forked from luck/tmp_suning_uos_patched
x86/retpoline: Simplify retpolines
commit 119251855f9adf9421cb5eb409933092141ab2c7 upstream.
Due to:
c9c324dc22aa ("objtool: Support stack layout changes in alternatives")
it is now possible to simplify the retpolines.
Currently our retpolines consist of 2 symbols:
- __x86_indirect_thunk_\reg: the compiler target
- __x86_retpoline_\reg: the actual retpoline.
Both are consecutive in code and aligned such that for any one register
they both live in the same cacheline:
0000000000000000 <__x86_indirect_thunk_rax>:
0: ff e0 jmpq *%rax
2: 90 nop
3: 90 nop
4: 90 nop
0000000000000005 <__x86_retpoline_rax>:
5: e8 07 00 00 00 callq 11 <__x86_retpoline_rax+0xc>
a: f3 90 pause
c: 0f ae e8 lfence
f: eb f9 jmp a <__x86_retpoline_rax+0x5>
11: 48 89 04 24 mov %rax,(%rsp)
15: c3 retq
16: 66 2e 0f 1f 84 00 00 00 00 00 nopw %cs:0x0(%rax,%rax,1)
The thunk is an alternative_2, where one option is a JMP to the
retpoline. This was done so that objtool didn't need to deal with
alternatives with stack ops. But that problem has been solved, so now
it is possible to fold the entire retpoline into the alternative to
simplify and consolidate unused bytes:
0000000000000000 <__x86_indirect_thunk_rax>:
0: ff e0 jmpq *%rax
2: 90 nop
3: 90 nop
4: 90 nop
5: 90 nop
6: 90 nop
7: 90 nop
8: 90 nop
9: 90 nop
a: 90 nop
b: 90 nop
c: 90 nop
d: 90 nop
e: 90 nop
f: 90 nop
10: 90 nop
11: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw %cs:0x0(%rax,%rax,1)
1c: 0f 1f 40 00 nopl 0x0(%rax)
Notice that since the longest alternative sequence is now:
0: e8 07 00 00 00 callq c <.altinstr_replacement+0xc>
5: f3 90 pause
7: 0f ae e8 lfence
a: eb f9 jmp 5 <.altinstr_replacement+0x5>
c: 48 89 04 24 mov %rax,(%rsp)
10: c3 retq
17 bytes, we have 15 bytes NOP at the end of our 32 byte slot. (IOW, if
we can shrink the retpoline by 1 byte we can pack it more densely).
[ bp: Massage commit message. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210326151259.506071949@infradead.org
[bwh: Backported to 5.10:
- Use X86_FEATRURE_RETPOLINE_LFENCE flag instead of
X86_FEATURE_RETPOLINE_AMD, since the later renaming of this flag
has already been applied
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Zijlstra
Greg Kroah-Hartman
parent
e68db6f780
commit
28ca351296
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@ -22,15 +22,8 @@ extern void cmpxchg8b_emu(void);
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#define DECL_INDIRECT_THUNK(reg) \
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extern asmlinkage void __x86_indirect_thunk_ ## reg (void);
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#define DECL_RETPOLINE(reg) \
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extern asmlinkage void __x86_retpoline_ ## reg (void);
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#undef GEN
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#define GEN(reg) DECL_INDIRECT_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) DECL_RETPOLINE(reg)
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#include <asm/GEN-for-each-reg.h>
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#endif /* CONFIG_RETPOLINE */
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@ -80,7 +80,7 @@
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.macro JMP_NOSPEC reg:req
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#ifdef CONFIG_RETPOLINE
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ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
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__stringify(jmp __x86_retpoline_\reg), X86_FEATURE_RETPOLINE, \
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__stringify(jmp __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \
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__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_LFENCE
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#else
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jmp *%\reg
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@ -90,7 +90,7 @@
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.macro CALL_NOSPEC reg:req
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#ifdef CONFIG_RETPOLINE
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ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \
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__stringify(call __x86_retpoline_\reg), X86_FEATURE_RETPOLINE, \
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__stringify(call __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \
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__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_LFENCE
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#else
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call *%\reg
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@ -128,7 +128,7 @@
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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_retpoline_%V[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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@ -10,27 +10,31 @@
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#include <asm/unwind_hints.h>
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#include <asm/frame.h>
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.macro 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_FUNC
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ret
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.endm
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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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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_FUNC
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ret
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SYM_FUNC_END(__x86_retpoline_\reg)
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ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
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__stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \
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__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_LFENCE
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SYM_FUNC_END(__x86_indirect_thunk_\reg)
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.endm
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@ -48,7 +52,6 @@ SYM_FUNC_END(__x86_retpoline_\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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@ -58,6 +61,3 @@ SYM_FUNC_END(__x86_retpoline_\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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@ -800,8 +800,7 @@ static int add_jump_destinations(struct objtool_file *file)
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} else if (reloc->sym->type == STT_SECTION) {
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dest_sec = reloc->sym->sec;
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dest_off = arch_dest_reloc_offset(reloc->addend);
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} else if (!strncmp(reloc->sym->name, "__x86_indirect_thunk_", 21) ||
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!strncmp(reloc->sym->name, "__x86_retpoline_", 16)) {
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} else if (!strncmp(reloc->sym->name, "__x86_indirect_thunk_", 21)) {
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/*
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* Retpoline jumps are really dynamic jumps in
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* disguise, so convert them accordingly.
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