[PATCH v4 08/10] loader: Relocate sigpage on conflict with reserved ranges in ARM.

[Jinoh Kang]

Today, the preloader makes no attempt to remap the sigpage when it
conflicts with reserved addresses.  If libc doesn't have its own signal
restorer, this results in inability to return from signal handlers.

Fix this by relocating sigpage to another address whenever possible.

Since this is a potentially risky change, this behaviour is hidden
behind the "WINEPRELOADREMAPSIGPAGE" environment variable.  To activate
the behaviour, the user needs to set
"WINEPRELOADREMAPSIGPAGE=on-conflict".  After sufficient testing has
been done via staging process, the new behaviour could be the default
and the environment variables removed.

Signed-off-by: Jinoh Kang <jinoh.kang.kr at gmail.com>
---

Notes:
    v1 -> v2: new patch
    
    v3 -> v4:
    - add documentation for remap_sigpage
    - fix indentation

 loader/preloader.c | 75 ++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 70 insertions(+), 5 deletions(-)

diff --git a/loader/preloader.c b/loader/preloader.c
index 52036dee554..70cefe576ac 100644
--- a/loader/preloader.c
+++ b/loader/preloader.c
@@ -252,9 +252,12 @@ struct linebuffer
  */
 enum vma_type_flags
 {
-    VMA_NORMAL = 0x01,
-    VMA_VDSO   = 0x02,
-    VMA_VVAR   = 0x04,
+    VMA_NORMAL  = 0x01,
+    VMA_VDSO    = 0x02,
+    VMA_VVAR    = 0x04,
+#ifdef __arm__
+    VMA_SIGPAGE = 0x08,
+#endif
 };
 
 struct vma_area
@@ -287,7 +290,10 @@ enum remap_policy
     REMAP_POLICY_SKIP = 2,
     LAST_REMAP_POLICY,
 
-    REMAP_POLICY_DEFAULT_VDSO = REMAP_POLICY_SKIP,
+    REMAP_POLICY_DEFAULT_VDSO    = REMAP_POLICY_SKIP,
+#ifdef __arm__
+    REMAP_POLICY_DEFAULT_SIGPAGE = REMAP_POLICY_SKIP,
+#endif
 };
 
 /*
@@ -1947,6 +1953,10 @@ static int parse_maps_line( struct vma_area *entry, const char *line )
             item.type_flags |= VMA_VDSO;
         else if (wld_strcmp(ptr, "[vvar]") == 0)
             item.type_flags |= VMA_VVAR;
+#ifdef __arm__
+        else if (wld_strcmp(ptr, "[sigpage]") == 0)
+            item.type_flags |= VMA_SIGPAGE;
+#endif
     }
 
     *entry = item;
@@ -2459,6 +2469,55 @@ remap_restore:
     return -1;
 }
 
+#ifdef __arm__
+/*
+ * remap_sigpage
+ *
+ * Perform sigpage remapping if it conflicts with one of the reserved address ranges.
+ *
+ * sigpage remapping shouldn't really be necessary, since modern libcs
+ * use their own signal restorer anyway.  But better be safe than sorry...
+ */
+static int remap_sigpage( struct vma_area_list *vma_list, struct preloader_state *state )
+{
+    int result;
+    unsigned long sigpage_start, sigpage_size, delta;
+    void *new_sigpage;
+
+    if (find_vma_envelope_range( vma_list, VMA_SIGPAGE,
+                                 &sigpage_start, &sigpage_size ) < 0) return 0;
+
+    result = check_remap_policy( state, "WINEPRELOADREMAPSIGPAGE",
+                                 REMAP_POLICY_DEFAULT_SIGPAGE,
+                                 sigpage_start, sigpage_size );
+    if (result <= 0) return result;
+
+    new_sigpage = wld_mmap( NULL, sigpage_size, PROT_NONE,
+                            MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0 );
+    if (new_sigpage == (void *)-1) return -1;
+
+    delta = (unsigned long)new_sigpage - sigpage_start;
+    if (remap_multiple_vmas( vma_list, delta, VMA_SIGPAGE, 0 ) < 0) goto remap_restore;
+
+    if (test_remap_successful( vma_list, state, sigpage_start, sigpage_size, delta ) < 0)
+    {
+        /* mapping restore done by test_remap_successful */
+        return -1;
+    }
+
+    /* Refresh VMA list */
+    free_vma_list( vma_list );
+    alloc_scan_vma( vma_list );
+    return 1;
+
+remap_restore:
+    if (remap_multiple_vmas( vma_list, delta, -1, 1 ) < 0)
+        fatal_error( "Cannot restore remapped VMAs\n" );
+
+    return -1;
+}
+#endif
+
 /*
  * map_reserve_preload_ranges
  *
@@ -2514,6 +2573,7 @@ void* wld_start( void **stack )
     struct wine_preload_info **wine_main_preload_info;
     struct preloader_state state = { 0 };
     struct vma_area_list vma_list = { NULL };
+    int remap_done;
 
     parse_stackargs( &state.s, *stack );
 
@@ -2546,7 +2606,12 @@ void* wld_start( void **stack )
     alloc_scan_vma( &vma_list );
     map_reserve_preload_ranges( &vma_list, &state.s );
 
-    if (remap_vdso( &vma_list, &state ) > 0) map_reserve_preload_ranges( &vma_list, &state.s );
+    remap_done = 0;
+    remap_done |= remap_vdso( &vma_list, &state ) > 0;
+#ifdef __arm__
+    remap_done |= remap_sigpage( &vma_list, &state ) > 0;
+#endif
+    if (remap_done) map_reserve_preload_ranges( &vma_list, &state.s );
 
     /* add an executable page at the top of the address space to defeat
      * broken no-exec protections that play with the code selector limit */
-- 
2.34.1