From: David Woodhouse <dwmw2@redhat.com>
Subject: [RHEL5] #220586 - Avoid kernel panic when taking altivec exceptions from userspace.
Date: Wed, 03 Jan 2007 18:52:41 +0000
Bugzilla: 220586
Message-Id: <1167850361.19205.15.camel@pmac.infradead.org>
Changelog: ppc64: Avoid panic when taking altivec exceptions from userspace.


When the CPU has altivec support but the kernel doesn't realise it --
because it's a new CPU not known in the PVR table and the firmware
doesn't announce the availability of altivec support, userspace can
panic the machine.

This is a bad thing.

The simple patch from upstream unconditionally delivers SIGILL if the
exception comes from userspace, rather than panicking.

commit 6c4841c2b6c32a134f9f36e5e08857138cc12b10
Author: Anton Blanchard <anton@samba.org>

    [POWERPC] Never panic when taking altivec exceptions from userspace
    
    At the moment we rely on a cpu feature bit or a firmware property to
    detect altivec. If we dont have either of these and the cpu does in fact
    support altivec we can cause a panic from userspace.
    
    It seems safer to always send a signal if we manage to get an 0xf20
    exception from userspace.
    
    Signed-off-by: Anton Blanchard <anton@samba.org>
    Signed-off-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index d9f10f2..5ed4c2c 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -900,14 +900,13 @@ void kernel_fp_unavailable_exception(struct pt_regs *regs)
 
 void altivec_unavailable_exception(struct pt_regs *regs)
 {
-#if !defined(CONFIG_ALTIVEC)
 	if (user_mode(regs)) {
 		/* A user program has executed an altivec instruction,
 		   but this kernel doesn't support altivec. */
 		_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
 		return;
 	}
-#endif
+
 	printk(KERN_EMERG "Unrecoverable VMX/Altivec Unavailable Exception "
 			"%lx at %lx\n", regs->trap, regs->nip);
 	die("Unrecoverable VMX/Altivec Unavailable Exception", regs, SIGABRT);

-- 
dwmw2