Re: [PATCH v6 8/8] linux-user: Load pie executables at upper memory

[Akihiko Odaki]

On 2023/08/02 17:42, Helge Deller wrote:
On 8/2/23 09:49, Akihiko Odaki wrote:
On 2023/08/02 8:27, Helge Deller wrote:
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.

Why do you change guest addresses depending on the host?

The addresses are guest-addresses.
A 32-bit guest PIE can't be loaded at e.g. 0x5500000000,
while a 64-bit guest PIE needs to be loaded at 0x5500000000.

I mean, why do you use address 0x00000000 for 32-bit guest binaries on 
32-bit host while you use address 0x00300000 on 64-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 <del...@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..3bbfc108eb 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 - 0x20000000 + 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 c624feead0..3441198e21 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;

What if GUEST_ADDR_MAX < 0x1000000000?

this check affects 64-bit executables only where GUEST_ADDR_MAX is bigger
than that number. But I agree it's not directly visible from the code.
32-bit ones are taken care of where TASK_UNMAPPED_BASE is defined.

I think you can just return a hard error when mmap_next_start >= 
GUEST_ADDR_MAX.

Can't happen, but I will rewrite it.

+        }
+
+        if (TASK_UNMAPPED_BASE_PIE >= mmap_next_start) {
+            fprintf(stderr, "Memory too small for PIE executables.\n");

Perhaps it's better to use error_report() for new code.

Ok.

Helge