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-rw-r--r--sysdeps/unix/sysv/linux/i386/getcontext.S56
-rw-r--r--sysdeps/unix/sysv/linux/i386/makecontext.S123
-rw-r--r--sysdeps/unix/sysv/linux/i386/setcontext.S101
-rw-r--r--sysdeps/unix/sysv/linux/i386/swapcontext.S139
-rw-r--r--sysdeps/unix/sysv/linux/i386/sysdep.h5
-rw-r--r--sysdeps/unix/sysv/linux/i386/ucontext_i.sym4
6 files changed, 425 insertions, 3 deletions
diff --git a/sysdeps/unix/sysv/linux/i386/getcontext.S b/sysdeps/unix/sysv/linux/i386/getcontext.S
index 9c1df9a2aa..d91cfe4b1d 100644
--- a/sysdeps/unix/sysv/linux/i386/getcontext.S
+++ b/sysdeps/unix/sysv/linux/i386/getcontext.S
@@ -18,6 +18,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <sysdep.h>
+#include <asm/prctl.h>
 
 #include "ucontext_i.h"
 
@@ -42,6 +43,61 @@ ENTRY(__getcontext)
 	movw	%fs, %dx
 	movl	%edx, oFS(%eax)
 
+#if SHSTK_ENABLED
+	/* Check if shadow stack is enabled.  */
+	testl	$X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
+	jz	L(no_shstk)
+
+	/* Save EAX in EDX.  */
+	movl	%eax, %edx
+
+	xorl	%eax, %eax
+	cmpl	%gs:SSP_BASE_OFFSET, %eax
+	jnz	L(shadow_stack_bound_recorded)
+
+	/* Save EBX in the first scratch register slot.  */
+	movl	%ebx, oSCRATCH1(%edx)
+
+	/* Get the base address and size of the default shadow stack
+	   which must be the current shadow stack since nothing has
+	   been recorded yet.  */
+	sub	$24, %esp
+	mov	%esp, %ecx
+	movl	$ARCH_CET_STATUS, %ebx
+	movl	$__NR_arch_prctl, %eax
+	ENTER_KERNEL
+	testl	%eax, %eax
+	jz	L(continue_no_err)
+
+	/* This should never happen.  */
+	hlt
+
+L(continue_no_err):
+	/* Restore EBX from the first scratch register slot.  */
+	movl	oSCRATCH1(%edx), %ebx
+
+	/* Record the base of the current shadow stack.  */
+	movl	8(%esp), %eax
+	movl	%eax, %gs:SSP_BASE_OFFSET
+	add	$24, %esp
+
+L(shadow_stack_bound_recorded):
+	/* Load address of the context data structure.  */
+	movl	4(%esp), %eax
+
+	/* Get the current shadow stack pointer.  */
+	rdsspd	%edx
+	/* NB: Save the caller's shadow stack so that we can jump back
+	   to the caller directly.  */
+	addl	$4, %edx
+	movl	%edx, oSSP(%eax)
+
+	/* Save the current shadow stack base in ucontext.  */
+	movl	%gs:SSP_BASE_OFFSET, %edx
+	movl	%edx, (oSSP + 4)(%eax)
+
+L(no_shstk):
+#endif
 	/* We have separate floating-point register content memory on the
 	   stack.  We use the __fpregs_mem block in the context.  Set the
 	   links up correctly.  */
diff --git a/sysdeps/unix/sysv/linux/i386/makecontext.S b/sysdeps/unix/sysv/linux/i386/makecontext.S
index ad9ce5f977..91009675d1 100644
--- a/sysdeps/unix/sysv/linux/i386/makecontext.S
+++ b/sysdeps/unix/sysv/linux/i386/makecontext.S
@@ -18,6 +18,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <sysdep.h>
+#include <asm/prctl.h>
 
 #include "ucontext_i.h"
 
@@ -68,6 +69,127 @@ ENTRY(__makecontext)
 	jnz	1b
 2:
 
+#if SHSTK_ENABLED
+	/* Check if Shadow Stack is enabled.  */
+	testl	$X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
+	jz	L(skip_ssp)
+
+	/* Reload the pointer to ucontext.  */
+	movl	4(%esp), %eax
+
+	/* Shadow stack is enabled.  We need to allocate a new shadow
+	   stack.  */
+	subl	oSS_SP(%eax), %edx
+	shrl	$STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT, %edx
+
+	/* Align shadow stack size to 8 bytes.  */
+	addl	$7, %edx
+	andl	$-8, %edx
+
+	/* Store shadow stack size in __ssp[2].  */
+	movl	%edx, (oSSP + 8)(%eax)
+
+	/* Save ESI in the second scratch register slot.  */
+	movl	%esi, oSCRATCH2(%eax)
+	/* Save EDI in the third scratch register slot.  */
+	movl	%edi, oSCRATCH3(%eax)
+
+	/* Save the pointer to ucontext.  */
+	movl	%eax, %edi
+
+	/* Get the original shadow stack pointer.  */
+	rdsspd	%esi
+
+	/* Align the saved original shadow stack pointer to the next
+	   8 byte aligned boundary.  */
+	andl	$-8, %esi
+
+	/* Load the top of the new stack into EDX.  */
+	movl	oESP(%eax), %edx
+
+	/* We need to terminate the FDE here because the unwinder looks
+	   at ra-1 for unwind information.  */
+	cfi_endproc
+
+	/* Swap the original stack pointer with the top of the new
+	   stack.  */
+	xchgl	%esp, %edx
+
+	/* Add 4 bytes since CALL will push the 4-byte return address
+	   onto stack.  */
+	addl	$4, %esp
+
+	/* Allocate the new shadow stack.  Save EBX in the first scratch
+	   register slot.  */
+	movl	%ebx, oSCRATCH1(%eax)
+
+	/* CET syscall takes 64-bit sizes.  */
+	subl	$16, %esp
+	movl	(oSSP + 8)(%eax), %ecx
+	movl	%ecx, (%esp)
+	movl	$0, 4(%esp)
+	movl	%ecx, 8(%esp)
+	movl	$0, 12(%esp)
+	movl	%esp, %ecx
+
+	movl	$ARCH_CET_ALLOC_SHSTK, %ebx
+	movl	$__NR_arch_prctl, %eax
+	ENTER_KERNEL
+	testl	%eax, %eax
+	jne	L(hlt)		/* This should never happen.  */
+
+	/* Copy the base address of the new shadow stack to __ssp[1].  */
+	movl	(%esp), %eax
+	movl	%eax, (oSSP + 4)(%edi)
+
+	addl	$16, %esp
+
+	/* Restore EBX from the first scratch register slot.  */
+	movl	oSCRATCH1(%edi), %ebx
+
+	/* Get the size of the new shadow stack.  */
+	movl	(oSSP + 8)(%edi), %ecx
+
+	/* Use the restore stoken to restore the new shadow stack.  */
+	rstorssp -8(%eax, %ecx)
+
+	/* Save the restore token at the next 8 byte aligned boundary
+	   on the original shadow stack.  */
+	saveprevssp
+
+	/* Push the address of "jmp exitcode" onto the new stack as
+	   well as the new shadow stack.  */
+	call	1f
+	jmp	L(exitcode)
+1:
+
+	/* Get the new shadow stack pointer.  */
+	rdsspd	%eax
+
+	/* Use the restore stoken to restore the original shadow stack.  */
+	rstorssp -8(%esi)
+
+	/* Save the restore token on the new shadow stack.  */
+	saveprevssp
+
+	/* Store the new shadow stack pointer in __ssp[0].  */
+	movl	%eax, oSSP(%edi)
+
+	/* Restore the original stack.  */
+	mov	%edx, %esp
+
+	cfi_startproc
+
+	/* Restore ESI from the second scratch register slot.  */
+	movl	oSCRATCH2(%edi), %esi
+	/* Restore EDI from the third scratch register slot.  */
+	movl	oSCRATCH3(%edi), %edi
+
+	ret
+
+L(skip_ssp):
+#endif
+
 	/* If the function we call returns we must continue with the
 	   context which is given in the uc_link element.  To do this
 	   set the return address for the function the user provides
@@ -123,6 +245,7 @@ L(call_exit):
 	call	HIDDEN_JUMPTARGET(exit)
 	/* The 'exit' call should never return.  In case it does cause
 	   the process to terminate.  */
+L(hlt):
 	hlt
 	cfi_startproc
 END(__makecontext)
diff --git a/sysdeps/unix/sysv/linux/i386/setcontext.S b/sysdeps/unix/sysv/linux/i386/setcontext.S
index f042d80bf4..332b5147bc 100644
--- a/sysdeps/unix/sysv/linux/i386/setcontext.S
+++ b/sysdeps/unix/sysv/linux/i386/setcontext.S
@@ -18,6 +18,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <sysdep.h>
+#include <asm/prctl.h>
 
 #include "ucontext_i.h"
 
@@ -56,9 +57,6 @@ ENTRY(__setcontext)
 	movl	oFS(%eax), %ecx
 	movw	%cx, %fs
 
-	/* Fetch the address to return to.  */
-	movl	oEIP(%eax), %ecx
-
 	/* Load the new stack pointer.  */
 	cfi_def_cfa (eax, 0)
 	cfi_offset (edi, oEDI)
@@ -67,6 +65,103 @@ ENTRY(__setcontext)
 	cfi_offset (ebx, oEBX)
 	movl	oESP(%eax), %esp
 
+#if SHSTK_ENABLED
+	/* Check if Shadow Stack is enabled.  */
+	testl	$X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
+	jz	L(no_shstk)
+
+	/* If the base of the target shadow stack is the same as the
+	   base of the current shadow stack, we unwind the shadow
+	   stack.  Otherwise it is a stack switch and we look for a
+	   restore token.  */
+	movl	oSSP(%eax), %esi
+	movl	%esi, %edi
+
+	/* Get the base of the target shadow stack.  */
+	movl	(oSSP + 4)(%eax), %ecx
+	cmpl	%gs:SSP_BASE_OFFSET, %ecx
+	je	L(unwind_shadow_stack)
+
+	/* Align the saved original shadow stack pointer to the next
+	   8 byte aligned boundary.  */
+	andl	$-8, %esi
+
+L(find_restore_token_loop):
+	/* Look for a restore token.  */
+	movl	-8(%esi), %ebx
+	andl	$-8, %ebx
+	cmpl	%esi, %ebx
+	je	L(restore_shadow_stack)
+
+	/* Try the next slot.  */
+	subl	$8, %esi
+	jmp	L(find_restore_token_loop)
+
+L(restore_shadow_stack):
+	/* Pop return address from the shadow stack since setcontext
+	   will not return.  */
+	movl	$1, %ebx
+	incsspd	%ebx
+
+	/* Use the restore stoken to restore the target shadow stack.  */
+	rstorssp -8(%esi)
+
+	/* Save the restore token on the old shadow stack.  NB: This
+	   restore token may be checked by setcontext or swapcontext
+	   later.  */
+	saveprevssp
+
+	/* Record the new shadow stack base that was switched to.  */
+	movl	(oSSP + 4)(%eax), %ebx
+	movl	%ebx, %gs:SSP_BASE_OFFSET
+
+L(unwind_shadow_stack):
+	rdsspd	%ebx
+	subl	%edi, %ebx
+	je	L(skip_unwind_shadow_stack)
+	negl	%ebx
+	shrl	$2, %ebx
+	movl	$255, %esi
+L(loop):
+	cmpl	%esi, %ebx
+	cmovb	%ebx, %esi
+	incsspd	%esi
+	subl	%esi, %ebx
+	ja	L(loop)
+
+L(skip_unwind_shadow_stack):
+
+	/* Load the values of all the preserved registers (except ESP).  */
+	movl	oEDI(%eax), %edi
+	movl	oESI(%eax), %esi
+	movl	oEBP(%eax), %ebp
+	movl	oEBX(%eax), %ebx
+
+	/* Get the return address set with getcontext.  */
+	movl	oEIP(%eax), %ecx
+
+	/* Check if return address is valid for the case when setcontext
+	   is invoked from L(exitcode) with linked context.  */
+	rdsspd	%eax
+	cmpl	(%eax), %ecx
+	/* Clear EAX to indicate success.  NB: Don't use xorl to keep
+	   EFLAGS for jne.  */
+	movl	$0, %eax
+	jne	L(jmp)
+	/* Return to the new context if return address valid.  */
+	pushl	%ecx
+	ret
+
+L(jmp):
+	/* Jump to the new context directly.  */
+	jmp	*%ecx
+
+L(no_shstk):
+#endif
+
+	/* Fetch the address to return to.  */
+	movl	oEIP(%eax), %ecx
+
 	/* Push the return address on the new stack so we can return there.  */
 	pushl	%ecx
 
diff --git a/sysdeps/unix/sysv/linux/i386/swapcontext.S b/sysdeps/unix/sysv/linux/i386/swapcontext.S
index 090c2d8c3e..203eafa2e7 100644
--- a/sysdeps/unix/sysv/linux/i386/swapcontext.S
+++ b/sysdeps/unix/sysv/linux/i386/swapcontext.S
@@ -18,6 +18,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <sysdep.h>
+#include <asm/prctl.h>
 
 #include "ucontext_i.h"
 
@@ -76,6 +77,144 @@ ENTRY(__swapcontext)
 	movl	oFS(%eax), %edx
 	movw	%dx, %fs
 
+#if SHSTK_ENABLED
+	/* Check if Shadow Stack is enabled.  */
+	testl	$X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
+	jz	L(no_shstk)
+
+	xorl	%eax, %eax
+	cmpl	%gs:SSP_BASE_OFFSET, %eax
+	jnz	L(shadow_stack_bound_recorded)
+
+	/* Get the base address and size of the default shadow stack
+	   which must be the current shadow stack since nothing has
+	   been recorded yet.  */
+	sub	$24, %esp
+	mov	%esp, %ecx
+	movl	$ARCH_CET_STATUS, %ebx
+	movl	$__NR_arch_prctl, %eax
+	ENTER_KERNEL
+	testl	%eax, %eax
+	jz	L(continue_no_err)
+
+	/* This should never happen.  */
+	hlt
+
+L(continue_no_err):
+	/* Record the base of the current shadow stack.  */
+	movl	8(%esp), %eax
+	movl	%eax, %gs:SSP_BASE_OFFSET
+	add	$24, %esp
+
+L(shadow_stack_bound_recorded):
+	/* Load address of the context data structure we save in.  */
+	movl	4(%esp), %eax
+
+	/* Load address of the context data structure we swap in  */
+	movl	8(%esp), %edx
+
+       /* If we unwind the stack, we can't undo stack unwinding.  Just
+	   save the target shadow stack pointer as the current shadow
+	   stack pointer.   */
+	movl	oSSP(%edx), %ecx
+	movl	%ecx, oSSP(%eax)
+
+	/* Save the current shadow stack base in ucontext.  */
+	movl	%gs:SSP_BASE_OFFSET, %ecx
+	movl	%ecx, (oSSP + 4)(%eax)
+
+	/* If the base of the target shadow stack is the same as the
+	   base of the current shadow stack, we unwind the shadow
+	   stack.  Otherwise it is a stack switch and we look for a
+	   restore token.  */
+	movl	oSSP(%edx), %esi
+	movl	%esi, %edi
+
+	/* Get the base of the target shadow stack.  */
+	movl	(oSSP + 4)(%edx), %ecx
+	cmpl	%gs:SSP_BASE_OFFSET, %ecx
+	je	L(unwind_shadow_stack)
+
+	/* Align the saved original shadow stack pointer to the next
+	   8 byte aligned boundary.  */
+	andl	$-8, %esi
+
+L(find_restore_token_loop):
+	/* Look for a restore token.  */
+	movl	-8(%esi), %ebx
+	andl	$-8, %ebx
+	cmpl	%esi, %ebx
+	je	L(restore_shadow_stack)
+
+	/* Try the next slot.  */
+	subl	$8, %esi
+	jmp	L(find_restore_token_loop)
+
+L(restore_shadow_stack):
+	/* The target shadow stack will be restored.  Save the current
+	   shadow stack pointer.  */
+	rdsspd	%ecx
+	movl	%ecx, oSSP(%eax)
+
+	/* Use the restore stoken to restore the target shadow stack.  */
+	rstorssp -8(%esi)
+
+	/* Save the restore token on the old shadow stack.  NB: This
+	   restore token may be checked by setcontext or swapcontext
+	   later.  */
+	saveprevssp
+
+	/* Record the new shadow stack base that was switched to.  */
+	movl	(oSSP + 4)(%edx), %ebx
+	movl	%ebx, %gs:SSP_BASE_OFFSET
+
+L(unwind_shadow_stack):
+	rdsspd	%ebx
+	subl	%edi, %ebx
+	je	L(skip_unwind_shadow_stack)
+	negl	%ebx
+	shrl	$2, %ebx
+	movl	$255, %esi
+L(loop):
+	cmpl	%esi, %ebx
+	cmovb	%ebx, %esi
+	incsspd	%esi
+	subl	%esi, %ebx
+	ja	L(loop)
+
+L(skip_unwind_shadow_stack):
+
+	/* Load the new stack pointer.  */
+	movl	oESP(%edx), %esp
+
+	/* Load the values of all the preserved registers (except ESP).  */
+	movl	oEDI(%edx), %edi
+	movl	oESI(%edx), %esi
+	movl	oEBP(%edx), %ebp
+	movl	oEBX(%edx), %ebx
+
+	/* Get the return address set with getcontext.  */
+	movl	oEIP(%edx), %ecx
+
+	/* Check if return address is valid for the case when setcontext
+	   is invoked from L(exitcode) with linked context.  */
+	rdsspd	%eax
+	cmpl	(%eax), %ecx
+	/* Clear EAX to indicate success.  NB: Don't use xorl to keep
+	   EFLAGS for jne.  */
+	movl	$0, %eax
+	jne	L(jmp)
+	/* Return to the new context if return address valid.  */
+	pushl	%ecx
+	ret
+
+L(jmp):
+	/* Jump to the new context directly.  */
+	jmp	*%ecx
+
+L(no_shstk):
+#endif
+
 	/* Fetch the address to return to.  */
 	movl	oEIP(%eax), %ecx
 
diff --git a/sysdeps/unix/sysv/linux/i386/sysdep.h b/sysdeps/unix/sysv/linux/i386/sysdep.h
index 4aa7bb496a..420b6a7912 100644
--- a/sysdeps/unix/sysv/linux/i386/sysdep.h
+++ b/sysdeps/unix/sysv/linux/i386/sysdep.h
@@ -662,4 +662,9 @@ struct libc_do_syscall_args
 # endif
 #endif
 
+/* Each shadow stack slot takes 4 bytes.  Assuming that each stack
+   frame takes 128 bytes, this is used to compute shadow stack size
+   from stack size.  */
+#define STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT 5
+
 #endif /* linux/i386/sysdep.h */
diff --git a/sysdeps/unix/sysv/linux/i386/ucontext_i.sym b/sysdeps/unix/sysv/linux/i386/ucontext_i.sym
index 1dfe03d2cc..1d8608eafc 100644
--- a/sysdeps/unix/sysv/linux/i386/ucontext_i.sym
+++ b/sysdeps/unix/sysv/linux/i386/ucontext_i.sym
@@ -22,6 +22,10 @@ oEBP		mreg (EBP)
 oESP		mreg (ESP)
 oEBX		mreg (EBX)
 oEIP		mreg (EIP)
+oSCRATCH1	mreg (EAX)
+oSCRATCH2	mreg (ECX)
+oSCRATCH3	mreg (EDX)
 oFPREGS		mcontext (fpregs)
 oSIGMASK	ucontext (uc_sigmask)
 oFPREGSMEM	ucontext (__fpregs_mem)
+oSSP		ucontext (__ssp)
generated by cgit-pink 1.4.1 (git 2.36.1) at 2024-07-15 08:49:31 +0000