Messages in this thread Patch in this message | | | Date | Thu, 14 Oct 2021 12:05:46 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 4/9] x86/alternative: Implement .retpoline_sites support |
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On Wed, Oct 13, 2021 at 05:12:13PM +0200, Peter Zijlstra wrote: > On Wed, Oct 13, 2021 at 03:38:27PM +0100, Andrew Cooper wrote: > > On 13/10/2021 13:22, Peter Zijlstra wrote:
> > > +static int patch_retpoline(void *addr, struct insn *insn, u8 *bytes) > > > +{ > > > + void (*target)(void); > > > + int reg, i = 0; > > > + > > > + if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) > > > + return -1; > > > + > > > + target = addr + insn->length + insn->immediate.value; > > > + reg = (target - &__x86_indirect_thunk_rax) / > > > + (&__x86_indirect_thunk_rcx - &__x86_indirect_thunk_rax); > > > > This is equal measures beautiful and terrifying. > > Thanks! :-)
Would something like this appease people? If the toolchain can mess this up everything is broken.
That makes the symtab looks like:
(and arguably, that array symbol could be local)
... 35: 0000000000000000 512 NOTYPE GLOBAL DEFAULT 4 __x86_indirect_thunk_array 36: 0000000000000000 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rax 37: 0000000000000020 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rcx 38: 0000000000000040 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rdx 39: 0000000000000060 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rbx 40: 0000000000000080 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rsp 41: 00000000000000a0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rbp 42: 00000000000000c0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rsi 43: 00000000000000e0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rdi 44: 0000000000000100 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r8 45: 0000000000000120 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r9 46: 0000000000000140 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r10 47: 0000000000000160 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r11 48: 0000000000000180 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r12 49: 00000000000001a0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r13 50: 00000000000001c0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r14 51: 00000000000001e0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r15
--- --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -30,7 +30,7 @@ .align 32 -SYM_FUNC_START(__x86_indirect_thunk_\reg) +SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL) ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \ __stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \ @@ -55,10 +55,16 @@ 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) + .align 32 +SYM_CODE_START(__x86_indirect_thunk_array) + #define GEN(reg) THUNK reg #include <asm/GEN-for-each-reg.h> #undef GEN + .align 32 +SYM_CODE_END(__x86_indirect_thunk_array) + #define GEN(reg) EXPORT_THUNK(reg) #include <asm/GEN-for-each-reg.h> #undef GEN
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