[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC PATCH] x86/pagewalk: Honor SMAP_CHECK_DISABLED
On 07/05/2018 20:57, Jason Andryuk wrote: > commit 4c5d78a10dc89427140a50a1df5a0b8e9f073e82 (x86/pagewalk: > Re-implement the pagetable walker) removed honoring the > smap_check_policy of the running VCPU. guest_walk_tables is used by > copy_{to,from}_guest for HVMs, so it is called when the hypervisor is > copying data and SMAP is inappropriate to enforce. > > The out-of-tree v4v hypercall copies a domain's source buffer into a > different domain's destination ring. For an HVM, the kernel makes the > hypercall from ring 0, so the userspace buffer access looks like a SMAP > violation. In Xen 4.6, v4v could set SMAP_CHECK_DISABLED to avoid this > SMAP failure, but that no longer works since the re-write. > > Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx> I'm sorry, but no. It is never appropriate to ignore the guest paging settings. The correct fix here is in the kernel, to surround the v4v hypercall handler with stac/clac to whitelist userspace accesses. See the implementation of the privcmd hypercall which already does this. If I could go back in time and nack the introduction of smap_check_policy, I would. As it stands, I'm (slowly) removing its use, and will eventually delete it. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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