[RFC 12/16] io_uring: convert pointer init to io_region_slice

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

Use io_region_slice() to initialise ctx ring pointers. The helper
performs bound checks and other sanitisation, which is safer and will be
especially helpful when ring placement gets more complicated in coming
patches. It also extends struct io_scq_dim with all intermediate offsets
and sizes to fully describe rings.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/io_uring.c | 47 ++++++++++++++++++++++++---------------------
 io_uring/io_uring.h |  2 ++
 2 files changed, 27 insertions(+), 22 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 9aef41f6ce23..4f38a0b587fd 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -2759,9 +2759,7 @@ static void io_rings_free(struct io_ring_ctx *ctx)
 int rings_size(unsigned int flags, unsigned int sq_entries,
 	       unsigned int cq_entries, struct io_scq_dim *dims)
 {
-	size_t off, sq_array_size;
-	size_t cq_size, cqe_size;
-	size_t sqe_size;
+	size_t cqe_size, off, sqe_size;
 
 	dims->sq_array_offset = SIZE_MAX;
 
@@ -2773,18 +2771,18 @@ int rings_size(unsigned int flags, unsigned int sq_entries,
 		cqe_size *= 2;
 
 	dims->sq_size = array_size(sqe_size, sq_entries);
-	if (dims->sq_size == SIZE_MAX)
+	dims->sq_array_size = array_size(sizeof(u32), sq_entries);
+	dims->cq_size = array_size(cqe_size, cq_entries);
+
+	if (dims->sq_size == SIZE_MAX || dims->cq_size == SIZE_MAX ||
+	    dims->sq_array_size == SIZE_MAX)
 		return -EOVERFLOW;
 
 	off = sizeof(struct io_rings);
 	off = L1_CACHE_ALIGN(off);
 	dims->cq_offset = off;
 
-	cq_size = array_size(cqe_size, cq_entries);
-	if (cq_size == SIZE_MAX)
-		return -EOVERFLOW;
-
-	off = size_add(off, cq_size);
+	off = size_add(off, dims->cq_size);
 	if (off == SIZE_MAX)
 		return -EOVERFLOW;
 
@@ -2809,12 +2807,7 @@ int rings_size(unsigned int flags, unsigned int sq_entries,
 	}
 
 	dims->sq_array_offset = off;
-
-	sq_array_size = array_size(sizeof(u32), sq_entries);
-	if (sq_array_size == SIZE_MAX)
-		return -EOVERFLOW;
-
-	if (check_add_overflow(off, sq_array_size, &off))
+	if (check_add_overflow(off, dims->sq_array_size, &off))
 		return -EOVERFLOW;
 
 	dims->cq_comp_size = off;
@@ -3375,7 +3368,6 @@ static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx,
 	struct io_scq_dim *dims = &config->dims;
 	struct io_uring_region_desc rd;
 	struct io_rings *rings;
-	void *ptr;
 	int ret;
 
 	/* make sure these are sane, as we already accounted them */
@@ -3391,12 +3383,19 @@ static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx,
 	ret = io_create_region(ctx, &ctx->ring_region, &rd, IORING_OFF_CQ_RING);
 	if (ret)
 		return ret;
-	ptr = io_region_get_ptr(&ctx->ring_region);
-	ctx->rings = rings = ptr;
-	ctx->cqes = ptr + config->dims.cq_offset;
 
-	if (!(ctx->flags & IORING_SETUP_NO_SQARRAY))
-		ctx->sq_array = ptr + dims->sq_array_offset;
+	ctx->rings = io_region_slice(&ctx->ring_region, 0, sizeof(struct io_rings));
+	ctx->cqes = io_region_slice(&ctx->ring_region, dims->cq_offset, dims->cq_size);
+	if (!ctx->rings || !ctx->cqes)
+		return -EFAULT;
+
+	if (!(ctx->flags & IORING_SETUP_NO_SQARRAY)) {
+		ctx->sq_array = io_region_slice(&ctx->ring_region,
+						dims->sq_array_offset,
+						dims->sq_array_size);
+		if (!ctx->sq_array)
+			return -EFAULT;
+	}
 
 	memset(&rd, 0, sizeof(rd));
 	rd.size = PAGE_ALIGN(dims->sq_size);
@@ -3409,8 +3408,12 @@ static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx,
 		io_rings_free(ctx);
 		return ret;
 	}
-	ctx->sq_sqes = io_region_get_ptr(&ctx->sq_region);
 
+	ctx->sq_sqes = io_region_slice(&ctx->sq_region, 0, dims->sq_size);
+	if (!ctx->sq_sqes)
+		return -EFAULT;
+
+	rings = ctx->rings;
 	memset(rings, 0, sizeof(*rings));
 	WRITE_ONCE(rings->sq_ring_mask, ctx->sq_entries - 1);
 	WRITE_ONCE(rings->cq_ring_mask, ctx->cq_entries - 1);
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 80228c5a843c..ed57ab4161db 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -19,8 +19,10 @@
 
 struct io_scq_dim {
 	size_t sq_array_offset;
+	size_t sq_array_size;
 	size_t sq_size;
 	size_t cq_offset;
+	size_t cq_size;
 
 	/* Compound array mmap'ed together with CQ. */
 	size_t cq_comp_size;
-- 
2.49.0