linux-user: Emulate /proc/self/maps under mmap_lock

If one thread modifies the mappings and another thread prints them,
a situation may occur that the printer thread sees a guest mapping
without a corresponding host mapping, leading to a crash in
open_self_maps_2().

Cc: qemu-stable@nongnu.org
Fixes: 7b7a3366e142 ("linux-user: Use walk_memory_regions for open_self_maps")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20241014203441.387560-1-iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
(cherry picked from commit bbd5630a75e70a0f1bcf04de74c94aa94a145628)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: context fix in linux-user/syscall.c due to missing v9.0.0-421-g59272469bd13
 "user: Use get_task_state() helper")

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 2edbd1ef15caf940842a9c1c8961d2ed051522ea..caa91c3b1dd3816a32c18ce50f73db6b1d3600af 100644 (file)
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8132,17 +8132,19 @@ static int open_self_maps_1(CPUArchState *env, int fd, bool smaps)
 {
     struct open_self_maps_data d = {
         .ts = env_cpu(env)->opaque,
-        .host_maps = read_self_maps(),
         .fd = fd,
         .smaps = smaps
     };
 
+    mmap_lock();
+    d.host_maps = read_self_maps();
     if (d.host_maps) {
         walk_memory_regions(&d, open_self_maps_2);
         free_self_maps(d.host_maps);
     } else {
         walk_memory_regions(&d, open_self_maps_3);
     }
+    mmap_unlock();
     return 0;
 }