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io_uring/kbuf: disallow mapping a badly aligned provided ring buffer

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On at least parisc, we have strict requirements on how we virtually map
an address that is shared between the application and the kernel. On
these platforms, IOU_PBUF_RING_MMAP should be used when setting up a
shared ring buffer for provided buffers. If the application is mapping
these pages and asking the kernel to pin+map them as well, then we have
no control over what virtual address we get in the kernel.

For that case, do a sanity check if SHM_COLOUR is defined, and disallow
the mapping request. The application must fall back to using
IOU_PBUF_RING_MMAP for this case, and liburing will do that transparently
with the set of helpers that it has.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2023-03-17 10:42:08 -06:00
parent e1fe7ee885
commit fcb46c0ccc
1 changed files with 18 additions and 0 deletions
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18
io_uring/kbuf.c
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@ -491,6 +491,24 @@ static int io_pin_pbuf_ring(struct io_uring_buf_reg *reg,
return PTR_ERR(pages);
br = page_address(pages[0]);
#ifdef SHM_COLOUR
/*
* On platforms that have specific aliasing requirements, SHM_COLOUR
* is set and we must guarantee that the kernel and user side align
* nicely. We cannot do that if IOU_PBUF_RING_MMAP isn't set and
* the application mmap's the provided ring buffer. Fail the request
* if we, by chance, don't end up with aligned addresses. The app
* should use IOU_PBUF_RING_MMAP instead, and liburing will handle
* this transparently.
*/
if ((reg->ring_addr | (unsigned long) br) & (SHM_COLOUR - 1)) {
int i;
for (i = 0; i < nr_pages; i++)
unpin_user_page(pages[i]);
return -EINVAL;
}
#endif
bl->buf_pages = pages;
bl->buf_nr_pages = nr_pages;
bl->buf_ring = br;