07f07f55a2
Add a static key which controls the invocation of the CPU buffer clear mechanism on idle entry. This is independent of other MDS mitigations because the idle entry invocation to mitigate the potential leakage due to store buffer repartitioning is only necessary on SMT systems. Add the actual invocations to the different halt/mwait variants which covers all usage sites. mwaitx is not patched as it's not available on Intel CPUs. The buffer clear is only invoked before entering the C-State to prevent that stale data from the idling CPU is spilled to the Hyper-Thread sibling after the Store buffer got repartitioned and all entries are available to the non idle sibling. When coming out of idle the store buffer is partitioned again so each sibling has half of it available. Now CPU which returned from idle could be speculatively exposed to contents of the sibling, but the buffers are flushed either on exit to user space or on VMENTER. When later on conditional buffer clearing is implemented on top of this, then there is no action required either because before returning to user space the context switch will set the condition flag which causes a flush on the return to user path. Note, that the buffer clearing on idle is only sensible on CPUs which are solely affected by MSBDS and not any other variant of MDS because the other MDS variants cannot be mitigated when SMT is enabled, so the buffer clearing on idle would be a window dressing exercise. This intentionally does not handle the case in the acpi/processor_idle driver which uses the legacy IO port interface for C-State transitions for two reasons: - The acpi/processor_idle driver was replaced by the intel_idle driver almost a decade ago. Anything Nehalem upwards supports it and defaults to that new driver. - The legacy IO port interface is likely to be used on older and therefore unaffected CPUs or on systems which do not receive microcode updates anymore, so there is no point in adding that. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Borislav Petkov <bp@suse.de> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Reviewed-by: Jon Masters <jcm@redhat.com> Tested-by: Jon Masters <jcm@redhat.com>
432 lines
11 KiB
C
432 lines
11 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_NOSPEC_BRANCH_H_
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#define _ASM_X86_NOSPEC_BRANCH_H_
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#include <linux/static_key.h>
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#include <asm/alternative.h>
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#include <asm/alternative-asm.h>
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#include <asm/cpufeatures.h>
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#include <asm/msr-index.h>
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/*
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* Fill the CPU return stack buffer.
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*
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* Each entry in the RSB, if used for a speculative 'ret', contains an
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* infinite 'pause; lfence; jmp' loop to capture speculative execution.
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*
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* This is required in various cases for retpoline and IBRS-based
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* mitigations for the Spectre variant 2 vulnerability. Sometimes to
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* eliminate potentially bogus entries from the RSB, and sometimes
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* purely to ensure that it doesn't get empty, which on some CPUs would
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* allow predictions from other (unwanted!) sources to be used.
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*
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* We define a CPP macro such that it can be used from both .S files and
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* inline assembly. It's possible to do a .macro and then include that
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* from C via asm(".include <asm/nospec-branch.h>") but let's not go there.
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*/
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#define RSB_CLEAR_LOOPS 32 /* To forcibly overwrite all entries */
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#define RSB_FILL_LOOPS 16 /* To avoid underflow */
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/*
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* Google experimented with loop-unrolling and this turned out to be
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* the optimal version — two calls, each with their own speculation
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* trap should their return address end up getting used, in a loop.
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*/
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#define __FILL_RETURN_BUFFER(reg, nr, sp) \
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mov $(nr/2), reg; \
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771: \
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call 772f; \
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773: /* speculation trap */ \
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pause; \
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lfence; \
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jmp 773b; \
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772: \
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call 774f; \
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775: /* speculation trap */ \
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pause; \
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lfence; \
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jmp 775b; \
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774: \
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dec reg; \
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jnz 771b; \
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add $(BITS_PER_LONG/8) * nr, sp;
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#ifdef __ASSEMBLY__
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/*
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* This should be used immediately before a retpoline alternative. It tells
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* objtool where the retpolines are so that it can make sense of the control
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* flow by just reading the original instruction(s) and ignoring the
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* alternatives.
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*/
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.macro ANNOTATE_NOSPEC_ALTERNATIVE
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.Lannotate_\@:
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.pushsection .discard.nospec
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.long .Lannotate_\@ - .
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.popsection
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.endm
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/*
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* This should be used immediately before an indirect jump/call. It tells
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* objtool the subsequent indirect jump/call is vouched safe for retpoline
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* builds.
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*/
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.macro ANNOTATE_RETPOLINE_SAFE
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.Lannotate_\@:
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.pushsection .discard.retpoline_safe
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_ASM_PTR .Lannotate_\@
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.popsection
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.endm
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/*
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* These are the bare retpoline primitives for indirect jmp and call.
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* Do not use these directly; they only exist to make the ALTERNATIVE
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* invocation below less ugly.
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*/
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.macro RETPOLINE_JMP reg:req
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call .Ldo_rop_\@
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.Lspec_trap_\@:
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pause
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lfence
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jmp .Lspec_trap_\@
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.Ldo_rop_\@:
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mov \reg, (%_ASM_SP)
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ret
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.endm
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/*
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* This is a wrapper around RETPOLINE_JMP so the called function in reg
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* returns to the instruction after the macro.
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*/
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.macro RETPOLINE_CALL reg:req
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jmp .Ldo_call_\@
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.Ldo_retpoline_jmp_\@:
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RETPOLINE_JMP \reg
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.Ldo_call_\@:
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call .Ldo_retpoline_jmp_\@
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.endm
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/*
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* JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple
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* indirect jmp/call which may be susceptible to the Spectre variant 2
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* attack.
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*/
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.macro JMP_NOSPEC reg:req
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#ifdef CONFIG_RETPOLINE
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ANNOTATE_NOSPEC_ALTERNATIVE
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ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *\reg), \
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__stringify(RETPOLINE_JMP \reg), X86_FEATURE_RETPOLINE, \
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__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *\reg), X86_FEATURE_RETPOLINE_AMD
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#else
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jmp *\reg
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#endif
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.endm
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.macro CALL_NOSPEC reg:req
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#ifdef CONFIG_RETPOLINE
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ANNOTATE_NOSPEC_ALTERNATIVE
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ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *\reg), \
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__stringify(RETPOLINE_CALL \reg), X86_FEATURE_RETPOLINE,\
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__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *\reg), X86_FEATURE_RETPOLINE_AMD
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#else
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call *\reg
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#endif
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.endm
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/*
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* A simpler FILL_RETURN_BUFFER macro. Don't make people use the CPP
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* monstrosity above, manually.
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*/
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.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req
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#ifdef CONFIG_RETPOLINE
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ANNOTATE_NOSPEC_ALTERNATIVE
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ALTERNATIVE "jmp .Lskip_rsb_\@", \
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__stringify(__FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP)) \
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\ftr
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.Lskip_rsb_\@:
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#endif
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.endm
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#else /* __ASSEMBLY__ */
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#define ANNOTATE_NOSPEC_ALTERNATIVE \
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"999:\n\t" \
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".pushsection .discard.nospec\n\t" \
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".long 999b - .\n\t" \
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".popsection\n\t"
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#define ANNOTATE_RETPOLINE_SAFE \
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"999:\n\t" \
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".pushsection .discard.retpoline_safe\n\t" \
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_ASM_PTR " 999b\n\t" \
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".popsection\n\t"
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#ifdef CONFIG_RETPOLINE
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#ifdef CONFIG_X86_64
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/*
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* Inline asm uses the %V modifier which is only in newer GCC
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* which is ensured when CONFIG_RETPOLINE is defined.
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*/
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# define CALL_NOSPEC \
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ANNOTATE_NOSPEC_ALTERNATIVE \
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ALTERNATIVE_2( \
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ANNOTATE_RETPOLINE_SAFE \
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"call *%[thunk_target]\n", \
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"call __x86_indirect_thunk_%V[thunk_target]\n", \
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X86_FEATURE_RETPOLINE, \
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"lfence;\n" \
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ANNOTATE_RETPOLINE_SAFE \
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"call *%[thunk_target]\n", \
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X86_FEATURE_RETPOLINE_AMD)
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# define THUNK_TARGET(addr) [thunk_target] "r" (addr)
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#else /* CONFIG_X86_32 */
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/*
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* For i386 we use the original ret-equivalent retpoline, because
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* otherwise we'll run out of registers. We don't care about CET
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* here, anyway.
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*/
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# define CALL_NOSPEC \
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ANNOTATE_NOSPEC_ALTERNATIVE \
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ALTERNATIVE_2( \
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ANNOTATE_RETPOLINE_SAFE \
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"call *%[thunk_target]\n", \
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" jmp 904f;\n" \
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" .align 16\n" \
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"901: call 903f;\n" \
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"902: pause;\n" \
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" lfence;\n" \
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" jmp 902b;\n" \
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" .align 16\n" \
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"903: addl $4, %%esp;\n" \
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" pushl %[thunk_target];\n" \
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" ret;\n" \
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" .align 16\n" \
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"904: call 901b;\n", \
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X86_FEATURE_RETPOLINE, \
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"lfence;\n" \
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ANNOTATE_RETPOLINE_SAFE \
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"call *%[thunk_target]\n", \
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X86_FEATURE_RETPOLINE_AMD)
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# define THUNK_TARGET(addr) [thunk_target] "rm" (addr)
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#endif
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#else /* No retpoline for C / inline asm */
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# define CALL_NOSPEC "call *%[thunk_target]\n"
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# define THUNK_TARGET(addr) [thunk_target] "rm" (addr)
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#endif
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/* The Spectre V2 mitigation variants */
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enum spectre_v2_mitigation {
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SPECTRE_V2_NONE,
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SPECTRE_V2_RETPOLINE_GENERIC,
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SPECTRE_V2_RETPOLINE_AMD,
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SPECTRE_V2_IBRS_ENHANCED,
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};
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/* The indirect branch speculation control variants */
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enum spectre_v2_user_mitigation {
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SPECTRE_V2_USER_NONE,
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SPECTRE_V2_USER_STRICT,
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SPECTRE_V2_USER_STRICT_PREFERRED,
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SPECTRE_V2_USER_PRCTL,
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SPECTRE_V2_USER_SECCOMP,
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};
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/* The Speculative Store Bypass disable variants */
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enum ssb_mitigation {
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SPEC_STORE_BYPASS_NONE,
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SPEC_STORE_BYPASS_DISABLE,
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SPEC_STORE_BYPASS_PRCTL,
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SPEC_STORE_BYPASS_SECCOMP,
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};
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extern char __indirect_thunk_start[];
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extern char __indirect_thunk_end[];
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/*
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* On VMEXIT we must ensure that no RSB predictions learned in the guest
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* can be followed in the host, by overwriting the RSB completely. Both
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* retpoline and IBRS mitigations for Spectre v2 need this; only on future
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* CPUs with IBRS_ALL *might* it be avoided.
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*/
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static inline void vmexit_fill_RSB(void)
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{
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#ifdef CONFIG_RETPOLINE
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unsigned long loops;
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asm volatile (ANNOTATE_NOSPEC_ALTERNATIVE
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ALTERNATIVE("jmp 910f",
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__stringify(__FILL_RETURN_BUFFER(%0, RSB_CLEAR_LOOPS, %1)),
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X86_FEATURE_RETPOLINE)
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"910:"
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: "=r" (loops), ASM_CALL_CONSTRAINT
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: : "memory" );
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#endif
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}
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static __always_inline
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void alternative_msr_write(unsigned int msr, u64 val, unsigned int feature)
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{
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asm volatile(ALTERNATIVE("", "wrmsr", %c[feature])
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: : "c" (msr),
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"a" ((u32)val),
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"d" ((u32)(val >> 32)),
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[feature] "i" (feature)
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: "memory");
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}
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static inline void indirect_branch_prediction_barrier(void)
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{
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u64 val = PRED_CMD_IBPB;
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alternative_msr_write(MSR_IA32_PRED_CMD, val, X86_FEATURE_USE_IBPB);
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}
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/* The Intel SPEC CTRL MSR base value cache */
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extern u64 x86_spec_ctrl_base;
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/*
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* With retpoline, we must use IBRS to restrict branch prediction
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* before calling into firmware.
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*
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* (Implemented as CPP macros due to header hell.)
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*/
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#define firmware_restrict_branch_speculation_start() \
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do { \
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u64 val = x86_spec_ctrl_base | SPEC_CTRL_IBRS; \
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\
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preempt_disable(); \
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alternative_msr_write(MSR_IA32_SPEC_CTRL, val, \
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X86_FEATURE_USE_IBRS_FW); \
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} while (0)
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#define firmware_restrict_branch_speculation_end() \
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do { \
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u64 val = x86_spec_ctrl_base; \
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\
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alternative_msr_write(MSR_IA32_SPEC_CTRL, val, \
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X86_FEATURE_USE_IBRS_FW); \
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preempt_enable(); \
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} while (0)
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DECLARE_STATIC_KEY_FALSE(switch_to_cond_stibp);
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DECLARE_STATIC_KEY_FALSE(switch_mm_cond_ibpb);
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DECLARE_STATIC_KEY_FALSE(switch_mm_always_ibpb);
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DECLARE_STATIC_KEY_FALSE(mds_user_clear);
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DECLARE_STATIC_KEY_FALSE(mds_idle_clear);
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#include <asm/segment.h>
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/**
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* mds_clear_cpu_buffers - Mitigation for MDS vulnerability
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*
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* This uses the otherwise unused and obsolete VERW instruction in
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* combination with microcode which triggers a CPU buffer flush when the
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* instruction is executed.
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*/
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static inline void mds_clear_cpu_buffers(void)
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{
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static const u16 ds = __KERNEL_DS;
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/*
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* Has to be the memory-operand variant because only that
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* guarantees the CPU buffer flush functionality according to
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* documentation. The register-operand variant does not.
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* Works with any segment selector, but a valid writable
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* data segment is the fastest variant.
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*
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* "cc" clobber is required because VERW modifies ZF.
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*/
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asm volatile("verw %[ds]" : : [ds] "m" (ds) : "cc");
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}
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/**
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* mds_user_clear_cpu_buffers - Mitigation for MDS vulnerability
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*
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* Clear CPU buffers if the corresponding static key is enabled
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*/
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static inline void mds_user_clear_cpu_buffers(void)
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{
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if (static_branch_likely(&mds_user_clear))
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mds_clear_cpu_buffers();
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}
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/**
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* mds_idle_clear_cpu_buffers - Mitigation for MDS vulnerability
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*
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* Clear CPU buffers if the corresponding static key is enabled
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*/
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static inline void mds_idle_clear_cpu_buffers(void)
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{
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if (static_branch_likely(&mds_idle_clear))
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mds_clear_cpu_buffers();
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}
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#endif /* __ASSEMBLY__ */
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/*
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* Below is used in the eBPF JIT compiler and emits the byte sequence
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* for the following assembly:
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*
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* With retpolines configured:
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*
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* callq do_rop
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* spec_trap:
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* pause
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* lfence
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* jmp spec_trap
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* do_rop:
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* mov %rax,(%rsp) for x86_64
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* mov %edx,(%esp) for x86_32
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* retq
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*
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* Without retpolines configured:
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*
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* jmp *%rax for x86_64
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* jmp *%edx for x86_32
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*/
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#ifdef CONFIG_RETPOLINE
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# ifdef CONFIG_X86_64
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# define RETPOLINE_RAX_BPF_JIT_SIZE 17
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# define RETPOLINE_RAX_BPF_JIT() \
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do { \
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EMIT1_off32(0xE8, 7); /* callq do_rop */ \
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/* spec_trap: */ \
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EMIT2(0xF3, 0x90); /* pause */ \
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EMIT3(0x0F, 0xAE, 0xE8); /* lfence */ \
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EMIT2(0xEB, 0xF9); /* jmp spec_trap */ \
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/* do_rop: */ \
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EMIT4(0x48, 0x89, 0x04, 0x24); /* mov %rax,(%rsp) */ \
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EMIT1(0xC3); /* retq */ \
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} while (0)
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# else /* !CONFIG_X86_64 */
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# define RETPOLINE_EDX_BPF_JIT() \
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do { \
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EMIT1_off32(0xE8, 7); /* call do_rop */ \
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/* spec_trap: */ \
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EMIT2(0xF3, 0x90); /* pause */ \
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EMIT3(0x0F, 0xAE, 0xE8); /* lfence */ \
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EMIT2(0xEB, 0xF9); /* jmp spec_trap */ \
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/* do_rop: */ \
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EMIT3(0x89, 0x14, 0x24); /* mov %edx,(%esp) */ \
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EMIT1(0xC3); /* ret */ \
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} while (0)
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# endif
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#else /* !CONFIG_RETPOLINE */
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# ifdef CONFIG_X86_64
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# define RETPOLINE_RAX_BPF_JIT_SIZE 2
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# define RETPOLINE_RAX_BPF_JIT() \
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EMIT2(0xFF, 0xE0); /* jmp *%rax */
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# else /* !CONFIG_X86_64 */
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# define RETPOLINE_EDX_BPF_JIT() \
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EMIT2(0xFF, 0xE2) /* jmp *%edx */
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# endif
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#endif
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#endif /* _ASM_X86_NOSPEC_BRANCH_H_ */
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