On 07.10.2018 17:37, Brad Smith wrote: > Use MAP_STACK in qemu_alloc_stack() on OpenBSD. > > Added to -current and will be in our soon to be 6.4 release. > > MAP_STACK Indicate that the mapping is used as a stack. This > flag must be used in combination with MAP_ANON and > MAP_PRIVATE. > > Implement MAP_STACK option for mmap(). Synchronous faults (pagefault and > syscall) confirm the stack register points at MAP_STACK memory, otherwise > SIGSEGV is delivered. sigaltstack() and pthread_attr_setstack() are modified > to create a MAP_STACK sub-region which satisfies alignment requirements. > Observe that MAP_STACK can only be set/cleared by mmap(), which zeroes the > contents of the region -- there is no mprotect() equivalent operation, so > there is no MAP_STACK-adding gadget. > > > Signed-off-by: Brad Smith <b...@comstyle.com> > > > diff --git a/util/oslib-posix.c b/util/oslib-posix.c > index fbd0dc8c57..51e9a012c2 100644 > --- a/util/oslib-posix.c > +++ b/util/oslib-posix.c > @@ -611,7 +611,11 @@ void *qemu_alloc_stack(size_t *sz) > *sz += pagesz; > > ptr = mmap(NULL, *sz, PROT_READ | PROT_WRITE, > - MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > + MAP_PRIVATE | MAP_ANONYMOUS > +#ifdef MAP_STACK > + | MAP_STACK > +#endif > + , -1, 0); > if (ptr == MAP_FAILED) { > perror("failed to allocate memory for stack"); > abort(); >
Can we handle it differently, storing MAP_* flags in a variable: int flags = MAP_PRIVATE | MAP_ANONYMOUS; #ifdef MAP_STACK flags |= MAP_STACK; #endif ptr = mmap(NULL, *sz, PROT_READ | PROT_WRITE, flags, -1, 0); This way it will look nicer as we won't ifdef the middle of a function call.
signature.asc
Description: OpenPGP digital signature