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, 44 insertions, 0 deletions

diff --git a/sysdeps/x86_64/__longjmp.S b/sysdeps/x86_64/__longjmp.S
index a487e0efd0..d7d123e4bc 100644
--- a/sysdeps/x86_64/__longjmp.S
+++ b/sysdeps/x86_64/__longjmp.S
@@ -17,9 +17,18 @@
 
 #include <sysdep.h>
 #include <jmpbuf-offsets.h>
+#include <jmp_buf-ssp.h>
 #include <asm-syntax.h>
 #include <stap-probe.h>
 
+/* Don't restore shadow stack register if
+   1. Shadow stack isn't enabled.  Or
+   2. __longjmp is defined for __longjmp_cancel.
+ */
+#if !SHSTK_ENABLED || defined __longjmp
+# undef SHADOW_STACK_POINTER_OFFSET
+#endif
+
 /* Jump to the position specified by ENV, causing the
    setjmp call there to return VAL, or 1 if VAL is 0.
    void __longjmp (__jmp_buf env, int val).  */
@@ -42,6 +51,41 @@ ENTRY(__longjmp)
 	orq %rax, %r9
 # endif
 #endif
+#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.  */
+	/* Get the current ssp.  */
+	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)