x86/retpoline: Fix retpoline unwind
Currently objtool cannot understand retpolines, and thus cannot generate ORC unwind information for them. This means that we cannot unwind from the middle of a retpoline. The recent ANNOTATE_INTRA_FUNCTION_CALL and UNWIND_HINT_RET_OFFSET support in objtool enables it to understand the basic retpoline construct. A further problem is that the ORC unwind information is alternative invariant; IOW. every alternative should have the same ORC, retpolines obviously violate this. This means we need to out-of-line them. Since all GCC generated code already uses out-of-line retpolines, this should not affect performance much, if anything. This will enable objtool to generate valid ORC data for the out-of-line copies, which means we can correctly and reliably unwind through a retpoline. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Link: https://lkml.kernel.org/r/20200428191700.210835357@infradead.org
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@@ -7,15 +7,31 @@
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#include <asm/alternative-asm.h>
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#include <asm/export.h>
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#include <asm/nospec-branch.h>
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#include <asm/unwind_hints.h>
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#include <asm/frame.h>
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.macro THUNK reg
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.section .text.__x86.indirect_thunk
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.align 32
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SYM_FUNC_START(__x86_indirect_thunk_\reg)
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CFI_STARTPROC
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JMP_NOSPEC %\reg
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CFI_ENDPROC
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JMP_NOSPEC \reg
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SYM_FUNC_END(__x86_indirect_thunk_\reg)
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SYM_FUNC_START_NOALIGN(__x86_retpoline_\reg)
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ANNOTATE_INTRA_FUNCTION_CALL
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call .Ldo_rop_\@
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.Lspec_trap_\@:
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UNWIND_HINT_EMPTY
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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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UNWIND_HINT_RET_OFFSET
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ret
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SYM_FUNC_END(__x86_retpoline_\reg)
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.endm
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/*
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@@ -32,6 +48,7 @@ SYM_FUNC_END(__x86_indirect_thunk_\reg)
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#define __EXPORT_THUNK(sym) _ASM_NOKPROBE(sym); EXPORT_SYMBOL(sym)
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#define EXPORT_THUNK(reg) __EXPORT_THUNK(__x86_indirect_thunk_ ## reg)
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#define EXPORT_RETPOLINE(reg) __EXPORT_THUNK(__x86_retpoline_ ## reg)
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#undef GEN
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#define GEN(reg) THUNK reg
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@@ -41,3 +58,6 @@ SYM_FUNC_END(__x86_indirect_thunk_\reg)
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#define GEN(reg) EXPORT_THUNK(reg)
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#include <asm/GEN-for-each-reg.h>
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#undef GEN
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#define GEN(reg) EXPORT_RETPOLINE(reg)
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#include <asm/GEN-for-each-reg.h>
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