This is a note to let you know that I've just added the patch titled virtio-console: avoid DMA from stack to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: virtio-console-avoid-dma-from-stack.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From c4baad50297d84bde1a7ad45e50c73adae4a2192 Mon Sep 17 00:00:00 2001 From: Omar Sandoval <osandov@xxxxxx> Date: Wed, 1 Feb 2017 00:02:27 -0800 Subject: virtio-console: avoid DMA from stack From: Omar Sandoval <osandov@xxxxxx> commit c4baad50297d84bde1a7ad45e50c73adae4a2192 upstream. put_chars() stuffs the buffer it gets into an sg, but that buffer may be on the stack. This breaks with CONFIG_VMAP_STACK=y (for me, it manifested as printks getting turned into NUL bytes). Signed-off-by: Omar Sandoval <osandov@xxxxxx> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> Reviewed-by: Amit Shah <amit.shah@xxxxxxxxxx> Cc: Ben Hutchings <ben@xxxxxxxxxxxxxxx> Cc: Brad Spengler <spender@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/char/virtio_console.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) --- a/drivers/char/virtio_console.c +++ b/drivers/char/virtio_console.c @@ -1136,6 +1136,8 @@ static int put_chars(u32 vtermno, const { struct port *port; struct scatterlist sg[1]; + void *data; + int ret; if (unlikely(early_put_chars)) return early_put_chars(vtermno, buf, count); @@ -1144,8 +1146,14 @@ static int put_chars(u32 vtermno, const if (!port) return -EPIPE; - sg_init_one(sg, buf, count); - return __send_to_port(port, sg, 1, count, (void *)buf, false); + data = kmemdup(buf, count, GFP_ATOMIC); + if (!data) + return -ENOMEM; + + sg_init_one(sg, data, count); + ret = __send_to_port(port, sg, 1, count, data, false); + kfree(data); + return ret; } /* Patches currently in stable-queue which might be from osandov@xxxxxx are queue-4.9/x86-efi-don-t-try-to-reserve-runtime-regions.patch queue-4.9/virtio-console-avoid-dma-from-stack.patch