[PATCH 1/1] io_uring: prevent reg-wait speculations

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

With *ENTER_EXT_ARG_REG instead of passing a user pointer with arguments
for the waiting loop the user can specify an offset into a pre-mapped
region of memory, in which case the
[offset, offset + sizeof(io_uring_reg_wait)) will be intepreted as the
argument.

As we address a kernel array using a user given index, it'd be a subject
to speculation type of exploits.

Fixes: d617b3147d54c ("io_uring: restore back registered wait arguments")
Fixes: aa00f67adc2c0 ("io_uring: add support for fixed wait regions")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/io_uring.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index da8fd460977b..3a3e4fca1545 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3207,6 +3207,7 @@ static struct io_uring_reg_wait *io_get_ext_arg_reg(struct io_ring_ctx *ctx,
 		     end > ctx->cq_wait_size))
 		return ERR_PTR(-EFAULT);
 
+	barrier_nospec();
 	return ctx->cq_wait_arg + offset;
 }
 
-- 
2.46.0