[PATCH v2 67/70] x86/entry: Make IDT entrypoints CET-IBT compatible

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Each IDT vector needs to land on an endbr64 instruction.  This is especially
important for the #CP handler, which will recurse indefinitely if the endbr64
is missing, eventually escalating to #DF if guard pages are active.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>

v2:
 * Extra newlines in asm
 * Reword commit message
---
 xen/arch/x86/x86_64/compat/entry.S |  1 +
 xen/arch/x86/x86_64/entry.S        | 30 ++++++++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/x86_64/compat/entry.S 
b/xen/arch/x86/x86_64/compat/entry.S
index c84ff7ea6476..5fd6dbbd4513 100644
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -12,6 +12,7 @@
 #include <irq_vectors.h>
 
 ENTRY(entry_int82)
+        ENDBR64
         ALTERNATIVE "", clac, X86_FEATURE_XEN_SMAP
         pushq $0
         movl  $HYPERCALL_VECTOR, 4(%rsp)
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index 9abcf95bd010..ea6f0afbc2b4 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -386,6 +386,7 @@ UNLIKELY_END(sysenter_gpf)
         jmp   .Lbounce_exception
 
 ENTRY(int80_direct_trap)
+        ENDBR64
         ALTERNATIVE "", clac, X86_FEATURE_XEN_SMAP
         pushq $0
         movl  $0x80, 4(%rsp)
@@ -698,6 +699,7 @@ ENTRY(common_interrupt)
         jmp ret_from_intr
 
 ENTRY(page_fault)
+        ENDBR64
         movl  $TRAP_page_fault,4(%rsp)
 /* No special register assumptions. */
 GLOBAL(handle_exception)
@@ -872,75 +874,91 @@ FATAL_exception_with_ints_disabled:
         BUG   /* fatal_trap() shouldn't return. */
 
 ENTRY(divide_error)
+        ENDBR64
         pushq $0
         movl  $TRAP_divide_error,4(%rsp)
         jmp   handle_exception
 
 ENTRY(coprocessor_error)
+        ENDBR64
         pushq $0
         movl  $TRAP_copro_error,4(%rsp)
         jmp   handle_exception
 
 ENTRY(simd_coprocessor_error)
+        ENDBR64
         pushq $0
         movl  $TRAP_simd_error,4(%rsp)
         jmp   handle_exception
 
 ENTRY(device_not_available)
+        ENDBR64
         pushq $0
         movl  $TRAP_no_device,4(%rsp)
         jmp   handle_exception
 
 ENTRY(debug)
+        ENDBR64
         pushq $0
         movl  $TRAP_debug,4(%rsp)
         jmp   handle_ist_exception
 
 ENTRY(int3)
+        ENDBR64
         pushq $0
         movl  $TRAP_int3,4(%rsp)
         jmp   handle_exception
 
 ENTRY(overflow)
+        ENDBR64
         pushq $0
         movl  $TRAP_overflow,4(%rsp)
         jmp   handle_exception
 
 ENTRY(bounds)
+        ENDBR64
         pushq $0
         movl  $TRAP_bounds,4(%rsp)
         jmp   handle_exception
 
 ENTRY(invalid_op)
+        ENDBR64
         pushq $0
         movl  $TRAP_invalid_op,4(%rsp)
         jmp   handle_exception
 
 ENTRY(invalid_TSS)
+        ENDBR64
         movl  $TRAP_invalid_tss,4(%rsp)
         jmp   handle_exception
 
 ENTRY(segment_not_present)
+        ENDBR64
         movl  $TRAP_no_segment,4(%rsp)
         jmp   handle_exception
 
 ENTRY(stack_segment)
+        ENDBR64
         movl  $TRAP_stack_error,4(%rsp)
         jmp   handle_exception
 
 ENTRY(general_protection)
+        ENDBR64
         movl  $TRAP_gp_fault,4(%rsp)
         jmp   handle_exception
 
 ENTRY(alignment_check)
+        ENDBR64
         movl  $TRAP_alignment_check,4(%rsp)
         jmp   handle_exception
 
 ENTRY(entry_CP)
+        ENDBR64
         movl  $X86_EXC_CP, 4(%rsp)
         jmp   handle_exception
 
 ENTRY(double_fault)
+        ENDBR64
         movl  $TRAP_double_fault,4(%rsp)
         /* Set AC to reduce chance of further SMAP faults */
         ALTERNATIVE "", stac, X86_FEATURE_XEN_SMAP
@@ -966,6 +984,7 @@ ENTRY(double_fault)
 
         .pushsection .init.text, "ax", @progbits
 ENTRY(early_page_fault)
+        ENDBR64
         movl  $TRAP_page_fault,4(%rsp)
         SAVE_ALL
         movq  %rsp,%rdi
@@ -974,6 +993,7 @@ ENTRY(early_page_fault)
         .popsection
 
 ENTRY(nmi)
+        ENDBR64
         pushq $0
         movl  $TRAP_nmi,4(%rsp)
 handle_ist_exception:
@@ -1102,12 +1122,14 @@ handle_ist_exception:
 #endif
 
 ENTRY(machine_check)
+        ENDBR64
         pushq $0
         movl  $TRAP_machine_check,4(%rsp)
         jmp   handle_ist_exception
 
 /* No op trap handler.  Required for kexec crash path. */
 GLOBAL(trap_nop)
+        ENDBR64
         iretq
 
 /* Table of automatically generated entry points.  One per vector. */
@@ -1136,7 +1158,9 @@ autogen_stubs: /* Automatically generated stubs. */
 #endif
 
         ALIGN
-1:      pushq $0
+1:
+        ENDBR64
+        pushq $0
         movb  $vec,4(%rsp)
         jmp   common_interrupt
 
@@ -1146,7 +1170,9 @@ autogen_stubs: /* Automatically generated stubs. */
         .elseif vec == X86_EXC_CSO || vec == X86_EXC_SPV || \
                 vec == X86_EXC_VE  || (vec > X86_EXC_CP && vec < TRAP_nr)
 
-1:      test  $8,%spl        /* 64bit exception frames are 16 byte aligned, 
but the word */
+1:
+        ENDBR64
+        test  $8,%spl        /* 64bit exception frames are 16 byte aligned, 
but the word */
         jz    2f             /* size is 8 bytes.  Check whether the processor 
gave us an */
         pushq $0             /* error code, and insert an empty one if not.    
          */
 2:      movb  $vec,4(%rsp)
-- 
2.11.0