On 02/03/2020 19.31, Jann Horn wrote: > On Mon, Mar 2, 2020 at 7:17 PM Alexander Potapenko <glider@xxxxxxxxxx> wrote: >> On Mon, Mar 2, 2020 at 3:00 PM Joe Perches <joe@xxxxxxxxxxx> wrote: >>> >>> So? CONFIG_INIT_STACK_ALL by design slows down code. >> Correct. >> >>> This marking would likely need to be done for nearly all >>> 3000+ copy_from_user entries. >> Unfortunately, yes. I was just hoping to do so for a handful of hot >> cases that we encounter, but in the long-term a compiler solution must >> supersede them. >> >>> Why not try to get something done on the compiler side >>> to mark the function itself rather than the uses? >> This is being worked on in the meantime as well (see >> http://lists.llvm.org/pipermail/cfe-dev/2020-February/064633.html) >> Do you have any particular requisitions about how this should look on >> the source level? > > Just thinking out loud: Should this be a function attribute, or should > it be a builtin - something like __builtin_assume_initialized(ptr, > len)? That would make it also work for macros, But with macros (and static inlines), the compiler sees all the initialization being done, no? and it might simplify > the handling of inlining in the compiler. And you wouldn't need such a > complicated attribute that refers to function arguments by index and > such. Does copy_from_user guarantee to zero-initialize the remaining buffer if copying fails partway through? Otherwise it will be hard for the compiler to make use of an annotation such as __assume_initialized(buf, size - ret_from_cfu) - it will have to say "ok, the caller is bailing out unless ret_from_cfu is 0, and in that case, yes, the whole local struct variable is indeed initialized". And we can't make the annotation unconditionally __assume_initialized(buf, size) [unless c_f_u comes with that guarantee] because we don't know that all callers of c_f_u() bail out on non-zero. Somewhat related: I've long wanted a bunch of function attributes __may_read(ptr, bytes) __may_write(ptr, bytes) __will_write(ptr, bytes) The first could be used to warn about passing an uninitialized or too-small buffer (e.g. struct pollfd fds[4]; poll(fds, sizeof(fds), ...) // whoops, should have been ARRAY_SIZE) the second also for warning about a too-small buffer, and the third would essentially be the same as __assume_initializes. Perhaps with some sanitization option the compiler could also instrument the function definition to not read/write beyond the area declared via those attributes. But the attribute syntax doesn't currently allow complex expressions in terms of the parameter names; I'd want to annotate poll as int poll(struct pollfd *fds, nfds_t nfds, int to) __may_rw(fds, nfds * sizeof(*fds)) Rasmus _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
