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charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B8FE3C0016 X-Stat-Signature: 9pcybbpgyw9mszzpmm1k9k5ybbemamdn X-Rspam-User: X-HE-Tag: 1713174738-913247 X-HE-Meta: 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 tqDVZcRa dlWxzfcmHTNQ4TrN1bxkvl1N75UeknY1NapOUPb0xbCse0mqEw9d1cX+CtYKwjvIl2LDYUKekerDX7sbCbSatLobjDRpFkwUZbpNzEOCwThTeJKU9fbpbLHH5lFTLMJPzns3Ga0JRv31XF7V3L5Vbgdx2w+tcF19GSBJNLQ410SGMEU0wM93qthxszSpvBbDfgqvto0rMmqyQzIq24xhOs+HSyJG9vNbdbe2qJje8r994U1CQQ/Gpjdc4jN2/Wtin7CWIrAGKmhvudmN3IkM8w9pwS3AcMM1Yz6K5yhH68c1fEFW5TxO6ASyzrji+HUVRiAdT X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 15.04.24 11:44, Alice Ryhl wrote: > On Mon, Apr 15, 2024 at 11:37=E2=80=AFAM Benno Lossin wrote: >> >> On 15.04.24 09:13, Alice Ryhl wrote: >>> +impl UserSlice { >>> + /// Constructs a user slice from a raw pointer and a length in byt= es. >>> + /// >>> + /// Constructing a [`UserSlice`] performs no checks on the provide= d address and length, it can >>> + /// safely be constructed inside a kernel thread with no current u= serspace process. Reads and >>> + /// writes wrap the kernel APIs `copy_from_user` and `copy_to_user= `, which check the memory map >>> + /// of the current process and enforce that the address range is w= ithin the user range (no >>> + /// additional calls to `access_ok` are needed). >>> + /// >>> + /// Callers must be careful to avoid time-of-check-time-of-use (TO= CTOU) issues. The simplest way >>> + /// is to create a single instance of [`UserSlice`] per user memor= y block as it reads each byte >>> + /// at most once. >>> + pub fn new(ptr: *mut c_void, length: usize) -> Self { >> >> What would happen if I call this with a kernel pointer and then >> read/write to it? For example >> >> let mut arr =3D [MaybeUninit::uninit(); 64]; >> let ptr: *mut [MaybeUninit] =3D &mut arr; >> let ptr =3D ptr.cast::(); >> >> let slice =3D UserSlice::new(ptr, 64); >> let (mut r, mut w) =3D slice.reader_writer(); >> >> r.read_raw(&mut arr)?; >> // SAFETY: `arr` was initialized above. >> w.write_slice(unsafe { MaybeUninit::slice_assume_init_ref(&arr) })= ?; >> >> I think this would violate the exclusivity of `&mut` without any >> `unsafe` code. (the `unsafe` block at the end cannot possibly be wrong) >=20 > This will fail with an EFAULT error. There is a check on the C side > that verifies that the address is in userspace. (The access_ok call.) I see, that makes a lot of sense. Regardless of whether you fix the nit about the guarantees section: Reviewed-by: Benno Lossin --=20 Cheers, Benno