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authorPeter Zijlstra <peterz@infradead.org>2020-04-16 14:34:26 +0200
committerPeter Zijlstra <peterz@infradead.org>2020-04-30 20:14:34 +0200
commitcc1ac9c792810b93783a7de344f428922af8d98c (patch)
tree33da496a06b118211f1178a55f3d30d51f96abec /arch/x86/lib
parent34fdce6981b96920ced4e0ee56e9db3fb03a33f0 (diff)
downloadlinux-cc1ac9c792810b93783a7de344f428922af8d98c.tar.bz2
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
Diffstat (limited to 'arch/x86/lib')
-rw-r--r--arch/x86/lib/retpoline.S26
1 files changed, 23 insertions, 3 deletions
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 9cc5480300c9..b4c43a9b1483 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -7,15 +7,31 @@
#include <asm/alternative-asm.h>
#include <asm/export.h>
#include <asm/nospec-branch.h>
+#include <asm/unwind_hints.h>
+#include <asm/frame.h>
.macro THUNK reg
.section .text.__x86.indirect_thunk
+ .align 32
SYM_FUNC_START(__x86_indirect_thunk_\reg)
- CFI_STARTPROC
- JMP_NOSPEC %\reg
- CFI_ENDPROC
+ JMP_NOSPEC \reg
SYM_FUNC_END(__x86_indirect_thunk_\reg)
+
+SYM_FUNC_START_NOALIGN(__x86_retpoline_\reg)
+ ANNOTATE_INTRA_FUNCTION_CALL
+ call .Ldo_rop_\@
+.Lspec_trap_\@:
+ UNWIND_HINT_EMPTY
+ pause
+ lfence
+ jmp .Lspec_trap_\@
+.Ldo_rop_\@:
+ mov %\reg, (%_ASM_SP)
+ UNWIND_HINT_RET_OFFSET
+ ret
+SYM_FUNC_END(__x86_retpoline_\reg)
+
.endm
/*
@@ -32,6 +48,7 @@ SYM_FUNC_END(__x86_indirect_thunk_\reg)
#define __EXPORT_THUNK(sym) _ASM_NOKPROBE(sym); EXPORT_SYMBOL(sym)
#define EXPORT_THUNK(reg) __EXPORT_THUNK(__x86_indirect_thunk_ ## reg)
+#define EXPORT_RETPOLINE(reg) __EXPORT_THUNK(__x86_retpoline_ ## reg)
#undef GEN
#define GEN(reg) THUNK reg
@@ -41,3 +58,6 @@ SYM_FUNC_END(__x86_indirect_thunk_\reg)
#define GEN(reg) EXPORT_THUNK(reg)
#include <asm/GEN-for-each-reg.h>
+#undef GEN
+#define GEN(reg) EXPORT_RETPOLINE(reg)
+#include <asm/GEN-for-each-reg.h>