hurd: Map brk non-executable

The rest of the heap (backed by individual pages) is already mapped RW.
Mapping these pages RWX presents a security hazard.

Also, in another branch memory gets allocated using vm_allocate, which
sets memory protection to VM_PROT_DEFAULT (which is RW). The mismatch
between protections prevents Mach from coalescing the VM map entries.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
Message-Id: <20230625231751.404120-2-bugaevc@gmail.com>

diff --git a/sysdeps/mach/hurd/brk.c b/sysdeps/mach/hurd/brk.c
index f1349495f5575a2a8c4ed09efd9cc85a06da8cb9..3a335194f5dca18a88a2c3c9dc584a9eac016d65 100644 (file)
--- a/sysdeps/mach/hurd/brk.c
+++ b/sysdeps/mach/hurd/brk.c
@@ -106,7 +106,7 @@ _hurd_set_brk (vm_address_t addr)
        /* First finish allocation.  */
        err = __vm_protect (__mach_task_self (), pagebrk,
                            alloc_start - pagebrk, 0,
-                           VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE);
+                           VM_PROT_READ|VM_PROT_WRITE);
       if (! err)
        _hurd_brk = alloc_start;
 
@@ -120,7 +120,7 @@ _hurd_set_brk (vm_address_t addr)
   else
     /* Make the memory accessible.  */
     err = __vm_protect (__mach_task_self (), pagebrk, pagend - pagebrk,
-                       0, VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE);
+                       0, VM_PROT_READ|VM_PROT_WRITE);
 
   if (err)
     return __hurd_fail (err);