On Fri, Nov 09, 2018 at 02:39:17PM +0100, Ard Biesheuvel wrote: > > + for (site = start; site < stop; site++) { > > + struct static_call_key *key = static_call_key(site); > > + unsigned long addr = static_call_addr(site); > > + > > + if (list_empty(&key->site_mods)) { > > + struct static_call_mod *mod; > > + > > + mod = kzalloc(sizeof(*mod), GFP_KERNEL); > > + if (!mod) { > > + WARN(1, "Failed to allocate memory for > > static calls"); > > + return; > > + } > > + > > + mod->sites = site; > > + list_add_tail(&mod->list, &key->site_mods); > > + > > + /* > > + * The trampoline should no longer be used. Poison > > it > > + * it with a BUG() to catch any stray callers. > > + */ > > + arch_static_call_poison_tramp(addr); > > This patches the wrong thing: the trampoline is at key->func not addr.
If you look at the x86 implementation, it actually does poison the trampoline. The address of the trampoline isn't actually known here. key->func isn't the trampoline address; it's the destination func address. So instead I passed the address of the call instruction. The arch code then reads the instruction to find the callee (the trampoline). The code is a bit confusing. To make it more obvious, maybe we should add another arch function to read the call destination. Then this code can pass that into arch_static_call_poison_tramp(). > However, patching it here means we poison it before all users are > patched. I added this on top > > diff --git a/kernel/static_call.c b/kernel/static_call.c > index 599ebc6fc4f1..d9562329bec6 100644 > --- a/kernel/static_call.c > +++ b/kernel/static_call.c > @@ -248,6 +248,7 @@ static void __init static_call_init(void) > struct static_call_site *start = __start_static_call_sites; > struct static_call_site *stop = __stop_static_call_sites; > struct static_call_site *site; > + struct static_call_key *prev_key = NULL; > > if (start == stop) { > pr_warn("WARNING: empty static call table\n"); > @@ -279,7 +280,9 @@ static void __init static_call_init(void) > * The trampoline should no longer be used. Poison it > * it with a BUG() to catch any stray callers. > */ > - arch_static_call_poison_tramp(addr); > + if (prev_key) > + > arch_static_call_poison_tramp((unsigned long)prev_key->func); > + prev_key = key; > } > > arch_static_call_transform(addr, key->func); While it does indeed poison the trampoline before all users are patched, I had been thinking that it didn't really matter because this is before the other CPUs have been booted. But I believe interrupts are enabled at this point during the boot, so it would indeed be wise to poison it afterwards, in case an irq handler makes a static call. -- Josh