base-linux: disable ASLR for child processes

ASLR collides with the libc's fork mechanism on 32-bit. In particular,
the tool_chain_auto.run scenario would sporadically fail while mirroring
the parent's address space.

Fixes #3710

repos/base-linux/src/core/include/core_linux_syscalls.h

@@ -101,11 +101,13 @@ inline int lx_ioctl_iomem(int fd, unsigned long phys, Genode::size_t offset)
 	return lx_syscall(SYS_ioctl, fd, _IOW('g', 1, void *), &range);
 }
 
+
 inline int lx_ioctl_irq(int fd, int irq)
 {
 	return lx_syscall(SYS_ioctl, fd, _IOW('g', 2, int*), &irq);
 }
 
+
 /**************************************
  ** Process creation and destruction **
  **************************************/
@@ -161,6 +163,23 @@ inline int lx_pollpid()
 }
 
 
+/**
+ * Disable address-space layout randomization for child processes
+ *
+ * The virtual address space layout is managed by Genode, not the kernel.
+ * Otherwise, the libc's fork mechanism could not work on Linux.
+ */
+inline void lx_disable_aslr()
+{
+	/* defined in linux/personality.h */
+	enum { ADDR_NO_RANDOMIZE = 0x0040000UL };
+
+	unsigned long const orig_flags = lx_syscall(SYS_personality, 0xffffffff);
+
+	(void)lx_syscall(SYS_personality, orig_flags | ADDR_NO_RANDOMIZE);
+}
+
+
 /********************************************
  ** Communication over Unix-domain sockets **
  ********************************************/

repos/base-linux/src/core/platform.cc

@@ -91,6 +91,9 @@ static void sigchld_handler(int)
 Platform::Platform()
 : _core_mem_alloc(nullptr)
 {
+	/* make 'mmap' behave deterministically */
+	lx_disable_aslr();
+
 	/* catch control-c */
 	lx_sigaction(LX_SIGINT, sigint_handler, false);