[xen stable-4.16] x86/emul: Update emulation stubs to be CET-IBT compatible

[patchbot@xxxxxxx]

commit 135521e6d7bcb5ccf98f0698307df4f945ca7950
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Nov 1 10:09:59 2021 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Mar 25 17:06:38 2022 +0000

    x86/emul: Update emulation stubs to be CET-IBT compatible
    
    All indirect branches need to land on an endbr64 instruction.
    
    For stub_selftests(), use endbr64 unconditionally for simplicity.  For 
ioport
    and instruction emulation, add endbr64 conditionally.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit 0d101568d29e8b4bfd33f20031fedec2652aa0cf)
---
 xen/arch/x86/extable.c         | 12 +++++++-----
 xen/arch/x86/pv/emul-priv-op.c |  7 +++++++
 xen/arch/x86/x86_emulate.c     | 13 +++++++++++--
 3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/extable.c b/xen/arch/x86/extable.c
index 109ab7da98..0d30595ea1 100644
--- a/xen/arch/x86/extable.c
+++ b/xen/arch/x86/extable.c
@@ -127,20 +127,22 @@ search_exception_table(const struct cpu_user_regs *regs)
 static int __init stub_selftest(void)
 {
     static const struct {
-        uint8_t opc[4];
+        uint8_t opc[8];
         uint64_t rax;
         union stub_exception_token res;
     } tests[] __initconst = {
-        { .opc = { 0x0f, 0xb9, 0xc3, 0xc3 }, /* ud1 */
+#define endbr64 0xf3, 0x0f, 0x1e, 0xfa
+        { .opc = { endbr64, 0x0f, 0xb9, 0xc3, 0xc3 }, /* ud1 */
           .res.fields.trapnr = TRAP_invalid_op },
-        { .opc = { 0x90, 0x02, 0x00, 0xc3 }, /* nop; add (%rax),%al */
+        { .opc = { endbr64, 0x90, 0x02, 0x00, 0xc3 }, /* nop; add (%rax),%al */
           .rax = 0x0123456789abcdef,
           .res.fields.trapnr = TRAP_gp_fault },
-        { .opc = { 0x02, 0x04, 0x04, 0xc3 }, /* add (%rsp,%rax),%al */
+        { .opc = { endbr64, 0x02, 0x04, 0x04, 0xc3 }, /* add (%rsp,%rax),%al */
           .rax = 0xfedcba9876543210,
           .res.fields.trapnr = TRAP_stack_error },
-        { .opc = { 0xcc, 0xc3, 0xc3, 0xc3 }, /* int3 */
+        { .opc = { endbr64, 0xcc, 0xc3, 0xc3, 0xc3 }, /* int3 */
           .res.fields.trapnr = TRAP_int3 },
+#undef endbr64
     };
     unsigned long addr = this_cpu(stubs.addr) + STUB_BUF_SIZE / 2;
     unsigned int i;
diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index 7f4279a051..b73e698cbc 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -26,6 +26,7 @@
 
 #include <asm/amd.h>
 #include <asm/debugreg.h>
+#include <asm/endbr.h>
 #include <asm/hpet.h>
 #include <asm/hypercall.h>
 #include <asm/mc146818rtc.h>
@@ -111,6 +112,12 @@ static io_emul_stub_t *io_emul_stub_setup(struct 
priv_op_ctxt *ctxt, u8 opcode,
 
     p = ctxt->io_emul_stub;
 
+    if ( cpu_has_xen_ibt )
+    {
+        place_endbr64(p);
+        p += 4;
+    }
+
     APPEND_BUFF(prologue);
     APPEND_CALL(load_guest_gprs);
 
diff --git a/xen/arch/x86/x86_emulate.c b/xen/arch/x86/x86_emulate.c
index 1e082e6f3b..379e889768 100644
--- a/xen/arch/x86/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate.c
@@ -17,6 +17,7 @@
 #include <asm/xstate.h>
 #include <asm/amd.h> /* cpu_has_amd_erratum() */
 #include <asm/debugreg.h>
+#include <asm/endbr.h>
 
 /* Avoid namespace pollution. */
 #undef cmpxchg
@@ -29,11 +30,19 @@
         cpu_has_amd_erratum(&current_cpu_data, AMD_ERRATUM_##nr)
 
 #define get_stub(stb) ({                                        \
+    void *ptr;                                                  \
     BUILD_BUG_ON(STUB_BUF_SIZE / 2 < MAX_INST_LEN + 1);         \
     ASSERT(!(stb).ptr);                                         \
     (stb).addr = this_cpu(stubs.addr) + STUB_BUF_SIZE / 2;      \
-    memset(((stb).ptr = map_domain_page(_mfn(this_cpu(stubs.mfn)))) +  \
-           ((stb).addr & ~PAGE_MASK), 0xcc, STUB_BUF_SIZE / 2);        \
+    (stb).ptr = map_domain_page(_mfn(this_cpu(stubs.mfn))) +    \
+        ((stb).addr & ~PAGE_MASK);                              \
+    ptr = memset((stb).ptr, 0xcc, STUB_BUF_SIZE / 2);           \
+    if ( cpu_has_xen_ibt )                                      \
+    {                                                           \
+        place_endbr64(ptr);                                     \
+        ptr += 4;                                               \
+    }                                                           \
+    ptr;                                                        \
 })
 #define put_stub(stb) ({                                   \
     if ( (stb).ptr )                                       \
--
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