[Bug 37669] Resetting a write watch can cause memory access violation in kernel

[wine-bugs at winehq.org]

https://bugs.winehq.org/show_bug.cgi?id=37669

--- Comment #17 from Dmitry Timoshkov <dmitry at baikal.ru> ---
(In reply to Dmitry Timoshkov from comment #16)
> In order to solve this either apc callback should avoid generating
> exceptions,
> or it should be executed on win32 stack instead, perhaps wine_call_on_stack
> is the way to achieve that. Avoiding generating exceptions seems unfeasible
> to me, VirtualQuery() doesn't provide a way to detect write watchable memory,
> and I don't see another way to determine why recvmsg has returned EFAULT.

There is an obvious way to avoid generating exceptions and detecting a write
watchable memory region - GetWriteWatch. But the apc callback can't avoid
generating exceptions (by calling IsBadWritePtr) when recvmsg() returns
EFAULT because that's the only way for ntdll to make the buffer writable
before calling recvmsg() again.

So the Sebastian's patch can't work for asynchronous winsock recv() calls
without allowing exception handlers (at least inside of ntdll) work on
a signal stack, but that's a serious architectural violation of current
design of signal/SEH handling in wine.

I'll attach a test application which demonstrates both the current problem
with unexpected EFAULT return from asynchronous WSARecv(), and the receiver
thread dying due to an exception on signal stack with Sebastian's patch.

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