On Fri, Apr 30, 2021 at 6:48 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> 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.
Just retroactively renaming functions and waiting for someone else to
report similar issues is probably not the best strategy. Should
resolve_btfids detect all name duplicates and emit warnings for them?
It would be good to also remove such name-conflicting FUNCs from BTF
(though currently it's not easy). And fail if such a function is
referenced from .BTF_ids section.
Thoughts?
>
> 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();
nit: given trap_init and ftrace_init, mem_init probably would be a better name?
>
> ftrace_init();
>
> --
> 2.30.2
>
