From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 20 Aug 2013 16:05:16 +1000 From: Anton Blanchard To: benh@kernel.crashing.org, paulus@samba.org, mikey@neuling.org, amodra@gmail.com Subject: [PATCH] powerpc: Never handle VSX alignment exceptions from kernel Message-ID: <20130820160516.596a85a4@kryten> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Cc: linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , The VSX alignment handler needs to write out the existing VSX state to memory before operating on it (flush_vsx_to_thread()). If we take a VSX alignment exception in the kernel bad things will happen. It looks like we could write the kernel state out to the user process, or we could handle the kernel exception using data from the user process (depending if MSR_VSX is set or not). Worse still, if the code to read or write the VSX state causes an alignment exception, we will recurse forever. I ended up with hundreds of megabytes of kernel stack to look through as a result. Floating point and SPE code have similar issues but already include a user check. Add the same check to emulate_vsx(). Signed-off-by: Anton Blanchard --- Index: b/arch/powerpc/kernel/align.c =================================================================== --- a/arch/powerpc/kernel/align.c +++ b/arch/powerpc/kernel/align.c @@ -651,6 +651,10 @@ static int emulate_vsx(unsigned char __u int sw = 0; int i, j; + /* userland only */ + if (unlikely(!user_mode(regs))) + return 0; + flush_vsx_to_thread(current); if (reg < 32)