Re: [PATCH] io_uring: annotate the struct io_kiocb slab for appropriate user copy

[Pavel Begunkov <asml.silence@gmail.com>]

On 8/2/23 21:42, Jens Axboe wrote:
> When compiling the kernel with clang and having HARDENED_USERCOPY
> enabled, the liburing openat2.t test case fails during request setup:
> 
> usercopy: Kernel memory overwrite attempt detected to SLUB object 'io_kiocb' (offset 24, size 24)!
> ------------[ cut here ]------------
> kernel BUG at mm/usercopy.c:102!
> invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> CPU: 3 PID: 413 Comm: openat2.t Tainted: G                 N 6.4.3-g6995e2de6891-dirty #19
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.1-0-g3208b098f51a-prebuilt.qemu.org 04/01/2014
> RIP: 0010:usercopy_abort+0x84/0x90
> Code: ce 49 89 ce 48 c7 c3 68 48 98 82 48 0f 44 de 48 c7 c7 56 c6 94 82 4c 89 de 48 89 c1 41 52 41 56 53 e8 e0 51 c5 00 48 83 c4 18 <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 41 57 41 56
> RSP: 0018:ffffc900016b3da0 EFLAGS: 00010296
> RAX: 0000000000000062 RBX: ffffffff82984868 RCX: 4e9b661ac6275b00
> RDX: ffff8881b90ec580 RSI: ffffffff82949a64 RDI: 00000000ffffffff
> RBP: 0000000000000018 R08: 0000000000000000 R09: 0000000000000000
> R10: ffffc900016b3c88 R11: ffffc900016b3c30 R12: 00007ffe549659e0
> R13: ffff888119014000 R14: 0000000000000018 R15: 0000000000000018
> FS:  00007f862e3ca680(0000) GS:ffff8881b90c0000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005571483542a8 CR3: 0000000118c11000 CR4: 00000000003506e0
> Call Trace:
>   <TASK>
>   ? __die_body+0x63/0xb0
>   ? die+0x9d/0xc0
>   ? do_trap+0xa7/0x180
>   ? usercopy_abort+0x84/0x90
>   ? do_error_trap+0xc6/0x110
>   ? usercopy_abort+0x84/0x90
>   ? handle_invalid_op+0x2c/0x40
>   ? usercopy_abort+0x84/0x90
>   ? exc_invalid_op+0x2f/0x40
>   ? asm_exc_invalid_op+0x16/0x20
>   ? usercopy_abort+0x84/0x90
>   __check_heap_object+0xe2/0x110
>   __check_object_size+0x142/0x3d0
>   io_openat2_prep+0x68/0x140
>   io_submit_sqes+0x28a/0x680
>   __se_sys_io_uring_enter+0x120/0x580
>   do_syscall_64+0x3d/0x80
>   entry_SYSCALL_64_after_hwframe+0x46/0xb0
> RIP: 0033:0x55714834de26
> Code: ca 01 0f b6 82 d0 00 00 00 8b ba cc 00 00 00 45 31 c0 31 d2 41 b9 08 00 00 00 83 e0 01 c1 e0 04 41 09 c2 b8 aa 01 00 00 0f 05 <c3> 66 0f 1f 84 00 00 00 00 00 89 30 eb 89 0f 1f 40 00 8b 00 a8 06
> RSP: 002b:00007ffe549659c8 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
> RAX: ffffffffffffffda RBX: 00007ffe54965a50 RCX: 000055714834de26
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000003
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000008
> R10: 0000000000000000 R11: 0000000000000246 R12: 000055714834f057
> R13: 00007ffe54965a50 R14: 0000000000000001 R15: 0000557148351dd8
>   </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:usercopy_abort+0x84/0x90
> Code: ce 49 89 ce 48 c7 c3 68 48 98 82 48 0f 44 de 48 c7 c7 56 c6 94 82 4c 89 de 48 89 c1 41 52 41 56 53 e8 e0 51 c5 00 48 83 c4 18 <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 41 57 41 56
> RSP: 0018:ffffc900016b3da0 EFLAGS: 00010296
> RAX: 0000000000000062 RBX: ffffffff82984868 RCX: 4e9b661ac6275b00
> RDX: ffff8881b90ec580 RSI: ffffffff82949a64 RDI: 00000000ffffffff
> RBP: 0000000000000018 R08: 0000000000000000 R09: 0000000000000000
> R10: ffffc900016b3c88 R11: ffffc900016b3c30 R12: 00007ffe549659e0
> R13: ffff888119014000 R14: 0000000000000018 R15: 0000000000000018
> FS:  00007f862e3ca680(0000) GS:ffff8881b90c0000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005571483542a8 CR3: 0000000118c11000 CR4: 00000000003506e0
> Kernel panic - not syncing: Fatal exception
> Kernel Offset: disabled
> ---[ end Kernel panic - not syncing: Fatal exception ]---
> 
> when it tries to copy struct open_how from userspace into the per-command
> space in the io_kiocb. There's nothing wrong with the copy, but we're
> missing the appropriate annotations for allowing user copies to/from the
> io_kiocb slab.
> 
> Allow copies in the per-command area, which is from the 'file' pointer to
> when 'opcode' starts. We do have existing user copies there, but they are
> not all annotated like the one that openat2_prep() uses,
> copy_struct_from_user(). But in practice opcodes should be allowed to
> copy data into their per-command area in the io_kiocb.
> 
> Reported-by: Breno Leitao <leitao@debian.org>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> 
> ---
> 
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 135da2fd0eda..d8e69461786d 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -4627,8 +4627,20 @@ static int __init io_uring_init(void)
>   
>   	io_uring_optable_init();
>   
> -	req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC |
> -				SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
> +	/*
> +	 * Allow user copy in the per-command field, which starts after the
> +	 * file in io_kiocb and until the opcode field. The openat2 handling
> +	 * requires copying in user memory into the io_kiocb object in that
> +	 * range, and HARDENED_USERCOPY will complain if we haven't
> +	 * correctly annotated this range.
> +	 */
> +	req_cachep = kmem_cache_create_usercopy("io_kiocb",
> +				sizeof(struct io_kiocb), 0,
> +				SLAB_HWCACHE_ALIGN | SLAB_PANIC |
> +				SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU,
> +				offsetof(struct io_kiocb, cmd.data),
> +				offsetof(struct io_kiocb, opcode) -
> +				offsetof(struct io_kiocb, cmd.data), NULL);

sizeof_field(struct io_kiocb, cmd.data)

should be less awkward

-- 
Pavel Begunkov