On Fri, Sep 27, 2019 at 03:38:44PM -0700, Linus Torvalds wrote: > On Fri, Sep 27, 2019 at 3:08 PM Nick Desaulniers > <ndesaulniers@xxxxxxxxxx> wrote: > > > > So get_user() was passed a bad value/pointer from userspace? Do you > > know which of the tree calls to get_user() from sock_setsockopt() is > > failing? (It's not immediately clear to me how this patch is at > > fault, vs there just being a bug in the source somewhere). > > Based on the error messages, the SO_PASSCRED ones are almost certainly > from the get_user() in net/core/sock.c: sock_setsockopt(), which just > does > > if (optlen < sizeof(int)) > return -EINVAL; > > if (get_user(val, (int __user *)optval)) > return -EFAULT; > > valbool = val ? 1 : 0; > > but it's the other messages imply that a lot of other cases are > failing too (ie the "Failed to bind netlink socket" is, according to > google, a bind() that fails with the same EFAULT error). > > There are probably even more failures that happen elsewhere and just > don't even syslog the fact. I'd guess that all get_user() calls just > fail, and those are the ones that happen to get printed out. > > Now, _why_ it would fail, I have ni idea. There are several inlines in > the arm uaccess.h file, and it depends on other headers like > <asm/domain.h> with more inlines still - eg get/set_domain() etc. > > Soem of that code is pretty subtle. They have fixed register usage > (but the asm macros actually check them). And the inline asms clobber > the link register, but they do seem to clearly _state_ that they > clobber it, so who knows. > > Just based on the EFAULT, I'd _guess_ that it's some interaction with > the domain access control register (so that get/set_domain() thing). > But I'm not even sure that code is enabled for the Rpi2, so who > knows.. FWIW, we've run into issues with CONFIG_OPTIMIZE_INLINING and local variables marked as 'register' where GCC would do crazy things and end up corrupting data, so I suspect the use of fixed registers in the arm uaccess functions is hitting something similar: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91111 Although this particular case couldn't be reproduced with GCC 9, prior versions of the compiler get it wrong so I'm very much opposed to enabling CONFIG_OPTIMIZE_INLINING by default on arm/arm64. Will
