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authorBrad Smith <brad@comstyle.com>2018-10-19 08:52:39 -0400
committerPeter Maydell <peter.maydell@linaro.org>2018-11-06 10:52:23 +0000
commitfc3d1bad1edf08871275cf469a64e12dae4eba96 (patch)
tree03bd93a3699835cb4d0e4938dbe05313d8db2b84 /util
parent03c1ca1c51783603d42eb0f91d35961f0f4b4947 (diff)
oslib-posix: Use MAP_STACK in qemu_alloc_stack() on OpenBSD
Use MAP_STACK in qemu_alloc_stack() on OpenBSD. Added to our 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 <brad@comstyle.com> Reviewed-by: Kamil Rytarowski <n54@gmx.com> Reviewed-by: Peter Maydell <peter.maydell@linaro.org> Message-id: 20181019125239.GA13884@humpty.home.comstyle.com Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Diffstat (limited to 'util')
-rw-r--r--util/oslib-posix.c15
1 files changed, 13 insertions, 2 deletions
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index fbd0dc8c57..c1bee2a581 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 +611,18 @@ 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;
+#if defined(MAP_STACK) && defined(__OpenBSD__)
+ /* Only enable MAP_STACK on OpenBSD. Other OS's such as
+ * Linux/FreeBSD/NetBSD have a flag with the same name
+ * but have differing functionality. OpenBSD will SEGV
+ * if it spots execution with a stack pointer pointing
+ * at memory that was not allocated with 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();