[PATCH 0/1] MR5227: ntdll: Respect red zone in usr1_handler() on x64.

[Paul Gofman (＠gofman)]

Fixes a regression introduced by efd3d31082645fab83c6a4994705654edafa9163 ("ntdll: Don't copy xstate from / to syscall frame in usr1_handler().").

SysV x64 ABI assumes 128 byte red zone below stack pointer (for optimizing leaf functions by using the space below rsp saving some stack allocation instructions). I stomped on that red zone is used for real in win32u Unix lib leaf functions causing random crashes inside win32u syscalls when sigusr1 clobbers that zone.

[PATCH 1/1] ntdll: Respect red zone in usr1_handler() on x64.

[Paul Gofman]

From: Paul Gofman

Fixes a regression introduced by
efd3d31082645fab83c6a4994705654edafa9163.
---
 dlls/ntdll/unix/signal_x86_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dlls/ntdll/unix/signal_x86_64.c b/dlls/ntdll/unix/signal_x86_64.c
index fb1bca99f3d..d071120af85 100644
--- a/dlls/ntdll/unix/signal_x86_64.c
+++ b/dlls/ntdll/unix/signal_x86_64.c
@@ -2152,7 +2152,7 @@ static void usr1_handler( int signal, siginfo_t *siginfo, void *sigcontext )
         ULONG64 saved_compaction = 0;
         struct xcontext *context;

-        context = (struct xcontext *)(((ULONG_PTR)RSP_sig(ucontext) - sizeof(*context)) & ~15);
+        context = (struct xcontext *)(((ULONG_PTR)RSP_sig(ucontext) - 128 /* red zone */ - sizeof(*context)) & ~15);
         if ((char *)context < (char *)ntdll_get_thread_data()->kernel_stack)
         {
             ERR_(seh)( "kernel stack overflow.\n" );