Messages in this thread Patches in this message | | | Subject | Re: [PATCH] kernel: sys: fix potential Spectre v1 | From | "Gustavo A. R. Silva" <> | Date | Fri, 18 May 2018 14:04:12 -0500 |
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On 05/15/2018 05:57 PM, Dan Williams wrote: > On Tue, May 15, 2018 at 3:29 PM, Thomas Gleixner <tglx@linutronix.de> wrote: >> On Tue, 15 May 2018, Andrew Morton wrote: >>> On Mon, 14 May 2018 22:00:38 -0500 "Gustavo A. R. Silva" <gustavo@embeddedor.com> wrote: >>> >>>> resource can be 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: >>>> >>>> kernel/sys.c:1474 __do_compat_sys_old_getrlimit() warn: potential >>>> spectre issue 'get_current()->signal->rlim' (local cap) >>>> kernel/sys.c:1455 __do_sys_old_getrlimit() warn: potential spectre issue >>>> 'get_current()->signal->rlim' (local cap) >>>> >>>> Fix this by sanitizing *resource* before using it to index >>>> current->signal->rlim >>>> >>>> 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]. >>> >>> hm. Not my area, but I'm always willing to learn ;) >>> >>>> --- a/kernel/sys.c >>>> +++ b/kernel/sys.c >>>> @@ -69,6 +69,9 @@ >>>> #include <asm/io.h> >>>> #include <asm/unistd.h> >>>> >>>> +/* Hardening for Spectre-v1 */ >>>> +#include <linux/nospec.h> >>>> + >>>> #include "uid16.h" >>>> >>>> #ifndef SET_UNALIGN_CTL >>>> @@ -1451,6 +1454,7 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource, >>>> if (resource >= RLIM_NLIMITS) >>>> return -EINVAL; >>>> >>>> + resource = array_index_nospec(resource, RLIM_NLIMITS); >>>> task_lock(current->group_leader); >>>> x = current->signal->rlim[resource]; >>> >>> Can the speculation proceed past the task_lock()? Or is the policy to >>> ignore such happy happenstances even if they are available? >> >> Locks are not in the way of speculation. Speculation has almost no limits >> except serializing instructions. At least they respect the magic AND >> limitation in array_index_nospec(). > > I'd say it another way, because they don't respect the magic AND, we > just make the result in the speculation path safe. So, it's controlled > speculation. >
Dan,
What do you think about adding the following function to the nospec API:
diff --git a/include/linux/nospec.h b/include/linux/nospec.h index e791ebc..81e9a77 100644 --- a/include/linux/nospec.h +++ b/include/linux/nospec.h @@ -55,4 +55,17 @@ static inline unsigned long array_index_mask_nospec(unsigned long index, \ (typeof(_i)) (_i & _mask); \ }) + + +#ifndef sanitize_index_nospec +inline bool sanitize_index_nospec(unsigned long index, + unsigned long size) +{ + if (index >= size) + return false; + index = array_index_nospec(index, size); + + return true; +} +#endif #endif /* _LINUX_NOSPEC_H */
And here is an example of its use:
diff --git a/drivers/media/i2c/tvp7002.c b/drivers/media/i2c/tvp7002.c index 4599b7e..27b39c0 100644 --- a/drivers/media/i2c/tvp7002.c +++ b/drivers/media/i2c/tvp7002.c @@ -35,6 +35,8 @@ #include <media/v4l2-ctrls.h> #include <media/v4l2-fwnode.h>
+#include <linux/nospec.h> + #include "tvp7002_reg.h"
MODULE_DESCRIPTION("TI TVP7002 Video and Graphics Digitizer driver"); @@ -784,7 +786,7 @@ static int tvp7002_enum_dv_timings(struct v4l2_subdev *sd, return -EINVAL;
/* Check requested format index is within range */ - if (timings->index >= NUM_TIMINGS) + if (!sanitize_index_nospec(timings->index, NUM_TIMINGS)) return -EINVAL;
timings->timings = tvp7002_timings[timings->index].timings; This patter is very common. So, it may be a good idea to unify both bounds checking and the serialization of instructions into a single function.
What do you think?
Thanks -- Gustavo
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