Messages in this thread | | | Subject | Re: [PATCH] kernel: sys: fix potential Spectre v1 | From | "Gustavo A. R. Silva" <> | Date | Fri, 18 May 2018 14:21:40 -0500 |
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On 05/18/2018 02:04 PM, Gustavo A. R. Silva wrote: > > > 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 */ >
Oops, it seems I sent the wrong patch. The function would look like this:
#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
Thanks -- Gustavo
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