Re: [PATCH] pktcdvd: Fix possible Spectre-v1 for pkt_devs
From: Gustavo A. R. Silva <hidden>
Date: 2018-07-28 01:48:17
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Hi Jinbum, Thanks for working on this. Please, see some comments below. On 07/27/2018 08:31 PM, Jinbum Park wrote:
quoted hunk ↗ jump to hunk
User controls @dev_minor which to be used as index of pkt_devs. So, It can be exploited via Spectre-like attack. (speculative execution) This kind of attack leaks address of pkt_devs, [1] It leads an attacker to bypass security mechanism such as KASLR. So sanitize @dev_minor before using it to prevent attack. [1] https://github.com/jinb-park/linux-exploit/ tree/master/exploit-remaining-spectre-gadget/leak_pkt_devs.c Signed-off-by: Jinbum Park <redacted> --- drivers/block/pktcdvd.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c index c61d20c..665760d 100644 --- a/drivers/block/pktcdvd.c +++ b/drivers/block/pktcdvd.c@@ -67,8 +67,8 @@ #include <scsi/scsi.h> #include <linux/debugfs.h> #include <linux/device.h> - #include <linux/uaccess.h> +#include <linux/nospec.h> #define DRIVER_NAME "pktcdvd"@@ -2229,9 +2229,13 @@ static void pkt_release_dev(struct pktcdvd_device *pd, int flush) static struct pktcdvd_device *pkt_find_dev_from_minor(unsigned int dev_minor) { + unsigned int idx = 0; +
There is no need for a new variable in this case.
if (dev_minor >= MAX_WRITERS) return NULL; - return pkt_devs[dev_minor]; + + idx = array_index_nospec(dev_minor, MAX_WRITERS); + return pkt_devs[idx];
Also, the following style is preferred: if (dev_minor >= MAX_WRITERS) return NULL; dev_minor = array_index_nospec(dev_minor, MAX_WRITERS); Thanks -- Gustavo