On 9 November 2018 at 16:14, Ard Biesheuvel <[email protected]> wrote: > On 9 November 2018 at 16:10, Josh Poimboeuf <[email protected]> wrote: >> 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(). >> > > Ah right, so I am basically missing a dereference in my > arch_static_call_poison_tramp() code if this breaks. >
Could we call it 'defuse' rather than 'poision'? On arm64, we will need to keep it around to bounce function calls that are out of range, and replace it with a PLT sequence.
