The mmap2() syscall allows 32-bit guests to specify the offset into a
file in page units (instead of bytes, as done by mmap(2)).
On physical machines this allows 32-bit applications to map such parts
of large files which are stored beyond the 4GB limit.

Allow the same behaviour when emulating 32-bit guests with qemu.

For that switch the mmap2() function to always take an abi_ullong
(64-bit) offset parameter for target_mmap() and mmap_frag() to avoid an
arithmetical overflow when shifing a 32-bit offset parameter by
12 bits (=PAGE_SHIFT) and thus possibly overflow the abi_ulong (32-bit)
type.

Signed-off-by: Helge Deller <deller@gmx.de>
---
 linux-user/mmap.c      | 9 +++++----
 linux-user/syscall.c   | 2 +-
 linux-user/user-mmap.h | 2 +-
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index 2692936773..2750146758 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -192,7 +192,7 @@ error:
 /* map an incomplete host page */
 static int mmap_frag(abi_ulong real_start,
                      abi_ulong start, abi_ulong end,
-                     int prot, int flags, int fd, abi_ulong offset)
+                     int prot, int flags, int fd, abi_ullong offset)
 {
     abi_ulong real_end, addr;
     void *host_start;
@@ -436,10 +436,11 @@ abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong align)

 /* NOTE: all the constants are the HOST ones */
 abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
-                     int flags, int fd, abi_ulong offset)
+                     int flags, int fd, abi_ullong offset)
 {
-    abi_ulong ret, end, real_start, real_end, retaddr, host_offset, host_len,
+    abi_ulong ret, end, real_start, real_end, retaddr, host_len,
               passthrough_start = -1, passthrough_end = -1;
+    abi_ullong host_offset;
     int page_flags, host_prot;

     mmap_lock();
@@ -627,7 +628,7 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
         /* map the middle (easier) */
         if (real_start < real_end) {
             void *p;
-            unsigned long offset1;
+            off_t offset1;
             if (flags & MAP_ANONYMOUS)
                 offset1 = 0;
             else
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 9e9317237d..5ebc502f71 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -10427,7 +10427,7 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
 #endif
         ret = target_mmap(arg1, arg2, arg3,
                           target_to_host_bitmask(arg4, mmap_flags_tbl),
-                          arg5, arg6 << MMAP_SHIFT);
+                          arg5, ((abi_ullong)arg6) << MMAP_SHIFT);
         return get_errno(ret);
 #endif
     case TARGET_NR_munmap:
diff --git a/linux-user/user-mmap.h b/linux-user/user-mmap.h
index 480ce1c114..72e99000d9 100644
--- a/linux-user/user-mmap.h
+++ b/linux-user/user-mmap.h
@@ -20,7 +20,7 @@

 int target_mprotect(abi_ulong start, abi_ulong len, int prot);
 abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
-                     int flags, int fd, abi_ulong offset);
+                     int flags, int fd, abi_ullong offset);
 int target_munmap(abi_ulong start, abi_ulong len);
 abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
                        abi_ulong new_size, unsigned long flags,
--
2.41.0

On 7/7/23 14:19, Helge Deller wrote:
> The mmap2() syscall allows 32-bit guests to specify the offset into a
> file in page units (instead of bytes, as done by mmap(2)).
> On physical machines this allows 32-bit applications to map such parts
> of large files which are stored beyond the 4GB limit.
> 
> Allow the same behaviour when emulating 32-bit guests with qemu.
> 
> For that switch the mmap2() function to always take an abi_ullong
> (64-bit) offset parameter for target_mmap() and mmap_frag() to avoid an
> arithmetical overflow when shifing a 32-bit offset parameter by
> 12 bits (=PAGE_SHIFT) and thus possibly overflow the abi_ulong (32-bit)
> type.
> 
> Signed-off-by: Helge Deller<deller@gmx.de>
> ---
>   linux-user/mmap.c      | 9 +++++----
>   linux-user/syscall.c   | 2 +-
>   linux-user/user-mmap.h | 2 +-
>   3 files changed, 7 insertions(+), 6 deletions(-)

https://patchew.org/QEMU/20230630132159.376995-1-richard.henderson@linaro.org/20230630132159.376995-12-richard.henderson@linaro.org/

Wherein I use the host off_t (which must be 64-bits).
(I'm pretty sure there's an older similar patch, but I couldn't find it.)


r~