There are 2 mm_init functions in kernel.
One in kernel/fork.c:
static struct mm_struct *mm_init(struct mm_struct *mm,
struct task_struct *p,
struct user_namespace *user_ns)
And another one in init/main.c:
static void __init mm_init(void)
The BTF data will get the first one, which is most likely
(in my case) mm_init from init/main.c without arguments.
Then in runtime when we want to attach to 'mm_init' the
kalsyms contains address of the one from kernel/fork.c.
So we have function model with no arguments and using it
to attach function with 3 arguments.. as result the trampoline
will not save function's arguments and we get crash because
trampoline changes argument registers:
BUG: unable to handle page fault for address: 0000607d87a1d558
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 0 P4D 0
Oops: 0002 [#1] SMP PTI
CPU: 6 PID: 936 Comm: systemd Not tainted 5.12.0-rc4qemu+ #191
RIP: 0010:mm_init+0x223/0x2a0
...
Call Trace:
? bpf_trampoline_6442453476_0+0x3b/0x1000
dup_mm+0x66/0x5f0
? __lock_task_sighand+0x3a/0x70
copy_process+0x17d0/0x1b50
kernel_clone+0x97/0x3c0
__do_sys_clone+0x60/0x80
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f1dc9b3201f
I think there might be more cases like this, but I don't have
an idea yet how to solve this in generic way. The rename in
this change fix it for this instance.
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
init/main.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/init/main.c b/init/main.c
index 53b278845b88..bc1bfe57daf7 100644
--- a/init/main.c
+++ b/init/main.c
@@ -818,7 +818,7 @@ static void __init report_meminit(void)
/*
* Set up kernel memory allocators
*/
-static void __init mm_init(void)
+static void __init init_mem(void)
{
/*
* page_ext requires contiguous pages,
@@ -905,7 +905,7 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
vfs_caches_init_early();
sort_main_extable();
trap_init();
- mm_init();
+ init_mem();
ftrace_init();
--
2.30.2
