[PATCH v5 3/3] linux-user: Load pie executables at upper memory

[Helge Deller <deller@gmx.de>]

Fix the elf loader to calculate a valid TASK_UNMAPPED_BASE address for all
32-bit architectures, based on the GUEST_ADDR_MAX constant.

Additionally modify the elf loader to load dynamic pie executables at
around:
~ 0x5500000000  for 64-bit guest binaries on 64-bit host,
- 0x00300000    for 32-bit guest binaries on 64-bit host, and
- 0x00000000    for 32-bit guest binaries on 32-bit host.

With this patch the Thread Sanitizer (TSan) application will work again,
as in commit aab613fb9597 ("linux-user: Update TASK_UNMAPPED_BASE for
aarch64").

Signed-off-by: Helge Deller <deller@gmx.de>
---
 linux-user/elfload.c |  6 ++++--
 linux-user/loader.h  | 12 ++++++++++++
 linux-user/mmap.c    | 35 ++++++++++++++++++-----------------
 3 files changed, 34 insertions(+), 19 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 47a118e430..8f5a79b537 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -3021,6 +3021,7 @@ static void load_elf_image(const char *image_name, int image_fd,
     struct elfhdr *ehdr = (struct elfhdr *)bprm_buf;
     struct elf_phdr *phdr;
     abi_ulong load_addr, load_bias, loaddr, hiaddr, error;
+    unsigned long load_offset = 0;
     int i, retval, prot_exec;
     Error *err = NULL;
     bool is_main_executable;
@@ -3121,6 +3122,7 @@ static void load_elf_image(const char *image_name, int image_fd,
              * select guest_base.  In this case we pass a size.
              */
             probe_guest_base(image_name, 0, hiaddr - loaddr);
+            load_offset = TASK_UNMAPPED_BASE_PIE;
         }
     }

@@ -3138,7 +3140,7 @@ static void load_elf_image(const char *image_name, int image_fd,
      * In both cases, we will overwrite pages in this range with mappings
      * from the executable.
      */
-    load_addr = target_mmap(loaddr, (size_t)hiaddr - loaddr + 1, PROT_NONE,
+    load_addr = target_mmap(loaddr + load_offset, (size_t)hiaddr - loaddr + 1, PROT_NONE,
                             MAP_PRIVATE | MAP_ANON | MAP_NORESERVE |
                             (is_main_executable ? MAP_FIXED : 0),
                             -1, 0);
@@ -3176,7 +3178,7 @@ static void load_elf_image(const char *image_name, int image_fd,
     info->start_data = -1;
     info->end_data = 0;
     /* possible start for brk is behind all sections of this ELF file. */
-    info->brk = TARGET_PAGE_ALIGN(hiaddr);
+    info->brk = TARGET_PAGE_ALIGN(load_offset + hiaddr);
     info->elf_flags = ehdr->e_flags;

     prot_exec = PROT_EXEC;
diff --git a/linux-user/loader.h b/linux-user/loader.h
index 59cbeacf24..d0e4ac4c07 100644
--- a/linux-user/loader.h
+++ b/linux-user/loader.h
@@ -18,6 +18,18 @@
 #ifndef LINUX_USER_LOADER_H
 #define LINUX_USER_LOADER_H

+/* where to map binaries? */
+#if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
+# define TASK_UNMAPPED_BASE_PIE 0x5500000000
+# define TASK_UNMAPPED_BASE	0x7000000000
+#elif HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 32
+# define TASK_UNMAPPED_BASE_PIE	0x00300000
+# define TASK_UNMAPPED_BASE	(GUEST_ADDR_MAX - 0xd000000 + 1)
+#else /* HOST_LONG_BITS == 32 && TARGET_ABI_BITS == 32 */
+# define TASK_UNMAPPED_BASE_PIE	0x00000000
+# define TASK_UNMAPPED_BASE	0x40000000
+#endif
+
 /*
  * Read a good amount of data initially, to hopefully get all the
  * program headers loaded.
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index 848d2fd4bb..59d52b93f9 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -23,6 +23,7 @@
 #include "user-internals.h"
 #include "user-mmap.h"
 #include "target_mman.h"
+#include "loader.h"

 static pthread_mutex_t mmap_mutex = PTHREAD_MUTEX_INITIALIZER;
 static __thread int mmap_lock_count;
@@ -295,23 +296,6 @@ static bool mmap_frag(abi_ulong real_start, abi_ulong start, abi_ulong last,
     return true;
 }

-#if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
-#ifdef TARGET_AARCH64
-# define TASK_UNMAPPED_BASE  0x5500000000
-#else
-# define TASK_UNMAPPED_BASE  0x4000000000
-#endif
-#elif HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 32
-#ifdef TARGET_HPPA
-# define TASK_UNMAPPED_BASE  0xfa000000
-#else
-# define TASK_UNMAPPED_BASE  0xe0000000
-#endif
-#else /* HOST_LONG_BITS == 32 && TARGET_ABI_BITS == 32 */
-# define TASK_UNMAPPED_BASE  0x40000000
-#endif
-abi_ulong mmap_next_start = TASK_UNMAPPED_BASE;
-
 unsigned long last_brk;

 /*
@@ -344,6 +328,23 @@ abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong align)
     abi_ulong addr;
     int wrapped, repeat;

+    static abi_ulong mmap_next_start;
+
+    /* initialize mmap_next_start if necessary */
+    if (!mmap_next_start) {
+        mmap_next_start = TASK_UNMAPPED_BASE;
+
+        /* do sanity checks on guest memory layout */
+        if (mmap_next_start >= GUEST_ADDR_MAX) {
+            mmap_next_start = GUEST_ADDR_MAX - 0x1000000000 + 1;
+        }
+
+        if (TASK_UNMAPPED_BASE_PIE >= mmap_next_start) {
+            fprintf(stderr, "Memory too small for PIE executables.\n");
+            exit(EXIT_FAILURE);
+        }
+    }
+
     align = MAX(align, qemu_host_page_size);

     /* If 'start' == 0, then a default start address is used. */
--
2.41.0