When a module's init text is freed, do_init_module() calls
ftrace_free_mem() with a half-open [start, end) range. However the
ftrace_cmp_recs() comparator treats the upper bound as inclusive, as all
its other users do, passing 'ip + size - 1'. So ftrace_free_mem() can
delete a record sitting exactly at 'end', which is outside the freed
range.
For a kernel without CFI or IBT, the first record of a function is at
the function start, which for the first function in a module is also the
base of its text allocation. As the module allocator packs its regions,
that address is often the 'end' passed by a neighboring module's
do_init_module(), causing the first function's ftrace location to get
disabled, preventing an attempt to livepatch it:
livepatch: failed to find location for function 'pcspkr_probe'
Convert the exclusive end to the inclusive 'end - 1' the comparator
expects, and return early for an empty range to avoid the subtraction
from underflowing when the init text size is zero.
Fixes: 42c269c88dc1 ("ftrace: Allow for function tracing to record init
functions on boot up")
Signed-off-by: Josh Poimboeuf <[email protected]>
---
kernel/trace/ftrace.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f93e34dd23288..6bde28d56f41b 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -8283,7 +8283,8 @@ static void add_to_clear_hash_list(struct list_head
*clear_list,
void ftrace_free_mem(struct module *mod, void *start_ptr, void *end_ptr)
{
unsigned long start = (unsigned long)(start_ptr);
- unsigned long end = (unsigned long)(end_ptr);
+ /* end is inclusive and end_ptr is exclusive */
+ unsigned long end = (unsigned long)(end_ptr) - 1;
struct ftrace_page **last_pg = &ftrace_pages_start;
struct ftrace_page *tmp_page = NULL;
struct ftrace_page *pg;
@@ -8293,6 +8294,9 @@ void ftrace_free_mem(struct module *mod, void *start_ptr,
void *end_ptr)
struct ftrace_init_func *func, *func_next;
LIST_HEAD(clear_hash);
+ if (start_ptr >= end_ptr)
+ return;
+
key.ip = start;
key.flags = end; /* overload flags, as it is unsigned long */
--
2.54.0
