Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751847AbaJ0Ria (ORCPT ); Mon, 27 Oct 2014 13:38:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35651 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751596AbaJ0Ri2 (ORCPT ); Mon, 27 Oct 2014 13:38:28 -0400 Date: Mon, 27 Oct 2014 13:38:15 -0400 From: Richard Guy Briggs To: Eric Paris 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 Subject: Re: [PATCH] i386/audit: stop scribbling on the stack frame Message-ID: <20141027173815.GA15532@madcap2.tricolour.ca> References: <1414037043-30647-1-git-send-email-eparis@redhat.com> <20141027023457.GY15532@madcap2.tricolour.ca> <1414418157.24347.1.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1414418157.24347.1.camel@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14/10/27, Eric Paris wrote: > 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. I was just more surprised that you didn't use the assumptions and approach of the original code before I botched it, which simply re-used values in registers that were already there, rather than fetching them from the pt_regs struct on the stack and adjusting the reference with an offset on the fly as you're pushing items onto the stack. > -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 > > - 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/