Messages in this thread | | | Date | Mon, 26 Nov 2018 17:02:17 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64 |
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On Mon, Nov 26, 2018 at 07:55:00AM -0600, Josh Poimboeuf wrote: > diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c > index 8026d176f25c..d3869295b88d 100644 > --- a/arch/x86/kernel/static_call.c > +++ b/arch/x86/kernel/static_call.c > @@ -9,13 +9,21 @@ > > void static_call_bp_handler(void); > void *bp_handler_dest; > +void *bp_handler_continue; > > asm(".pushsection .text, \"ax\" \n" > ".globl static_call_bp_handler \n" > ".type static_call_bp_handler, @function \n" > "static_call_bp_handler: \n" > - "ANNOTATE_RETPOLINE_SAFE \n" > +#ifdef CONFIG_HAVE_STATIC_CALL_INLINE > + ANNOTATE_RETPOLINE_SAFE > + "call *bp_handler_dest \n" > + ANNOTATE_RETPOLINE_SAFE > + "jmp *bp_handler_continue \n" > +#else /* !CONFIG_HAVE_STATIC_CALL_INLINE */ > + ANNOTATE_RETPOLINE_SAFE > "jmp *bp_handler_dest \n" > +#endif > ".popsection \n"); > > void arch_static_call_transform(void *site, void *tramp, void *func) > @@ -25,7 +33,10 @@ void arch_static_call_transform(void *site, void *tramp, void *func) > unsigned char insn_opcode; > unsigned char opcodes[CALL_INSN_SIZE]; > > - insn = (unsigned long)tramp; > + if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE)) > + insn = (unsigned long)site; > + else > + insn = (unsigned long)tramp; > > mutex_lock(&text_mutex); > > @@ -41,8 +52,10 @@ void arch_static_call_transform(void *site, void *tramp, void *func) > opcodes[0] = insn_opcode; > memcpy(&opcodes[1], &dest_relative, CALL_INSN_SIZE - 1); > > - /* Set up the variable for the breakpoint handler: */ > + /* Set up the variables for the breakpoint handler: */ > bp_handler_dest = func; > + if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE)) > + bp_handler_continue = (void *)(insn + CALL_INSN_SIZE); > > /* Patch the call site: */ > text_poke_bp((void *)insn, opcodes, CALL_INSN_SIZE,
OK, so this is where that static_call_bp_handler comes from; you need that CALL to frob the stack.
But I still think it is broken; consider:
CPU0 CPU1
bp_handler = ponies;
text_poke_bp(, &static_call_bp_handler) text_poke(&int3); on_each_cpu(sync) <IPI> ... </IPI>
text_poke(/* all but first bytes */) on_each_cpu(sync) <IPI> ... </IPI>
<int3> pt_regs->ip = &static_call_bp_handler </int3>
// VCPU takes a nap... text_poke(/* first byte */) on_each_cpu(sync) <IPI> ... </IPI>
// VCPU sleeps more bp_handler = unicorn;
CALL unicorn
*whoops*
Now, granted, that is all rather 'unlikely', but that never stopped Murphy.
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