ret
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