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Diffstat (limited to 'arch/x86/include/asm/nospec-branch.h')
-rw-r--r--arch/x86/include/asm/nospec-branch.h92
1 files changed, 51 insertions, 41 deletions
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index e64fd20778b6..c936ce9f0c47 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -35,33 +35,56 @@
#define RSB_CLEAR_LOOPS 32 /* To forcibly overwrite all entries */
/*
+ * Common helper for __FILL_RETURN_BUFFER and __FILL_ONE_RETURN.
+ */
+#define __FILL_RETURN_SLOT \
+ ANNOTATE_INTRA_FUNCTION_CALL; \
+ call 772f; \
+ int3; \
+772:
+
+/*
+ * Stuff the entire RSB.
+ *
* Google experimented with loop-unrolling and this turned out to be
* the optimal version - two calls, each with their own speculation
* trap should their return address end up getting used, in a loop.
*/
-#define __FILL_RETURN_BUFFER(reg, nr, sp) \
- mov $(nr/2), reg; \
-771: \
- ANNOTATE_INTRA_FUNCTION_CALL; \
- call 772f; \
-773: /* speculation trap */ \
- UNWIND_HINT_EMPTY; \
- pause; \
- lfence; \
- jmp 773b; \
-772: \
- ANNOTATE_INTRA_FUNCTION_CALL; \
- call 774f; \
-775: /* speculation trap */ \
- UNWIND_HINT_EMPTY; \
- pause; \
- lfence; \
- jmp 775b; \
-774: \
- add $(BITS_PER_LONG/8) * 2, sp; \
- dec reg; \
- jnz 771b; \
- /* barrier for jnz misprediction */ \
+#ifdef CONFIG_X86_64
+#define __FILL_RETURN_BUFFER(reg, nr) \
+ mov $(nr/2), reg; \
+771: \
+ __FILL_RETURN_SLOT \
+ __FILL_RETURN_SLOT \
+ add $(BITS_PER_LONG/8) * 2, %_ASM_SP; \
+ dec reg; \
+ jnz 771b; \
+ /* barrier for jnz misprediction */ \
+ lfence;
+#else
+/*
+ * i386 doesn't unconditionally have LFENCE, as such it can't
+ * do a loop.
+ */
+#define __FILL_RETURN_BUFFER(reg, nr) \
+ .rept nr; \
+ __FILL_RETURN_SLOT; \
+ .endr; \
+ add $(BITS_PER_LONG/8) * nr, %_ASM_SP;
+#endif
+
+/*
+ * Stuff a single RSB slot.
+ *
+ * To mitigate Post-Barrier RSB speculation, one CALL instruction must be
+ * forced to retire before letting a RET instruction execute.
+ *
+ * On PBRSB-vulnerable CPUs, it is not safe for a RET to be executed
+ * before this point.
+ */
+#define __FILL_ONE_RETURN \
+ __FILL_RETURN_SLOT \
+ add $(BITS_PER_LONG/8), %_ASM_SP; \
lfence;
#ifdef __ASSEMBLY__
@@ -132,28 +155,15 @@
#endif
.endm
-.macro ISSUE_UNBALANCED_RET_GUARD
- ANNOTATE_INTRA_FUNCTION_CALL
- call .Lunbalanced_ret_guard_\@
- int3
-.Lunbalanced_ret_guard_\@:
- add $(BITS_PER_LONG/8), %_ASM_SP
- lfence
-.endm
-
/*
* A simpler FILL_RETURN_BUFFER macro. Don't make people use the CPP
* monstrosity above, manually.
*/
-.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req ftr2
-.ifb \ftr2
- ALTERNATIVE "jmp .Lskip_rsb_\@", "", \ftr
-.else
- ALTERNATIVE_2 "jmp .Lskip_rsb_\@", "", \ftr, "jmp .Lunbalanced_\@", \ftr2
-.endif
- __FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP)
-.Lunbalanced_\@:
- ISSUE_UNBALANCED_RET_GUARD
+.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req ftr2=ALT_NOT(X86_FEATURE_ALWAYS)
+ ALTERNATIVE_2 "jmp .Lskip_rsb_\@", \
+ __stringify(__FILL_RETURN_BUFFER(\reg,\nr)), \ftr, \
+ __stringify(__FILL_ONE_RETURN), \ftr2
+
.Lskip_rsb_\@:
.endm