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Groups > linux.kernel > #1460833
| From | Kees Cook <keescook@chromium.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 2/2] arm: apply more __ro_after_init |
| Date | 2016-08-12 00:20 +0200 |
| Message-ID | <s56uu-1pD-23@gated-at.bofh.it> (permalink) |
| References | <rG2kq-6QU-9@gated-at.bofh.it> <s4HFM-12V-29@gated-at.bofh.it> <s4KNj-3c9-27@gated-at.bofh.it> <s50yK-5KE-23@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Thu, Aug 11, 2016 at 8:54 AM, Arnd Bergmann <arnd@arndb.de> wrote: > On Thursday, August 11, 2016 12:06:45 AM CEST Russell King - ARM Linux wrote: >> On Wed, Aug 10, 2016 at 09:41:23PM +0200, Arnd Bergmann wrote: >> > It might be better to start by making the fixed mapping readonly, >> > as KASLR doesn't protect that one at all, and change the TLS >> > code accordingly. >> >> I think that's impossible, because we gave userspace permission to >> read 0xffff0ff0 directly without using __kuser_get_tls. You're >> talking about potentially breaking userspace. >> >> If you disable kuser helpers, then the page becomes read-only and >> invisible to userspace anyway. So, everything is being done there >> which can be done - if you have kuser helpers enabled, then you >> lose some opportunities for these security improvements. > > What I meant was writing to the page through the linear mapping > rather than the virtual mapping at 0xffff0000 so we can leave that > one read-only (I did not consider whether that might cause cache > aliasing problems when reading from the other address). > > Your other point is more important though: if one really cares > about optimizing security here, they probably should disable > kuser helpers completely anyway. > > Kees, is that something you have on your radar already? It wasn't no. I will add it. :) -Kees -- Kees Cook Nexus Security
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Re: [PATCH 2/2] arm: apply more __ro_after_init Russell King - ARM Linux <linux@armlinux.org.uk> - 2016-08-11 01:10 +0200
Re: [PATCH 2/2] arm: apply more __ro_after_init Arnd Bergmann <arnd@arndb.de> - 2016-08-11 18:00 +0200
Re: [PATCH 2/2] arm: apply more __ro_after_init Kees Cook <keescook@chromium.org> - 2016-08-12 00:20 +0200
Re: [PATCH 2/2] arm: apply more __ro_after_init Russell King - ARM Linux <linux@armlinux.org.uk> - 2016-08-12 18:30 +0200
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