static_call: Fix the module key fixup

Provided the target address of a R_X86_64_PC32 relocation is aligned,
the low two bits should be invariant between the relative and absolute
value.

Turns out the address is not aligned and things go sideways, ensure we
transfer the bits in the absolute form when fixing up the key address.

Fixes: 73f44fe19d35 ("static_call: Allow module use without exposing static_call_key")
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lkml.kernel.org/r/20210225220351.GE4746@worktop.programming.kicks-ass.net

diff --git a/kernel/static_call.c b/kernel/static_call.c
index 6906c6ec4c97d99772f286fa58836c2119896b97..ae825295cf685f387fe60ce45445dd7f7c4f1a4b 100644 (file)
--- a/kernel/static_call.c
+++ b/kernel/static_call.c
@@ -349,7 +349,8 @@ static int static_call_add_module(struct module *mod)
        struct static_call_site *site;
 
        for (site = start; site != stop; site++) {
-               unsigned long addr = (unsigned long)static_call_key(site);
+               unsigned long s_key = (long)site->key + (long)&site->key;
+               unsigned long addr = s_key & ~STATIC_CALL_SITE_FLAGS;
                unsigned long key;
 
                /*
@@ -373,8 +374,8 @@ static int static_call_add_module(struct module *mod)
                        return -EINVAL;
                }
 
-               site->key = (key - (long)&site->key) |
-                           (site->key & STATIC_CALL_SITE_FLAGS);
+               key |= s_key & STATIC_CALL_SITE_FLAGS;
+               site->key = key - (long)&site->key;
        }
 
        return __static_call_init(mod, start, stop);