From fcb46c0ccc7c07af54f818fd498e461353ea50e7 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 17 Mar 2023 10:42:08 -0600 Subject: [PATCH] io_uring/kbuf: disallow mapping a badly aligned provided ring buffer 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 --- io_uring/kbuf.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c index cd1d9dddf58e..79c25459e8de 100644 --- a/io_uring/kbuf.c +++ b/io_uring/kbuf.c @@ -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;