From 0c75fee1bc3154c21078c61787a52058aae984e2 Mon Sep 17 00:00:00 2001 From: Keir Fraser Date: Tue, 14 Apr 2009 11:21:45 +0100 Subject: minios: fix a memory corruption in blkfront The corruption happens every time we pass a sector aligned buffer (instead of a page aligned buffer) to blkfront_aio. To trigger the COW we have to write at least a byte to each page of the buffer, but we must be careful not to overwrite useful content. Signed-off-by: Stefano Stabellini --- extras/mini-os/blkfront.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) (limited to 'extras/mini-os/blkfront.c') diff --git a/extras/mini-os/blkfront.c b/extras/mini-os/blkfront.c index d4b0ea54ce..75add45fb4 100644 --- a/extras/mini-os/blkfront.c +++ b/extras/mini-os/blkfront.c @@ -316,20 +316,22 @@ void blkfront_aio(struct blkfront_aiocb *aiocbp, int write) req->id = (uintptr_t) aiocbp; req->sector_number = aiocbp->aio_offset / dev->info.sector_size; + for (j = 0; j < n; j++) { + req->seg[j].first_sect = 0; + req->seg[j].last_sect = PAGE_SIZE / dev->info.sector_size - 1; + } + req->seg[0].first_sect = ((uintptr_t)aiocbp->aio_buf & ~PAGE_MASK) / dev->info.sector_size; + req->seg[n-1].last_sect = (((uintptr_t)aiocbp->aio_buf + aiocbp->aio_nbytes - 1) & ~PAGE_MASK) / dev->info.sector_size; for (j = 0; j < n; j++) { uintptr_t data = start + j * PAGE_SIZE; if (!write) { /* Trigger CoW if needed */ - *(char*)data = 0; + *(char*)(data + (req->seg[j].first_sect << 9)) = 0; barrier(); } aiocbp->gref[j] = req->seg[j].gref = gnttab_grant_access(dev->dom, virtual_to_mfn(data), write); - req->seg[j].first_sect = 0; - req->seg[j].last_sect = PAGE_SIZE / dev->info.sector_size - 1; } - req->seg[0].first_sect = ((uintptr_t)aiocbp->aio_buf & ~PAGE_MASK) / dev->info.sector_size; - req->seg[n-1].last_sect = (((uintptr_t)aiocbp->aio_buf + aiocbp->aio_nbytes - 1) & ~PAGE_MASK) / dev->info.sector_size; dev->ring.req_prod_pvt = i + 1; -- cgit v1.2.3