[Qemu-devel] [PATCH 2/2] linux-user: Use init_guest_space when -R and -B are specified

[Meador Inge]

Modify the driver to initialize the guest address space when -R or -B
is specified so that the reserved memory space can be probed.  Calling
'mmap' just once as is currently done is not guaranteed to succeed since
the host address space validation might fail.

Signed-off-by: Meador Inge <address@hidden>
---
 linux-user/elfload.c |   57 +++++++++++++++++++++++++++++++++++++++++++-------
 linux-user/main.c    |   35 +++++-------------------------
 linux-user/qemu.h    |    6 -----
 3 files changed, 55 insertions(+), 43 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 44b4bdb..8de96bc 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -332,9 +332,17 @@ enum
     ARM_HWCAP_ARM_VFPv3D16  = 1 << 13,
 };
 
-#define TARGET_HAS_GUEST_VALIDATE_BASE
-/* We want the opportunity to check the suggested base */
-bool guest_validate_base(unsigned long guest_base)
+#define TARGET_HAS_VALIDATE_GUEST_SPACE
+/* Return 1 if the proposed guest space is suitable for the guest.
+ * Return 0 if the proposed guest space isn't suitable, but another
+ * address space should be tried.
+ * Return -1 if there is no way the proposed guest space can be
+ * valid regardless of the base.
+ * The guest code may leave a page mapped and populate it if the
+ * address is suitable.
+ */
+static int validate_guest_space(unsigned long guest_base,
+                                unsigned long guest_size)
 {
     unsigned long real_start, test_page_addr;
 
@@ -342,6 +350,15 @@ bool guest_validate_base(unsigned long guest_base)
      * commpage at 0xffff0fxx
      */
     test_page_addr = guest_base + (0xffff0f00 & qemu_host_page_mask);
+
+    /* If the commpage lies within the already allocated guest space,
+     * then there is no way we can allocate it.
+     */
+    if (test_page_addr >= guest_base
+       && test_page_addr <= (guest_base + guest_size)) {
+         return -1;
+    }
+
     /* Note it needs to be writeable to let us initialise it */
     real_start = (unsigned long)
                  mmap((void *)test_page_addr, qemu_host_page_size,
@@ -1377,9 +1394,10 @@ static abi_ulong create_elf_tables(abi_ulong p, int 
argc, int envc,
     return sp;
 }
 
-#ifndef TARGET_HAS_GUEST_VALIDATE_BASE
+#ifndef TARGET_HAS_VALIDATE_GUEST_SPACE
 /* If the guest doesn't have a validation function just agree */
-bool guest_validate_base(unsigned long guest_base)
+static int validate_guest_space(unsigned long guest_base,
+                                unsigned long guest_size)
 {
     return 1;
 }
@@ -1400,7 +1418,7 @@ unsigned long init_guest_space(unsigned long host_start,
     /* If just a starting address is given, then just verify that
      * address.  */
     if (host_start && !host_size) {
-        if (guest_validate_base(host_start)) {
+        if (validate_guest_space(host_start, host_size) == 1) {
             return host_start;
         } else {
             return (unsigned long)-1;
@@ -1417,6 +1435,8 @@ unsigned long init_guest_space(unsigned long host_start,
     /* Otherwise, a non-zero size region of memory needs to be mapped
      * and validated.  */
     while (1) {
+        unsigned long real_size = host_size;
+
         /* Do not use mmap_find_vma here because that is limited to the
          * guest address space.  We are going to make the
          * guest address space fit whatever we're given.
@@ -1427,8 +1447,27 @@ unsigned long init_guest_space(unsigned long host_start,
             return (unsigned long)-1;
         }
 
-        if ((real_start == current_start) && guest_validate_base(real_start)) {
-            break;
+        /* Ensure the address is properly aligned.  */
+        if (real_start & ~qemu_host_page_mask) {
+            munmap((void *)real_start, host_size);
+            real_size = host_size + qemu_host_page_size;
+            real_start = (unsigned long)
+                mmap((void *)real_start, real_size, PROT_NONE, flags, -1, 0);
+            if (real_start == (unsigned long)-1) {
+                return (unsigned long)-1;
+            }
+            real_start = HOST_PAGE_ALIGN(real_start);
+        }
+
+        /* Check to see if the address is valid.  */
+        if (!host_start || real_start == current_start) {
+            int valid = validate_guest_space(real_start, real_size);
+            if (valid == 1) {
+                break;
+            } else if (valid == -1) {
+                return (unsigned long)-1;
+            }
+            /* valid == 0, so try again. */
         }
 
         /* That address didn't work.  Unmap and try a different one.
@@ -1450,6 +1489,8 @@ unsigned long init_guest_space(unsigned long host_start,
         }
     }
 
+    qemu_log("Reserved 0x%lx bytes of guest address space\n", host_size);
+
     return real_start;
 }
 
diff --git a/linux-user/main.c b/linux-user/main.c
index d0e0e4f..ef56c09 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -3425,39 +3425,16 @@ int main(int argc, char **argv, char **envp)
      */
     guest_base = HOST_PAGE_ALIGN(guest_base);
 
-    if (reserved_va) {
-        void *p;
-        int flags;
-
-        flags = MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE;
-        if (have_guest_base) {
-            flags |= MAP_FIXED;
-        }
-        p = mmap((void *)guest_base, reserved_va, PROT_NONE, flags, -1, 0);
-        if (p == MAP_FAILED) {
+    if (reserved_va || have_guest_base) {
+        guest_base = init_guest_space(guest_base, reserved_va,
+                                      have_guest_base);
+        if (guest_base == (unsigned long)-1) {
             fprintf(stderr, "Unable to reserve guest address space\n");
             exit(1);
         }
-        guest_base = (unsigned long)p;
-        /* Make sure the address is properly aligned.  */
-        if (guest_base & ~qemu_host_page_mask) {
-            munmap(p, reserved_va);
-            p = mmap((void *)guest_base, reserved_va + qemu_host_page_size,
-                     PROT_NONE, flags, -1, 0);
-            if (p == MAP_FAILED) {
-                fprintf(stderr, "Unable to reserve guest address space\n");
-                exit(1);
-            }
-            guest_base = HOST_PAGE_ALIGN((unsigned long)p);
-        }
-        qemu_log("Reserved 0x%lx bytes of guest address space\n", reserved_va);
-        mmap_next_start = reserved_va;
-    }
 
-    if (reserved_va || have_guest_base) {
-        if (!guest_validate_base(guest_base)) {
-            fprintf(stderr, "Guest base/Reserved VA rejected by guest code\n");
-            exit(1);
+        if (reserved_va) {
+            mmap_next_start = reserved_va;
         }
     }
 #endif /* CONFIG_USE_GUEST_BASE */
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index c23dd8a..bdc82ff 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -204,12 +204,6 @@ int get_osversion(void);
 void fork_start(void);
 void fork_end(int child);
 
-/* Return true if the proposed guest_base is suitable for the guest.
- * The guest code may leave a page mapped and populate it if the
- * address is suitable.
- */
-bool guest_validate_base(unsigned long guest_base);
-
 /* Creates the initial guest address space in the host memory space using the
  * given host start address hint and size.  If fixed is specified, then the
  * mapped address space must start at host_start.  If host_start and host_size
-- 
1.7.7.6