From: Gerd Knorr <kraxel@bytesex.org>
Message-ID: <20040517172111.GA12321@bytesex.org>
Mime-Version: 1.0
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Content-Disposition: inline
Subject: [uml-devel] [patch] fix fault handling
Sender: user-mode-linux-devel-admin@lists.sourceforge.net
Errors-To: user-mode-linux-devel-admin@lists.sourceforge.net
Date: Mon, 17 May 2004 19:21:11 +0200
To: Jeff Dike <jdike@addtoit.com>, uml devel <user-mode-linux-devel@lists.sourceforge.net>

  Hi,

skas has a design bug: PTRACE_FAULTINFO doesn't pass enougth
informations.  Specifically the trap_no is missing, so you
don't know for sure whenever the SIGSEGV was a page fault or
a general protection fault.  I think that should be fixed in
skas4 (where we'll break backward compatibility anyway).

For the time being I've tried to fix that with the patch below,
which makes the uml kernel pass through general protection SEGV
to the app and seems to have no ill side effects.

  Gerd

--- linux-2.6.5/arch/um/kernel/skas/process.c.segv	2004-05-14 18:40:36.155621129 +0200
+++ linux-2.6.5/arch/um/kernel/skas/process.c	2004-05-14 19:49:00.762159068 +0200
@@ -54,6 +54,17 @@
 		panic("handle_segv - PTRACE_FAULTINFO failed, errno = %d\n",
 		      errno);
 
+	if (!(fault.is_write & 4)) {
+		/*
+		    kernel fault -- likely that was general
+ 		    protection fault (trap_no = 13), not a
+		    page fault (trap_no = 14).  But we don't
+		    know for sure as PTRACE_FAULTINFO doesn't
+		    tell us :-/
+		*/
+		bad_segv(fault.addr, 0, fault.is_write);
+		return;
+	}
 	segv(fault.addr, 0, FAULT_WRITE(fault.is_write), 1, NULL);
 }
 

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