Re: [PATCH] ntdll: Catch page fault in RtlWow64EnableFsRedirectionEx

[Nikolay Sivov]

On 04.08.2016 20:05, Matt Robinson wrote:
> Previously, RtlWow64EnableFsRedirectionEx only returned
> STATUS_NOT_IMPLEMENTED if the old_value pointer started with 0x0000, and
> would cause an unhandled page fault if an invalid handle not starting
> with 0x00 was passed.  However, Windows seems to catch page faults when
> accessing old_value and returns STATUS_ACCESS_VIOLATION.
>
> This adds a test to confirm the behaviour and then wraps the access to
> old_value in an exception handler.
>
> Fixes https://bugs.winehq.org/show_bug.cgi?id=41066
>
> Signed-off-by: Matt Robinson <git(a)nerdoftheherd.com>
> ---
>  dlls/ntdll/directory.c       | 12 +++++++++++-
>  dlls/ntdll/tests/directory.c |  2 ++
>  2 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/dlls/ntdll/directory.c b/dlls/ntdll/directory.c
> index 4a34475..13df0d1 100644
> --- a/dlls/ntdll/directory.c
> +++ b/dlls/ntdll/directory.c
> @@ -106,6 +106,7 @@
>  #include "wine/list.h"
>  #include "wine/library.h"
>  #include "wine/debug.h"
> +#include "wine/exception.h"
>
> WINE_DEFAULT_DEBUG_CHANNEL(file);
>
> @@ -2998,7 +2999,16 @@ NTSTATUS WINAPI RtlWow64EnableFsRedirectionEx( ULONG disable, ULONG *old_value )
>      if (!is_wow64) return STATUS_NOT_IMPLEMENTED;
>      if (((ULONG_PTR)old_value >> 16) == 0) return STATUS_ACCESS_VIOLATION;

Looks like you can remove this old pointer check now.
> -    *old_value = !ntdll_get_thread_data()->wow64_redir;
> +    __TRY
> +    {
> +        *old_value = !ntdll_get_thread_data()->wow64_redir;
> +    }
> +    __EXCEPT_PAGE_FAULT
> +    {
> +        return STATUS_ACCESS_VIOLATION;
> +    }
> +    __ENDTRY
> +
>      ntdll_get_thread_data()->wow64_redir = !disable;
>      return STATUS_SUCCESS;
>  }