[xen staging] x86: limit amount of INT3 in IND_THUNK_*

[patchbot@xxxxxxx]

commit 9689b1acab71adc2bcc07b3e23c141907dd9ecb8
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Apr 9 09:17:04 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Apr 9 09:17:04 2021 +0200

    x86: limit amount of INT3 in IND_THUNK_*
    
    There's no point having every replacement variant to also specify the
    INT3 - just have it once in the base macro. When patching, NOPs will get
    inserted, which are fine to speculate through (until reaching the INT3).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/indirect-thunk.S | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/indirect-thunk.S b/xen/arch/x86/indirect-thunk.S
index 7392aee127..a090b35dcf 100644
--- a/xen/arch/x86/indirect-thunk.S
+++ b/xen/arch/x86/indirect-thunk.S
@@ -11,6 +11,9 @@
 
 #include <asm/asm_defns.h>
 
+/* Don't transform the "ret" further down. */
+.purgem ret
+
 .macro IND_THUNK_RETPOLINE reg:req
         call 2f
 1:
@@ -24,12 +27,10 @@
 .macro IND_THUNK_LFENCE reg:req
         lfence
         jmp *%\reg
-        int3 /* Halt straight-line speculation */
 .endm
 
 .macro IND_THUNK_JMP reg:req
         jmp *%\reg
-        int3 /* Halt straight-line speculation */
 .endm
 
 /*
@@ -44,6 +45,8 @@ ENTRY(__x86_indirect_thunk_\reg)
         __stringify(IND_THUNK_LFENCE \reg), X86_FEATURE_IND_THUNK_LFENCE, \
         __stringify(IND_THUNK_JMP \reg),    X86_FEATURE_IND_THUNK_JMP
 
+        int3 /* Halt straight-line speculation */
+
         .size __x86_indirect_thunk_\reg, . - __x86_indirect_thunk_\reg
         .type __x86_indirect_thunk_\reg, @function
 .endm
--
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