[PATCH] Clear TLS on execve

[PATCH] Clear TLS on execve

[Luca Barbieri]

[-- Attachment #1: Type: text/plain, Size: 1008 bytes --]

This trivial patch causes the TLS to be cleared on execve (code is in flush_thread).
This is necessary to avoid ESRCH errors when set_thread_area is asked
to choose a free TLS entry after several nested execve's.

The LDT also has a similar problem, but it is less serious because the
LDT code doesn't scan for free entries. I'll probably send a patch to
fix this too, unless there is something important relying on this behavior.

diff --exclude-from=/home/ldb/src/linux-exclude -urNdp linux-2.5.45/arch/i386/kernel/process.c linux-2.5.45_ldb/arch/i386/kernel/process.c
--- linux-2.5.45/arch/i386/kernel/process.c	2002-10-12 06:21:02.000000000 +0200
+++ linux-2.5.45_ldb/arch/i386/kernel/process.c	2002-10-31 14:23:18.000000000 +0100
@@ -247,6 +247,7 @@ void flush_thread(void)
 	struct task_struct *tsk = current;
 
 	memset(tsk->thread.debugreg, 0, sizeof(unsigned long)*8);
+	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));	
 	/*
 	 * Forget coprocessor state..
 	 */

[-- Attachment #2: Type: application/pgp-signature, Size: 189 bytes --]

Re: [PATCH] Clear TLS on execve

[Jamie Lokier]

Luca Barbieri wrote:
> This trivial patch causes the TLS to be cleared on execve (code is
> in flush_thread).  This is necessary to avoid ESRCH errors when
> set_thread_area is asked to choose a free TLS entry after several
> nested execve's.

Ouch!

> The LDT also has a similar problem, but it is less serious because the
> LDT code doesn't scan for free entries. I'll probably send a patch to
> fix this too, unless there is something important relying on this behavior.

Ouch again!  Does the LDT really not get released on execve?  I am
using threading code which _does_ scan for free entries in the LDT -
using the lar instruction.  I'd never stumbled across this, though.
I'll be glad of your patch.

-- Jamie