[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack(
From: |
Brad Smith |
Subject: |
Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD |
Date: |
Tue, 9 Oct 2018 10:19:13 -0400 |
User-agent: |
Mutt/1.10.1 (2018-07-13) |
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 <address@hidden>
> >
> >
> > 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();
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, (continued)
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, Kamil Rytarowski, 2018/10/09
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, Peter Maydell, 2018/10/09
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, Kamil Rytarowski, 2018/10/09
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, Brad Smith, 2018/10/10
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, Peter Maydell, 2018/10/11
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, Kamil Rytarowski, 2018/10/11
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, Brad Smith, 2018/10/11
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, Kamil Rytarowski, 2018/10/11
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, Brad Smith, 2018/10/11
- Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD, Kamil Rytarowski, 2018/10/13
Re: [Qemu-devel] [PATCH] oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD,
Brad Smith <=