On Fri, Mar 9, 2018 at 9:31 AM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > On Fri, Mar 9, 2018 at 4:53 PM, Catalin Marinas <catalin.marinas@xxxxxxx> wrote: >> On Fri, Mar 09, 2018 at 03:02:01PM +0100, Andrey Konovalov wrote: >>> Memory subsystem syscalls accept user addresses as arguments, but don't use >>> copy_from_user and other similar functions, so we need to handle this case >>> separately. >>> >>> Untag user pointers passed to madvise, mbind, get_mempolicy, mincore, >>> mlock, mlock2, brk, mmap_pgoff, old_mmap, munmap, remap_file_pages, >>> mprotect, pkey_mprotect, mremap and msync. >>> >>> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> >> >> Please keep the cc list small (maybe linux-arch, linux-arm-kernel) as >> I'm sure some lists would consider this spam. > > OK. > >> >>> mm/madvise.c | 2 ++ >>> mm/mempolicy.c | 6 ++++++ >>> mm/mincore.c | 2 ++ >>> mm/mlock.c | 5 +++++ >>> mm/mmap.c | 9 +++++++++ >>> mm/mprotect.c | 2 ++ >>> mm/mremap.c | 2 ++ >>> mm/msync.c | 3 +++ >> >> I'm not yet convinced these functions need to allow tagged pointers. >> They are not doing memory accesses but rather dealing with the memory >> range, hence an untagged pointer is better suited. There is probably a >> reason why the "start" argument is "unsigned long" vs "void __user *" >> (in the kernel, not the man page). > > So that would make the user to untag pointers before passing to these syscalls. > > Evgeniy, would that be possible to untag pointers in HWASan before > using memory subsystem syscalls? Is there a reason for untagging them > in the kernel? Generally, no. It's possible to intercept a libc call using symbol interposition, but I don't know how to rewrite arguments of a raw system call other than through ptrace, and that creates more problems than it solves. AFAIU, it's valid for a program to pass an address obtained from malloc or, better, posix_memalign to an mm syscall like mprotect(). These arguments are pointers from the userspace point of view.
