On Thu, 13 Apr 2023 12:13:36 +0800 Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
> The dump_user_range() is used to copy the user page to a coredump
> file, but if a hardware memory error occurred during copy, which
> called from __kernel_write_iter() in dump_user_range(), it crashs,
>
> CPU: 112 PID: 7014 Comm: mca-recover Not tainted 6.3.0-rc2 #425
>
> pc : __memcpy+0x110/0x260
> lr : _copy_from_iter+0x3bc/0x4c8
> ...
> Call trace:
> __memcpy+0x110/0x260
> copy_page_from_iter+0xcc/0x130
> pipe_write+0x164/0x6d8
> __kernel_write_iter+0x9c/0x210
> dump_user_range+0xc8/0x1d8
> elf_core_dump+0x308/0x368
> do_coredump+0x2e8/0xa40
> get_signal+0x59c/0x788
> do_signal+0x118/0x1f8
> do_notify_resume+0xf0/0x280
> el0_da+0x130/0x138
> el0t_64_sync_handler+0x68/0xc0
> el0t_64_sync+0x188/0x190
>
> Generally, the '->write_iter' of file ops will use copy_page_from_iter()
> and copy_page_from_iter_atomic(), change memcpy() to copy_mc_to_kernel()
> in both of them to handle #MC during source read, which stop coredump
> processing and kill the task instead of kernel panic, but the source
> address may not always an user address, so introduce a new copy_mc flag
> in struct iov_iter{} to indicate that the iter could do a safe memory
> copy, also introduce the helpers to set/clear/check the flag, for now,
> it's only used in coredump's dump_user_range(), but it could expand to
> any other scenarios to fix the similar issue.
>
> ...
>
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -291,6 +291,7 @@ void iov_iter_init(struct iov_iter *i, unsigned int direction,
> .nofault = false,
> .user_backed = true,
> .data_source = direction,
> + .copy_mc = false,
> .__iov = iov,
> .nr_segs = nr_segs,
> .iov_offset = 0,
hm, linux-next. mm.git doesn't have the other iov_iter changes, so I
repositioned the iov_iter.copy_mc field so the patch should fuzzily
apply to kernels with or without de4f5fed3f231a8 ("iov_iter: add
iter_iovec() helper"),
