[glibc] hurd: Fix using altstack while in an RPC call to be aborted

[Samuel Thibault <sthibaul@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=e46efff89550a8e693a3362976f85070762c5cb8

commit e46efff89550a8e693a3362976f85070762c5cb8
Author: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date:   Wed Dec 11 00:23:00 2019 +0100

    hurd: Fix using altstack while in an RPC call to be aborted
    
    * sysdeps/mach/hurd/i386/trampoline.c (_hurd_setup_sighandler): Always check
    for interrupted code being with esp pointing at mach_msg arguments, even
    when using an altstack. If we need to abort the RPC we will need
    this.

Diff:
---
 sysdeps/mach/hurd/i386/trampoline.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/sysdeps/mach/hurd/i386/trampoline.c b/sysdeps/mach/hurd/i386/trampoline.c
index a6928a6..0c5d5a1 100644
--- a/sysdeps/mach/hurd/i386/trampoline.c
+++ b/sysdeps/mach/hurd/i386/trampoline.c
@@ -74,12 +74,6 @@ _hurd_setup_sighandler (struct hurd_sigstate *ss, __sighandler_t handler,
      interrupted RPC frame.  */
   state->basic.esp = state->basic.uesp;
 
-  if ((ss->actions[signo].sa_flags & SA_ONSTACK)
-      && !(ss->sigaltstack.ss_flags & (SS_DISABLE|SS_ONSTACK)))
-    {
-      sigsp = ss->sigaltstack.ss_sp + ss->sigaltstack.ss_size;
-      ss->sigaltstack.ss_flags |= SS_ONSTACK;
-    }
   /* This code has intimate knowledge of the special mach_msg system call
      done in intr-msg.c; that code does (see intr-msg.h):
 					movl %esp, %ecx
@@ -91,13 +85,20 @@ _hurd_setup_sighandler (struct hurd_sigstate *ss, __sighandler_t handler,
      We must check for the window during which %esp points at the
      mach_msg arguments.  The space below until %ecx is used by
      the _hurd_intr_rpc_mach_msg frame, and must not be clobbered.  */
-  else if (state->basic.eip >= (int) &_hurd_intr_rpc_msg_cx_sp
-	   && state->basic.eip < (int) &_hurd_intr_rpc_msg_sp_restored)
-    /* The SP now points at the mach_msg args, but there is more stack
-       space used below it.  The real SP is saved in %ecx; we must push the
-       new frame below there, and restore that value as the SP on
-       sigreturn.  */
-    sigsp = (char *) (state->basic.uesp = state->basic.ecx);
+  if (state->basic.eip >= (int) &_hurd_intr_rpc_msg_cx_sp
+      && state->basic.eip < (int) &_hurd_intr_rpc_msg_sp_restored)
+  /* The SP now points at the mach_msg args, but there is more stack
+     space used below it.  The real SP is saved in %ecx; we must push the
+     new frame below there (if not on the altstack), and restore that value as
+     the SP on sigreturn.  */
+    state->basic.uesp = state->basic.ecx;
+
+  if ((ss->actions[signo].sa_flags & SA_ONSTACK)
+      && !(ss->sigaltstack.ss_flags & (SS_DISABLE|SS_ONSTACK)))
+    {
+      sigsp = ss->sigaltstack.ss_sp + ss->sigaltstack.ss_size;
+      ss->sigaltstack.ss_flags |= SS_ONSTACK;
+    }
   else
     sigsp = (char *) state->basic.uesp;