Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755384Ab0BFKWS (ORCPT ); Sat, 6 Feb 2010 05:22:18 -0500 Received: from ozlabs.org ([203.10.76.45]:58839 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754138Ab0BFKWR (ORCPT ); Sat, 6 Feb 2010 05:22:17 -0500 From: Michael Neuling To: Anton Blanchard cc: stable@kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Serge Hallyn , WANG Cong , Paul Mackerras , benh@kernel.crashing.org, miltonm@bga.com, aeb@cwi.nl Subject: Re: Stack size protection broken on ppc64 In-reply-to: <20100206042038.GB32246@kryten> References: <3984.1265416993@neuling.org> <20100206042038.GB32246@kryten> Comments: In-reply-to Anton Blanchard message dated "Sat, 06 Feb 2010 15:20:38 +1100." X-Mailer: MH-E 8.2; nmh 1.3; GNU Emacs 23.1.1 Date: Sat, 06 Feb 2010 21:22:12 +1100 Message-ID: <10125.1265451732@neuling.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3179 Lines: 89 > > On recent ppc64 kernels, limiting the stack (using 'ulimit -s blah') is > > now more restrictive than it was before. On 2.6.31 with 4k pages I > > could run 'ulimit -s 16; /usr/bin/test' without a problem. Now with > > mainline, even 'ulimit -s 64; /usr/bin/test' gets killed. > > > > Using 64k pages is even worse. I can't even run '/bin/ls' with a 1MB > > stack (ulimit -s 1024; /bin/ls). Hence, it seems new kernels are too > > restrictive, rather than the old kernels being too liberal. > > It looks like this is causing it: > > #define EXTRA_STACK_VM_PAGES 20 /* random */ > > ... > > #ifdef CONFIG_STACK_GROWSUP > stack_base = vma->vm_end + EXTRA_STACK_VM_PAGES * PAGE_SIZE; > #else > stack_base = vma->vm_start - EXTRA_STACK_VM_PAGES * PAGE_SIZE; > #endif > > Which got added back in 2005 in a memory overcommit patch. It only took 5 > years for us to go back and review that random setting :) > > The comment from Andries explains the purpose: > > (1) It reserves a reasonable amount of virtual stack space (amount > randomly chosen, no guarantees given) when the process is started, so > that the common utilities will not be killed by segfault on stack > extension. > > This explains why 64kB is much worse. The extra stack reserve should be in kB > and we also need to be careful not to ask for more than our rlimit. Cool, thanks. The following is based on this and fixes the problem for me on PPC64 ie. the !CONFIG_STACK_GROWSUP case. Mikey [PATCH] Restrict stack space reservation to rlimit When reserving stack space for a new process, make sure we're not attempting to allocate more than rlimit allows. Also, reserve the same stack size independent of page size. This fixes a bug unmasked by fc63cf237078c86214abcb2ee9926d8ad289da9b Signed-off-by: Michael Neuling Cc: Anton Blanchard Cc: stable@kernel.org --- fs/exec.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) Index: clone1/fs/exec.c =================================================================== --- clone1.orig/fs/exec.c +++ clone1/fs/exec.c @@ -554,7 +554,7 @@ static int shift_arg_pages(struct vm_are return 0; } -#define EXTRA_STACK_VM_PAGES 20 /* random */ +#define EXTRA_STACK_VM_SIZE 81920UL /* randomly 20 4K pages */ /* * Finalizes the stack vm_area_struct. The flags and permissions are updated, @@ -627,10 +627,13 @@ int setup_arg_pages(struct linux_binprm goto out_unlock; } + stack_base = min(EXTRA_STACK_VM_SIZE, + current->signal->rlim[RLIMIT_STACK].rlim_cur) - + PAGE_SIZE; #ifdef CONFIG_STACK_GROWSUP - stack_base = vma->vm_end + EXTRA_STACK_VM_PAGES * PAGE_SIZE; + stack_base = vma->vm_end + stack_base; #else - stack_base = vma->vm_start - EXTRA_STACK_VM_PAGES * PAGE_SIZE; + stack_base = vma->vm_start - stack_base; #endif ret = expand_stack(vma, stack_base); if (ret) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/