Messages in this thread | | | From | Dan Williams <> | Date | Tue, 15 May 2018 15:57:08 -0700 | Subject | Re: [PATCH] kernel: sys: fix potential Spectre v1 |
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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.
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