On Thu, Jun 28, 2018 at 9:30 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > On Wed, Jun 27, 2018 at 5:05 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: >> On Tue, Jun 26, 2018 at 7:29 PM, Catalin Marinas >> <catalin.marinas@xxxxxxx> wrote: >>> While I support this work, as a maintainer I'd like to understand >>> whether we'd be in a continuous chase of ABI breaks with every kernel >>> release or we have a better way to identify potential issues. Is there >>> any way to statically analyse conversions from __user ptr to long for >>> example? Or, could we get the compiler to do this for us? >> >> >> OK, got it, I'll try to figure out a way to find these conversions. > > I've prototyped a checker on top of clang static analyzer (initially > looked at sparse, but couldn't find any documentation or examples). > The results are here [1], search for "warning: user pointer cast". > Sharing in case anybody wants to take a look, will look at them myself > tomorrow. > > [1] https://gist.github.com/xairy/433edd5c86456a64026247cb2fef2115 So the checker reports ~100 different places where a __user pointer being casted. I've looked through them and found 3 places where we need to add untagging. Source code lines below come from 4.18-rc2+ (6f0d349d). Place 1: arch/arm64/mm/fault.c:302:34: warning: user pointer cast current->thread.fault_address = (unsigned long)info->si_addr; Compare a pointer with TASK_SIZE (1 << 48) to check whether it lies in the kernel or in user space. Need to untag the address before performing a comparison. Place 2: fs/namespace.c:2736:21: warning: user pointer cast size = TASK_SIZE - (unsigned long)data; A similar check performed by subtracting a pointer from TASK_SIZE. Need to untag before subtracting. Place 3: drivers/usb/core/devio.c:1407:29: warning: user pointer cast unsigned long uurb_start = (unsigned long)uurb->buffer; drivers/usb/core/devio.c:1636:31: warning: user pointer cast unsigned long uurb_start = (unsigned long)uurb->buffer; drivers/usb/core/devio.c:1715:30: warning: user pointer cast unsigned long uurb_start = (unsigned long)uurb->buffer; The device keeps list of mmapped areas and searches them for provided __user pointer. Need to untag before searching. There are also a few cases of memory syscalls operating on __user pointers instead of unsigned longs like mmap: ipc/shm.c:1355:23: warning: user pointer cast unsigned long addr = (unsigned long)shmaddr; ipc/shm.c:1566:23: warning: user pointer cast unsigned long addr = (unsigned long)shmaddr; mm/migrate.c:1586:10: warning: user pointer cast addr = (unsigned long)p; mm/migrate.c:1660:24: warning: user pointer cast unsigned long addr = (unsigned long)(*pages); If we don't add untagging to mmap, we probably don't need it here. The rest of reported places look fine as is. Full annotated results of running the checker are here [2]. I'll add the 3 patches with fixes to v5 of this patchset. Catalin, WDYT? [2] https://gist.github.com/xairy/aabda57741919df67d79895356ba9b58
