[Qemu-devel] [PATCH] linux-user: use default mmap_min_addr 65536 when /proc/sys/vm/mmap_min_addr cannot be read

[Martin Jansa]

* 65536 is default at least for ubuntu and fedora.
* after 
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=0e1a6ef2dea88101b056b6d9984f3325c5efced3
  it's not readable by normal user on many systems
* there is patch to enable read-only access again
  
http://git.kernel.org/?p=linux/kernel/git/jmorris/security-testing-2.6.git;a=commitdiff;h=822cceec7248013821d655545ea45d1c6a9d15b3
  but that's not applied in many distributions
* please consider this workaround

Signed-off-by: Martin Jansa <martin.ja...@gmail.com>
---
 linux-user/main.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/linux-user/main.c b/linux-user/main.c
index 18b52c0..94b6465 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -2891,6 +2891,7 @@ int main(int argc, char **argv, char **envp)
      * When loading the ELF image to determine whether guest_base
      * is needed.  It is also used in mmap_find_vma.
      */
+#define MMAP_MIN_ADDR_DEFAULT 65536
     {
         FILE *fp;
 
@@ -2899,8 +2900,14 @@ int main(int argc, char **argv, char **envp)
             if (fscanf(fp, "%lu", &tmp) == 1) {
                 mmap_min_addr = tmp;
                 qemu_log("host mmap_min_addr=0x%lx\n", mmap_min_addr);
+            } else {
+                qemu_log("cannot read value from /proc/sys/vm/mmap_min_addr, 
assuming %d\n", MMAP_MIN_ADDR_DEFAULT);
+                mmap_min_addr = MMAP_MIN_ADDR_DEFAULT;
             }
             fclose(fp);
+        } else {
+            qemu_log("cannot open /proc/sys/vm/mmap_min_addr for reading, 
assuming %d\n", MMAP_MIN_ADDR_DEFAULT);
+            mmap_min_addr = MMAP_MIN_ADDR_DEFAULT;
         }
     }
 
-- 
1.7.1