On Mon, Aug 16 2021 at 11:27, Davidlohr Bueso wrote: > On Mon, 16 Aug 2021, Huacai Chen wrote: > >>fault_in_user_writeable() should verify R/W access but only verify W. In >>most archs W implies R, but not true in MIPS and LoongArch, so fix it. > > Yuck for a find_vma() in futex.c. If this is a problem in MIPS, shouldn't > the fix be there? Furthermore it's stated that fault_in_user_writeable(): > > "Fault in user address and verify RW access" That seems to be wishful thinking given the fact that some architectures do not imply R for FLAG_FAULT_WRITE. > And you guys seem to have proposed it already: > > https://lore.kernel.org/linux-mips/20200630005845.1239974-1-liulichao@xxxxxxxxxxx/ That's surely one way to fix that. If that does not work for whatever reason, then we really don't want this find_vma() hack there, but rather something like: if (IS_ENABLED(CONFIG_ARCH_USER_FAULT_VOODOO) && get_user(&tmp, uaddr)) return -EFAULT; Thanks, tglx
