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SubjectRe: [RFC PATCH 6/8] preempt/dynamic: Provide preempt_schedule[_notrace]() static calls
On Wed, Jan 27, 2021 at 05:18:37PM -0600, Josh Poimboeuf wrote:

> +static struct static_call_tramp_key *tramp_key_lookup(unsigned long addr)
> +{
> + struct static_call_tramp_key *start = __start_static_call_tramp_key;
> + struct static_call_tramp_key *stop = __stop_static_call_tramp_key;
> + struct static_call_tramp_key *tramp_key;
> +
> + for (tramp_key = start; tramp_key != stop; tramp_key++) {
> + unsigned long tramp;
> +
> + tramp = (long)tramp_key->tramp + (long)&tramp_key->tramp;
> + if (tramp == addr)
> + return tramp_key;
> + }
> +
> + return NULL;
> +}
> +
> static int static_call_add_module(struct module *mod)
> {
> - return __static_call_init(mod, mod->static_call_sites,
> - mod->static_call_sites + mod->num_static_call_sites);
> + struct static_call_site *start = mod->static_call_sites;
> + struct static_call_site *stop = start + mod->num_static_call_sites;
> + struct static_call_site *site;
> +
> + for (site = start; site != stop; site++) {
> + unsigned long addr = (unsigned long)static_call_key(site);
> + struct static_call_tramp_key *tramp_key;
> +
> + /*
> + * Is the key is exported, 'addr' points to the key, which
> + * means modules are allowed to call static_call_update() on
> + * it.
> + *
> + * Otherwise, the key isn't exported, and 'addr' points to the
> + * trampoline so we need to lookup the key.
> + *
> + * We go through this dance to prevent crazy modules from
> + * abusing sensitive static calls.
> + */
> + if (!kernel_text_address(addr))
> + continue;
> +
> + tramp_key = tramp_key_lookup(addr);
> + if (!tramp_key) {
> + pr_warn("Failed to fixup __raw_static_call() usage at: %ps\n",
> + static_call_addr(site));
> + return -EINVAL;
> + }
> +
> + site->key = ((long)tramp_key->key - (long)&tramp_key->key) |
> + (site->key & STATIC_CALL_SITE_FLAGS);
> + }
> +
> + return __static_call_init(mod, start, stop);
> }

I find it works better with this on..

---
diff --git a/kernel/static_call.c b/kernel/static_call.c
index 5e6f567976c1..6906c6ec4c97 100644
--- a/kernel/static_call.c
+++ b/kernel/static_call.c
@@ -325,7 +325,7 @@ static int __static_call_mod_text_reserved(void *start, void *end)
return ret;
}

-static struct static_call_tramp_key *tramp_key_lookup(unsigned long addr)
+static unsigned long tramp_key_lookup(unsigned long addr)
{
struct static_call_tramp_key *start = __start_static_call_tramp_key;
struct static_call_tramp_key *stop = __stop_static_call_tramp_key;
@@ -336,10 +336,10 @@ static struct static_call_tramp_key *tramp_key_lookup(unsigned long addr)

tramp = (long)tramp_key->tramp + (long)&tramp_key->tramp;
if (tramp == addr)
- return tramp_key;
+ return (long)tramp_key->key + (long)&tramp_key->key;
}

- return NULL;
+ return 0;
}

static int static_call_add_module(struct module *mod)
@@ -350,7 +350,7 @@ static int static_call_add_module(struct module *mod)

for (site = start; site != stop; site++) {
unsigned long addr = (unsigned long)static_call_key(site);
- struct static_call_tramp_key *tramp_key;
+ unsigned long key;

/*
* Is the key is exported, 'addr' points to the key, which
@@ -366,14 +366,14 @@ static int static_call_add_module(struct module *mod)
if (!kernel_text_address(addr))
continue;

- tramp_key = tramp_key_lookup(addr);
- if (!tramp_key) {
+ key = tramp_key_lookup(addr);
+ if (!key) {
pr_warn("Failed to fixup __raw_static_call() usage at: %ps\n",
static_call_addr(site));
return -EINVAL;
}

- site->key = ((long)tramp_key->key - (long)&tramp_key->key) |
+ site->key = (key - (long)&site->key) |
(site->key & STATIC_CALL_SITE_FLAGS);
}

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