x86/ibt,xen: Sprinkle the ENDBR

Even though Xen currently doesn't advertise IBT, prepare for when it
will eventually do so and sprinkle the ENDBR dust accordingly.

Even though most of the entry points are IRET like, the CPL0
Hypervisor can set WAIT-FOR-ENDBR and demand ENDBR at these sites.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.873919996@infradead.org

arch/x86/entry/entry_64.S

@@ -809,6 +809,7 @@ SYM_CODE_END(exc_xen_hypervisor_callback)
  */
 SYM_CODE_START(xen_failsafe_callback)
 	UNWIND_HINT_EMPTY
+	ENDBR
 	movl	%ds, %ecx
 	cmpw	%cx, 0x10(%rsp)
 	jne	1f

arch/x86/include/asm/segment.h

@@ -283,7 +283,7 @@ static inline void vdso_read_cpunode(unsigned *cpu, unsigned *node)
  * pop %rcx; pop %r11; jmp early_idt_handler_array[i]; summing up to
  * max 8 bytes.
  */
-#define XEN_EARLY_IDT_HANDLER_SIZE 8
+#define XEN_EARLY_IDT_HANDLER_SIZE (8 + ENDBR_INSN_SIZE)
 
 #ifndef __ASSEMBLY__
 

arch/x86/kernel/head_64.S

@@ -383,6 +383,7 @@ SYM_CODE_START(early_idt_handler_array)
 	.endr
 	UNWIND_HINT_IRET_REGS offset=16
 SYM_CODE_END(early_idt_handler_array)
+	ANNOTATE_NOENDBR // early_idt_handler_array[NUM_EXCEPTION_VECTORS]
 
 SYM_CODE_START_LOCAL(early_idt_handler_common)
 	/*

arch/x86/xen/enlighten_pv.c

@@ -624,6 +624,9 @@ static struct trap_array_entry trap_array[] = {
 	TRAP_ENTRY(exc_coprocessor_error,		false ),
 	TRAP_ENTRY(exc_alignment_check,			false ),
 	TRAP_ENTRY(exc_simd_coprocessor_error,		false ),
+#ifdef CONFIG_X86_KERNEL_IBT
+	TRAP_ENTRY(exc_control_protection,		false ),
+#endif
 };
 
 static bool __ref get_trap_addr(void **addr, unsigned int ist)

arch/x86/xen/xen-asm.S

@@ -122,6 +122,7 @@ SYM_FUNC_END(xen_read_cr2_direct);
 .macro xen_pv_trap name
 SYM_CODE_START(xen_\name)
 	UNWIND_HINT_EMPTY
+	ENDBR
 	pop %rcx
 	pop %r11
 	jmp  \name
@@ -147,6 +148,9 @@ xen_pv_trap asm_exc_page_fault
 xen_pv_trap asm_exc_spurious_interrupt_bug
 xen_pv_trap asm_exc_coprocessor_error
 xen_pv_trap asm_exc_alignment_check
+#ifdef CONFIG_X86_KERNEL_IBT
+xen_pv_trap asm_exc_control_protection
+#endif
 #ifdef CONFIG_X86_MCE
 xen_pv_trap asm_xenpv_exc_machine_check
 #endif /* CONFIG_X86_MCE */
@@ -162,6 +166,7 @@ SYM_CODE_START(xen_early_idt_handler_array)
 	i = 0
 	.rept NUM_EXCEPTION_VECTORS
 	UNWIND_HINT_EMPTY
+	ENDBR
 	pop %rcx
 	pop %r11
 	jmp early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE
@@ -231,6 +236,7 @@ SYM_CODE_END(xenpv_restore_regs_and_return_to_usermode)
 /* Normal 64-bit system call target */
 SYM_CODE_START(xen_syscall_target)
 	UNWIND_HINT_EMPTY
+	ENDBR
 	popq %rcx
 	popq %r11
 
@@ -250,6 +256,7 @@ SYM_CODE_END(xen_syscall_target)
 /* 32-bit compat syscall target */
 SYM_CODE_START(xen_syscall32_target)
 	UNWIND_HINT_EMPTY
+	ENDBR
 	popq %rcx
 	popq %r11
 
@@ -267,6 +274,7 @@ SYM_CODE_END(xen_syscall32_target)
 /* 32-bit compat sysenter target */
 SYM_CODE_START(xen_sysenter_target)
 	UNWIND_HINT_EMPTY
+	ENDBR
 	/*
 	 * NB: Xen is polite and clears TF from EFLAGS for us.  This means
 	 * that we don't need to guard against single step exceptions here.
@@ -290,6 +298,7 @@ SYM_CODE_END(xen_sysenter_target)
 SYM_CODE_START(xen_syscall32_target)
 SYM_CODE_START(xen_sysenter_target)
 	UNWIND_HINT_EMPTY
+	ENDBR
 	lea 16(%rsp), %rsp	/* strip %rcx, %r11 */
 	mov $-ENOSYS, %rax
 	pushq $0

arch/x86/xen/xen-head.S

@@ -25,8 +25,12 @@
 SYM_CODE_START(hypercall_page)
 	.rept (PAGE_SIZE / 32)
 		UNWIND_HINT_FUNC
-		.skip 31, 0x90
-		RET
+		ANNOTATE_NOENDBR
+		ret
+		/*
+		 * Xen will write the hypercall page, and sort out ENDBR.
+		 */
+		.skip 31, 0xcc
 	.endr
 
 #define HYPERCALL(n) \
@@ -74,6 +78,7 @@ SYM_CODE_END(startup_xen)
 .pushsection .text
 SYM_CODE_START(asm_cpu_bringup_and_idle)
 	UNWIND_HINT_EMPTY
+	ENDBR
 
 	call cpu_bringup_and_idle
 SYM_CODE_END(asm_cpu_bringup_and_idle)