Messages in this thread | | | Date | Mon, 22 Jul 2019 11:39:03 -0700 | From | Kees Cook <> | Subject | Re: [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace on i386 |
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On Mon, Jul 22, 2019 at 08:31:32PM +0200, Thomas Gleixner wrote: > On Mon, 22 Jul 2019, Kees Cook wrote: > > Just so I'm understanding: the vDSO change introduced code to make an > > actual syscall on i386, which for most seccomp filters would be rejected? > > No. The old x86 specific VDSO implementation had a fallback syscall as > well, i.e. clock_gettime(). On 32bit clock_gettime() uses the y2038 > endangered timespec. > > So when the VDSO was made generic we changed the internal data structures > to be 2038 safe right away. As a consequence the fallback syscall is not > clock_gettime(), it's clock_gettime64(). which seems to surprise seccomp.
Okay, it's didn't add a syscall, it just changed it. Results are the same: conservative filters suddenly start breaking due to the different call. (And now I see why Andy's alias suggestion would help...)
I'm not sure which direction to do with this. It seems like an alias list is a large hammer for this case, and a "seccomp-bypass when calling from vDSO" solution seems too fragile?
-- Kees Cook
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