From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42488) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1g9srB-0006JX-EY for qemu-devel@nongnu.org; Tue, 09 Oct 2018 10:19:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1g9sr7-0003hs-DV for qemu-devel@nongnu.org; Tue, 09 Oct 2018 10:19:27 -0400 Received: from speedy.comstyle.com ([2001:470:1d:8c::2]:13401 helo=mail.comstyle.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1g9sr5-0003eF-CH for qemu-devel@nongnu.org; Tue, 09 Oct 2018 10:19:23 -0400 Date: Tue, 9 Oct 2018 10:19:13 -0400 From: Brad Smith Message-ID: <20181009141912.GA76167@humpty.home.comstyle.com> References: <20181007153731.GA32288@humpty.home.comstyle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kamil Rytarowski Cc: qemu-devel@nongnu.org On Tue, Oct 09, 2018 at 03:52:30PM +0200, Kamil Rytarowski wrote: > 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 > > > > > > 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. How about the following? diff --git a/util/oslib-posix.c b/util/oslib-posix.c index fbd0dc8c57..f8ee349c9c 100644 --- a/util/oslib-posix.c +++ b/util/oslib-posix.c @@ -596,6 +596,7 @@ pid_t qemu_fork(Error **errp) void *qemu_alloc_stack(size_t *sz) { void *ptr, *guardpage; + int flags; #ifdef CONFIG_DEBUG_STACK_USAGE void *ptr2; #endif @@ -610,8 +611,12 @@ void *qemu_alloc_stack(size_t *sz) /* allocate one extra page for the guard page */ *sz += pagesz; - ptr = mmap(NULL, *sz, PROT_READ | PROT_WRITE, - MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + flags = MAP_PRIVATE | MAP_ANONYMOUS; +#ifdef MAP_STACK + flags |= MAP_STACK; +#endif + + ptr = mmap(NULL, *sz, PROT_READ | PROT_WRITE, flags, -1, 0); if (ptr == MAP_FAILED) { perror("failed to allocate memory for stack"); abort();