x86: Support shadow stack pointer in setjmp/longjmp

Save and restore shadow stack pointer in setjmp and longjmp to support
shadow stack in Intel CET.  Use feature_1 in tcbhead_t to check if
shadow stack is enabled before saving and restoring shadow stack pointer.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

	* sysdeps/i386/__longjmp.S: Include <jmp_buf-ssp.h>.
	(__longjmp): Restore shadow stack pointer if shadow stack is
	enabled, SHADOW_STACK_POINTER_OFFSET is defined and __longjmp
	isn't defined for __longjmp_cancel.
	* sysdeps/i386/bsd-_setjmp.S: Include <jmp_buf-ssp.h>.
	(_setjmp): Save shadow stack pointer if shadow stack is enabled
	and SHADOW_STACK_POINTER_OFFSET is defined.
	* sysdeps/i386/bsd-setjmp.S: Include <jmp_buf-ssp.h>.
	(setjmp): Save shadow stack pointer if shadow stack is enabled
	and SHADOW_STACK_POINTER_OFFSET is defined.
	* sysdeps/i386/setjmp.S: Include <jmp_buf-ssp.h>.
	(__sigsetjmp): Save shadow stack pointer if shadow stack is
	enabled and SHADOW_STACK_POINTER_OFFSET is defined.
	* sysdeps/unix/sysv/linux/i386/____longjmp_chk.S: Include
	<jmp_buf-ssp.h>.
	(____longjmp_chk): Restore shadow stack pointer if shadow stack
	is enabled and SHADOW_STACK_POINTER_OFFSET is defined.
	* sysdeps/unix/sysv/linux/x86/Makefile (gen-as-const-headers):
	Remove jmp_buf-ssp.sym.
	* sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S: Include
	<jmp_buf-ssp.h>.
	(____longjmp_chk): Restore shadow stack pointer if shadow stack
	is enabled and SHADOW_STACK_POINTER_OFFSET is defined.
	* sysdeps/x86/Makefile (gen-as-const-headers): Add
	jmp_buf-ssp.sym.
	* sysdeps/x86/jmp_buf-ssp.sym: New dummy file.
	* sysdeps/x86_64/__longjmp.S: Include <jmp_buf-ssp.h>.
	(__longjmp): Restore shadow stack pointer if shadow stack is
	enabled, SHADOW_STACK_POINTER_OFFSET is defined and __longjmp
	isn't defined for __longjmp_cancel.
	* sysdeps/x86_64/setjmp.S: Include <jmp_buf-ssp.h>.
	(__sigsetjmp): Save shadow stack pointer if shadow stack is
	enabled and SHADOW_STACK_POINTER_OFFSET is defined.

1 files changed, 38 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S b/sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S
index 8a9f2e1a3c..7eb26fafca 100644
--- a/sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S
+++ b/sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S
@@ -20,7 +20,13 @@
 #include <asm-syntax.h>
 #include <stap-probe.h>
 
+/* Don't restore shadow stack register if shadow stack isn't enabled.  */
+#if !SHSTK_ENABLED
+# undef SHADOW_STACK_POINTER_OFFSET
+#endif
+
 #include <sigaltstack-offsets.h>
+#include <jmp_buf-ssp.h>
 
 	.section .rodata.str1.1,"aMS",@progbits,1
 	.type	longjmp_msg,@object
@@ -105,6 +111,38 @@ ENTRY(____longjmp_chk)
 	cfi_restore (%rsi)
 
 .Lok:
+#ifdef SHADOW_STACK_POINTER_OFFSET
+# if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
+	/* Check if Shadow Stack is enabled.  */
+	testl	$X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
+	jz	L(skip_ssp)
+# else
+	xorl	%eax, %eax
+# endif
+	/* Check and adjust the Shadow-Stack-Pointer.  */
+	rdsspq	%rax
+	/* And compare it with the saved ssp value.  */
+	subq	SHADOW_STACK_POINTER_OFFSET(%rdi), %rax
+	je	L(skip_ssp)
+	/* Count the number of frames to adjust and adjust it
+	   with incssp instruction.  The instruction can adjust
+	   the ssp by [0..255] value only thus use a loop if
+	   the number of frames is bigger than 255.  */
+	negq	%rax
+	shrq	$3, %rax
+	/* NB: We saved Shadow-Stack-Pointer of setjmp.  Since we are
+	       restoring Shadow-Stack-Pointer of setjmp's caller, we
+	       need to unwind shadow stack by one more frame.  */
+	addq	$1, %rax
+	movl	$255, %ebx
+L(loop):
+	cmpq	%rbx, %rax
+	cmovb	%rax, %rbx
+	incsspq	%rbx
+	subq	%rbx, %rax
+	ja	L(loop)
+L(skip_ssp):
+#endif
 	LIBC_PROBE (longjmp, 3, LP_SIZE@%RDI_LP, -4@%esi, LP_SIZE@%RDX_LP)
 	/* We add unwind information for the target here.  */
 	cfi_def_cfa(%rdi, 0)