Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753069AbaJ0N4N (ORCPT ); Mon, 27 Oct 2014 09:56:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34779 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752655AbaJ0N4L (ORCPT ); Mon, 27 Oct 2014 09:56:11 -0400 Message-ID: <1414418157.24347.1.camel@redhat.com> Subject: Re: [PATCH] i386/audit: stop scribbling on the stack frame From: Eric Paris To: Richard Guy Briggs Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, przanoni@gmail.com, mingo@kernel.org, hpa@linux.intel.com, hpa@zytor.com, linux-tip-commits@vger.kernel.org, linux-audit@redhat.com Date: Mon, 27 Oct 2014 09:55:57 -0400 In-Reply-To: <20141027023457.GY15532@madcap2.tricolour.ca> References: <1414037043-30647-1-git-send-email-eparis@redhat.com> <20141027023457.GY15532@madcap2.tricolour.ca> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org My patch was already committed to the -tip urgent branch. I believe any optimization should be based on that branch, Richard. If you are trying to wrangle every bit of speed out of this, should you push %esi; push %edi; CFI_ADJUST_CFA_OFFSET 8 call __audit_syscall_entry pop; pop; CFI_ADJUST_CFA_OFFSET -8 Instead of using the pushl_cfi and popl_cfi macros? I wrote my patch to be obviously correct, but agree there are certainly some speedups possible. -Eric On Sun, 2014-10-26 at 22:34 -0400, Richard Guy Briggs wrote: > git commit b4f0d3755c5e9cc86292d5fd78261903b4f23d4a was very very dumb. > It was writing over %esp/pt_regs semi-randomly on i686 with the expected > "system can't boot" results. As noted in: > > https://bugs.freedesktop.org/show_bug.cgi?id=85277 > > This patch stops fscking with pt_regs. Instead it sets up the registers > for the call to __audit_syscall_entry in the most obvious conceivable > way. It then does just a tiny tiny touch of magic. We need to get what > started in PT_EDX into 0(%esp) and PT_ESI into 4(%esp). This is as easy > as a pair of pushes using the values still in those registers. > > After the call to __audit_syscall_entry all we need to do is get that > now useless junk off the stack (pair of pops) and reload %eax with the > original syscall so other stuff can keep going about it's business. > > Reported-by: Paulo Zanoni > Signed-off-by: Eric Paris > Signed-off-by: Richard Guy Briggs > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: "H. Peter Anvin" > Cc: x86@kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: linux-audit@redhat.com > > --- > On 14/10/25, Thomas Gleixner wrote: > > Why are we grabbing that from the stack? AFAICT all arguments are in > > the registers still. > > Right, re-arranging the instructions slightly to avoid overwriting %edx > with %ebx before needing it to push onto the stack, how does this look? > > arch/x86/kernel/entry_32.S | 15 +++++++-------- > 1 file changed, 7 insertions(+), 8 deletions(-) > > diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S > index b553ed8..344b63f 100644 > --- a/arch/x86/kernel/entry_32.S > +++ b/arch/x86/kernel/entry_32.S > @@ -447,15 +447,14 @@ sysenter_exit: > sysenter_audit: > testl $(_TIF_WORK_SYSCALL_ENTRY & ~_TIF_SYSCALL_AUDIT),TI_flags(%ebp) > jnz syscall_trace_entry > - addl $4,%esp > - CFI_ADJUST_CFA_OFFSET -4 > - movl %esi,4(%esp) /* 5th arg: 4th syscall arg */ > - movl %edx,(%esp) /* 4th arg: 3rd syscall arg */ > - /* %ecx already in %ecx 3rd arg: 2nd syscall arg */ > - movl %ebx,%edx /* 2nd arg: 1st syscall arg */ > - /* %eax already in %eax 1st arg: syscall number */ > + /* movl PT_ECX(%esp), %ecx already set, a1: 3nd arg to audit */ > + /* movl PT_EAX(%esp), %eax already set, syscall number: 1st arg to audit */ > + pushl_cfi %esi /* a3: 5th arg */ > + pushl_cfi %edx /* a2: 4th arg */ > + movl %ebx, %edx /* ebx/a0: 2nd arg to audit */ > call __audit_syscall_entry > - pushl_cfi %ebx > + popl_cfi %ecx /* get that remapped edx off the stack */ > + popl_cfi %ecx /* get that remapped esi off the stack */ > movl PT_EAX(%esp),%eax /* reload syscall number */ > jmp sysenter_do_call > > > - RGB > > -- > Richard Guy Briggs > Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat > Remote, Ottawa, Canada > Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545 -- 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/