Alexandre Julliard : ntdll: Don't use virtual_uninterrupted_read_memory() for invalid %gs check.

[Alexandre Julliard]

Module: wine
Branch: master
Commit: 5f10545b199ce44de7f91d719131767396e320c7
URL:    https://source.winehq.org/git/wine.git/?a=commit;h=5f10545b199ce44de7f91d719131767396e320c7

Author: Alexandre Julliard <julliard at winehq.org>
Date:   Tue Sep 17 16:02:55 2019 +0200

ntdll: Don't use virtual_uninterrupted_read_memory() for invalid %gs check.

It doesn't work for code in system libraries. This is a partial revert
of 58139dcb125390b9a2bcd79869d571337d8ab3d8.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=47769
Signed-off-by: Alexandre Julliard <julliard at winehq.org>

---

 dlls/ntdll/signal_i386.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/dlls/ntdll/signal_i386.c b/dlls/ntdll/signal_i386.c
index 8d1c591504..f15b327624 100644
--- a/dlls/ntdll/signal_i386.c
+++ b/dlls/ntdll/signal_i386.c
@@ -1595,17 +1595,16 @@ static inline DWORD is_privileged_instr( CONTEXT *context )
  */
 static inline BOOL check_invalid_gs( ucontext_t *sigcontext, CONTEXT *context )
 {
-    BYTE instr[14];
-    unsigned int i, len;
+    unsigned int prefix_count = 0;
+    const BYTE *instr = (BYTE *)context->Eip;
     WORD system_gs = x86_thread_data()->gs;
 
     if (context->SegGs == system_gs) return FALSE;
     if (!wine_ldt_is_system( context->SegCs )) return FALSE;
     /* only handle faults in system libraries */
-    if (virtual_is_valid_code_address( (BYTE *)context->Eip, 1 )) return FALSE;
+    if (virtual_is_valid_code_address( instr, 1 )) return FALSE;
 
-    len = virtual_uninterrupted_read_memory( (BYTE *)context->Eip, instr, sizeof(instr) );
-    for (i = 0; i < len; i++) switch (instr[i])
+    for (;;) switch(*instr)
     {
     /* instruction prefixes */
     case 0x2e:  /* %cs: */
@@ -1618,6 +1617,8 @@ static inline BOOL check_invalid_gs( ucontext_t *sigcontext, CONTEXT *context )
     case 0xf0:  /* lock */
     case 0xf2:  /* repne */
     case 0xf3:  /* repe */
+        if (++prefix_count >= 15) return FALSE;
+        instr++;
         continue;
     case 0x65:  /* %gs: */
         TRACE( "%04x/%04x at %p, fixing up\n", context->SegGs, system_gs, instr );
@@ -1628,7 +1629,6 @@ static inline BOOL check_invalid_gs( ucontext_t *sigcontext, CONTEXT *context )
     default:
         return FALSE;
     }
-    return FALSE;
 }