@@ -252,8 +252,7 @@ ENTRY(__switch_to_asm)
* exist, overwrite the RSB with entries which capture
* speculative execution to prevent attack.
*/
- /* Clobbers %ebx */
- FILL_RETURN_BUFFER RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
+ FILL_RETURN_BUFFER %ebx, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
#endif
/* restore callee-saved registers */
@@ -364,8 +364,7 @@ ENTRY(__switch_to_asm)
* exist, overwrite the RSB with entries which capture
* speculative execution to prevent attack.
*/
- /* Clobbers %rbx */
- FILL_RETURN_BUFFER RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
+ FILL_RETURN_BUFFER %r12, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
#endif
/* restore callee-saved registers */
@@ -38,7 +38,4 @@ INDIRECT_THUNK(dx)
INDIRECT_THUNK(si)
INDIRECT_THUNK(di)
INDIRECT_THUNK(bp)
-asmlinkage void __fill_rsb(void);
-asmlinkage void __clear_rsb(void);
-
#endif /* CONFIG_RETPOLINE */
@@ -8,6 +8,50 @@
#include <asm/cpufeatures.h>
#include <asm/msr-index.h>
+/*
+ * Fill the CPU return stack buffer.
+ *
+ * Each entry in the RSB, if used for a speculative 'ret', contains an
+ * infinite 'pause; lfence; jmp' loop to capture speculative execution.
+ *
+ * This is required in various cases for retpoline and IBRS-based
+ * mitigations for the Spectre variant 2 vulnerability. Sometimes to
+ * eliminate potentially bogus entries from the RSB, and sometimes
+ * purely to ensure that it doesn't get empty, which on some CPUs would
+ * allow predictions from other (unwanted!) sources to be used.
+ *
+ * We define a CPP macro such that it can be used from both .S files and
+ * inline assembly. It's possible to do a .macro and then include that
+ * from C via asm(".include <asm/nospec-branch.h>") but let's not go there.
+ */
+
+#define RSB_CLEAR_LOOPS 32 /* To forcibly overwrite all entries */
+#define RSB_FILL_LOOPS 16 /* To avoid underflow */
+
+/*
+ * 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: \
+ call 772f; \
+773: /* speculation trap */ \
+ pause; \
+ lfence; \
+ jmp 773b; \
+772: \
+ call 774f; \
+775: /* speculation trap */ \
+ pause; \
+ lfence; \
+ jmp 775b; \
+774: \
+ dec reg; \
+ jnz 771b; \
+ add $(BITS_PER_LONG/8) * nr, sp;
+
#ifdef __ASSEMBLY__
/*
@@ -78,10 +122,17 @@
#endif
.endm
-/* This clobbers the BX register */
-.macro FILL_RETURN_BUFFER nr:req ftr:req
+ /*
+ * A simpler FILL_RETURN_BUFFER macro. Don't make people use the CPP
+ * monstrosity above, manually.
+ */
+.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req
#ifdef CONFIG_RETPOLINE
- ALTERNATIVE "", "call __clear_rsb", \ftr
+ ANNOTATE_NOSPEC_ALTERNATIVE
+ ALTERNATIVE "jmp .Lskip_rsb_\@", \
+ __stringify(__FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP)) \
+ \ftr
+.Lskip_rsb_\@:
#endif
.endm
@@ -156,10 +207,15 @@ extern char __indirect_thunk_end[];
static inline void vmexit_fill_RSB(void)
{
#ifdef CONFIG_RETPOLINE
- alternative_input("",
- "call __fill_rsb",
- X86_FEATURE_RETPOLINE,
- ASM_NO_INPUT_CLOBBER(_ASM_BX, "memory"));
+ unsigned long loops;
+
+ asm volatile (ANNOTATE_NOSPEC_ALTERNATIVE
+ ALTERNATIVE("jmp 910f",
+ __stringify(__FILL_RETURN_BUFFER(%0, RSB_CLEAR_LOOPS, %1)),
+ X86_FEATURE_RETPOLINE)
+ "910:"
+ : "=r" (loops), ASM_CALL_CONSTRAINT
+ : : "memory" );
#endif
}
@@ -27,7 +27,6 @@ lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) +=
lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o insn-eval.o
lib-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
lib-$(CONFIG_RETPOLINE) += retpoline.o
-OBJECT_FILES_NON_STANDARD_retpoline.o :=y
obj-y += msr.o msr-reg.o msr-reg-export.o hweight.o
@@ -7,7 +7,6 @@
#include <asm/alternative-asm.h>
#include <asm/export.h>
#include <asm/nospec-branch.h>
-#include <asm/bitsperlong.h>
.macro THUNK reg
.section .text.__x86.indirect_thunk
@@ -47,58 +46,3 @@ GENERATE_THUNK(r13)
GENERATE_THUNK(r14)
GENERATE_THUNK(r15)
#endif
-
-/*
- * Fill the CPU return stack buffer.
- *
- * Each entry in the RSB, if used for a speculative 'ret', contains an
- * infinite 'pause; lfence; jmp' loop to capture speculative execution.
- *
- * This is required in various cases for retpoline and IBRS-based
- * mitigations for the Spectre variant 2 vulnerability. Sometimes to
- * eliminate potentially bogus entries from the RSB, and sometimes
- * purely to ensure that it doesn't get empty, which on some CPUs would
- * allow predictions from other (unwanted!) sources to be used.
- *
- * 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.
- */
-.macro STUFF_RSB nr:req sp:req
- mov $(\nr / 2), %_ASM_BX
- .align 16
-771:
- call 772f
-773: /* speculation trap */
- pause
- lfence
- jmp 773b
- .align 16
-772:
- call 774f
-775: /* speculation trap */
- pause
- lfence
- jmp 775b
- .align 16
-774:
- dec %_ASM_BX
- jnz 771b
- add $((BITS_PER_LONG/8) * \nr), \sp
-.endm
-
-#define RSB_FILL_LOOPS 16 /* To avoid underflow */
-
-ENTRY(__fill_rsb)
- STUFF_RSB RSB_FILL_LOOPS, %_ASM_SP
- ret
-END(__fill_rsb)
-EXPORT_SYMBOL_GPL(__fill_rsb)
-
-#define RSB_CLEAR_LOOPS 32 /* To forcibly overwrite all entries */
-
-ENTRY(__clear_rsb)
- STUFF_RSB RSB_CLEAR_LOOPS, %_ASM_SP
- ret
-END(__clear_rsb)
-EXPORT_SYMBOL_GPL(__clear_rsb)