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x86/retpoline: Fix retpoline unwind

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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
This commit is contained in:
Peter Zijlstra 2020-04-16 14:34:26 +02:00
parent 34fdce6981
commit cc1ac9c792
3 changed files with 38 additions and 51 deletions
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7
arch/x86/include/asm/asm-prototypes.h
View file

@ -21,8 +21,15 @@ extern void cmpxchg8b_emu(void);
#define DECL_INDIRECT_THUNK(reg) \
extern asmlinkage void __x86_indirect_thunk_ ## reg (void);
#define DECL_RETPOLINE(reg) \
extern asmlinkage void __x86_retpoline_ ## reg (void);
#undef GEN
#define GEN(reg) DECL_INDIRECT_THUNK(reg)
#include <asm/GEN-for-each-reg.h>
#undef GEN
#define GEN(reg) DECL_RETPOLINE(reg)
#include <asm/GEN-for-each-reg.h>
#endif /* CONFIG_RETPOLINE */

56
arch/x86/include/asm/nospec-branch.h
View file

@ -12,15 +12,6 @@
#include <asm/msr-index.h>
#include <asm/unwind_hints.h>
/*
* This should be used immediately before a retpoline alternative. It tells
* objtool where the retpolines are so that it can make sense of the control
* flow by just reading the original instruction(s) and ignoring the
* alternatives.
*/
#define ANNOTATE_NOSPEC_ALTERNATIVE \
ANNOTATE_IGNORE_ALTERNATIVE
/*
* Fill the CPU return stack buffer.
*
@ -82,34 +73,6 @@
.popsection
.endm
/*
* These are the bare retpoline primitives for indirect jmp and call.
* Do not use these directly; they only exist to make the ALTERNATIVE
* invocation below less ugly.
*/
.macro RETPOLINE_JMP reg:req
call .Ldo_rop_\@
.Lspec_trap_\@:
pause
lfence
jmp .Lspec_trap_\@
.Ldo_rop_\@:
mov \reg, (%_ASM_SP)
ret
.endm
/*
* This is a wrapper around RETPOLINE_JMP so the called function in reg
* returns to the instruction after the macro.
*/
.macro RETPOLINE_CALL reg:req
jmp .Ldo_call_\@
.Ldo_retpoline_jmp_\@:
RETPOLINE_JMP \reg
.Ldo_call_\@:
call .Ldo_retpoline_jmp_\@
.endm
/*
* JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple
* indirect jmp/call which may be susceptible to the Spectre variant 2
@ -117,10 +80,9 @@
*/
.macro JMP_NOSPEC reg:req
#ifdef CONFIG_RETPOLINE
ANNOTATE_NOSPEC_ALTERNATIVE
ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
__stringify(RETPOLINE_JMP %\reg), X86_FEATURE_RETPOLINE,\
__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD
ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
__stringify(jmp __x86_retpoline_\reg), X86_FEATURE_RETPOLINE, \
__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD
#else
jmp *%\reg
#endif
@ -128,10 +90,9 @@
.macro CALL_NOSPEC reg:req
#ifdef CONFIG_RETPOLINE
ANNOTATE_NOSPEC_ALTERNATIVE
ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg),\
__stringify(RETPOLINE_CALL %\reg), X86_FEATURE_RETPOLINE,\
__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_AMD
ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \
__stringify(call __x86_retpoline_\reg), X86_FEATURE_RETPOLINE, \
__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_AMD
#else
call *%\reg
#endif
@ -165,16 +126,16 @@
* which is ensured when CONFIG_RETPOLINE is defined.
*/
# define CALL_NOSPEC \
ANNOTATE_NOSPEC_ALTERNATIVE \
ALTERNATIVE_2( \
ANNOTATE_RETPOLINE_SAFE \
"call *%[thunk_target]\n", \
"call __x86_indirect_thunk_%V[thunk_target]\n", \
"call __x86_retpoline_%V[thunk_target]\n", \
X86_FEATURE_RETPOLINE, \
"lfence;\n" \
ANNOTATE_RETPOLINE_SAFE \
"call *%[thunk_target]\n", \
X86_FEATURE_RETPOLINE_AMD)
# define THUNK_TARGET(addr) [thunk_target] "r" (addr)
#else /* CONFIG_X86_32 */
@ -184,7 +145,6 @@
* here, anyway.
*/
# define CALL_NOSPEC \
ANNOTATE_NOSPEC_ALTERNATIVE \
ALTERNATIVE_2( \
ANNOTATE_RETPOLINE_SAFE \
"call *%[thunk_target]\n", \

26
arch/x86/lib/retpoline.S
View file

@ -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>