On Wed, Jun 27, 2018 at 04:08:09PM +0100, Ramana Radhakrishnan wrote: > On 27/06/2018 16:05, Andrey Konovalov wrote: > > On Tue, Jun 26, 2018 at 7:29 PM, Catalin Marinas > > <catalin.marinas@xxxxxxx> wrote: > >> On Tue, Jun 26, 2018 at 02:47:50PM +0200, Andrey Konovalov wrote: > >>> On Wed, Jun 20, 2018 at 5:24 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > >>>> arm64 has a feature called Top Byte Ignore, which allows to embed pointer > >>>> tags into the top byte of each pointer. Userspace programs (such as > >>>> HWASan, a memory debugging tool [1]) might use this feature and pass > >>>> tagged user pointers to the kernel through syscalls or other interfaces. > >>>> > >>>> This patch makes a few of the kernel interfaces accept tagged user > >>>> pointers. The kernel is already able to handle user faults with tagged > >>>> pointers and has the untagged_addr macro, which this patchset reuses. > >>>> > >>>> We're not trying to cover all possible ways the kernel accepts user > >>>> pointers in one patchset, so this one should be considered as a start. > >>>> > >>>> Thanks! > >>>> > >>>> [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html > >>> > >>> Is there anything I should do to move forward with this? > >>> > >>> I've received zero replies to this patch set (v3 and v4) over the last > >>> month. > >> > >> The patches in this series look fine but my concern is that they are not > >> sufficient and we don't have (yet?) a way to identify where such > >> annotations are required. You even say in patch 6 that this is "some > >> initial work for supporting non-zero address tags passed to the kernel". > >> Unfortunately, merging (or relaxing) an ABI without a clear picture is > >> not really feasible. > >> > >> 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. > > This sounds like the kind of thing we should be able to get sparse to do > already, no ? It's been many years since I last looked at it but I > thought sparse was the tool of choice in the kernel to do this kind of > checking. sparse is indeed an option. The current implementation doesn't warn on an explicit cast from (void __user *) to (unsigned long) since that's a valid thing in the kernel. I couldn't figure out if there's any other __attribute__ that could be used to warn of such conversion. -- Catalin
