Patchwork [09/14] linux-user: Put the stack guard page at the top.

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Submitter Richard Henderson
Date April 4, 2010, 10:14 p.m.
Message ID <9b2d67800c4c8cc9a491560fd101e6276f07ecb4.1272483393.git.rth@twiddle.net>
Download mbox | patch
Permalink /patch/51236/
State New
Headers show

Comments

Richard Henderson - April 4, 2010, 10:14 p.m.
There are no supported stack-grows-up targets.  We were putting
the guard page at the highest address, i.e. the bottom of the stack.
Use the maximum of host and guest page size for the guard size.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 linux-user/elfload.c |   29 ++++++++++++++++-------------
 1 files changed, 16 insertions(+), 13 deletions(-)

Patch

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 5853a30..464160a 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -1002,28 +1002,31 @@  static abi_ulong copy_elf_strings(int argc,char ** argv, void **page,
 static abi_ulong setup_arg_pages(abi_ulong p, struct linux_binprm *bprm,
                                  struct image_info *info)
 {
-    abi_ulong stack_base, size, error;
+    abi_ulong stack_base, size, error, guard;
     int i;
 
     /* Create enough stack to hold everything.  If we don't use
-     * it for args, we'll use it for something else...
-     */
+       it for args, we'll use it for something else.  */
     size = guest_stack_size;
-    if (size < MAX_ARG_PAGES*TARGET_PAGE_SIZE)
+    if (size < MAX_ARG_PAGES*TARGET_PAGE_SIZE) {
         size = MAX_ARG_PAGES*TARGET_PAGE_SIZE;
-    error = target_mmap(0,
-                        size + qemu_host_page_size,
-                        PROT_READ | PROT_WRITE,
-                        MAP_PRIVATE | MAP_ANONYMOUS,
-                        -1, 0);
+    }
+    guard = TARGET_PAGE_SIZE;
+    if (guard < qemu_real_host_page_size) {
+        guard = qemu_real_host_page_size;
+    }
+
+    error = target_mmap(0, size + guard, PROT_READ | PROT_WRITE,
+                        MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
     if (error == -1) {
-        perror("stk mmap");
+        perror("mmap stack");
         exit(-1);
     }
-    /* we reserve one extra page at the top of the stack as guard */
-    target_mprotect(error + size, qemu_host_page_size, PROT_NONE);
 
-    stack_base = error + size - MAX_ARG_PAGES*TARGET_PAGE_SIZE;
+    /* We reserve one extra page at the top of the stack as guard.  */
+    target_mprotect(error, guard, PROT_NONE);
+
+    stack_base = error + guard + size - MAX_ARG_PAGES*TARGET_PAGE_SIZE;
     p += stack_base;
 
     for (i = 0 ; i < MAX_ARG_PAGES ; i++) {