lkml.org 
[lkml]   [2018]   [Nov]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [RFC PATCH 1/3] static_call: Add static call infrastructure
On 9 November 2018 at 16:14, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> On 9 November 2018 at 16:10, Josh Poimboeuf <jpoimboe@redhat.com> 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.

\
 
 \ /
  Last update: 2018-11-09 18:27    [W:0.080 / U:13.588 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site