Messages in this thread | | | From | Andy Lutomirski <> | Date | Fri, 16 Mar 2018 00:38:15 +0000 | Subject | Re: [PATCH v2 00/36] remove in-kernel syscall invocations (part 1) |
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On Thu, Mar 15, 2018 at 9:02 PM, Arnd Bergmann <arnd@arndb.de> wrote: > On Thu, Mar 15, 2018 at 8:04 PM, Dominik Brodowski > <linux@dominikbrodowski.net> wrote: >> Here is a re-spin of the first set of patches which reduce the number of >> syscall invocations from within the kernel; the RFC may be found at >> >> The rationale for this change is described in patch 1 as follows: >> >> The syscall entry points to the kernel defined by SYSCALL_DEFINEx() >> and COMPAT_SYSCALL_DEFINEx() should only be called from userspace >> through kernel entry points, but not from the kernel itself. This >> will allow cleanups and optimizations to the entry paths *and* to >> the parts of the kernel code which currently need to pretend to be >> userspace in order to make use of syscalls. >> >> The whole series can be found at >> >> https://git.kernel.org/pub/scm/linux/kernel/git/brodo/linux.git syscalls-next >> >> and will be submitted for merging for the v4.17-rc1 cycle, probably together >> with another batch of related patches I hope to send out tomorrow as a RFC. > > Nice work! > > I've already commented on a few patches that now have a kernel-internal > helper function that takes a __user pointer. I think those are all only used > in the early boot code (initramfs etc) that runs before we set_fs() to the > user address space, but it also causes warnings with sparse. If we > can change all of them to take kernel pointers, that would let us avoid > the sparse warnings and start running with a normal user address space > view. Unfortunately, some of the syscall seem to be harder to change to > that than others, so not sure if it's worth the effort.
It would be fantastic to get rid of set_fs() entirely and make it impossible for get_user(), etc to ever access kernel memory. And this effort is necessary to ever achieve that.
I don't think this patch series should wait for any of these cleanups, though. We need these patches to change the x86_64 internal syscall function signature, which we've been wanting to do for a little while.
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