On Mon, Nov 26, 2018 at 10:28:08AM -0800, Andy Lutomirski wrote: > On Mon, Nov 26, 2018 at 9:10 AM Josh Poimboeuf <[email protected]> wrote: > > > > On Mon, Nov 26, 2018 at 05:02:17PM +0100, Peter Zijlstra wrote: > > > 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. > > > > Good find, thanks Peter. > > > > As we discussed on IRC, we'll need to fix this from within the int3 > > exception handler by faking the call: putting a fake return address on > > the stack (pointing to right after the call) and setting regs->ip to the > > called function. > > Can you add a comment that it will need updating when kernel CET is added?
Will do, though I get the feeling there's a lot of other (existing) code that will also need to change for kernel CET. -- Josh
