4.4-stable review patch. If anyone has any objections, please let me know.
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From: Gustavo A. R. Silva gustavo@embeddedor.com
commit e97267cb4d1ee01ca0929638ec0fcbb0904f903d upstream.
vsa.console is indirectly controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability.
This issue was detected with the help of Smatch:
drivers/tty/vt/vt_ioctl.c:711 vt_ioctl() warn: potential spectre issue 'vc_cons' [r]
Fix this by sanitizing vsa.console before using it to index vc_cons
Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1].
[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
Cc: stable@vger.kernel.org Signed-off-by: Gustavo A. R. Silva gustavo@embeddedor.com Reviewed-by: Alan Cox alan@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/tty/vt/vt_ioctl.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/drivers/tty/vt/vt_ioctl.c +++ b/drivers/tty/vt/vt_ioctl.c @@ -31,6 +31,8 @@ #include <asm/io.h> #include <asm/uaccess.h>
+#include <linux/nospec.h> + #include <linux/kbd_kern.h> #include <linux/vt_kern.h> #include <linux/kbd_diacr.h> @@ -703,6 +705,8 @@ int vt_ioctl(struct tty_struct *tty, if (vsa.console == 0 || vsa.console > MAX_NR_CONSOLES) ret = -ENXIO; else { + vsa.console = array_index_nospec(vsa.console, + MAX_NR_CONSOLES + 1); vsa.console--; console_lock(); ret = vc_allocate(vsa.console);