Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932449AbaJWSjx (ORCPT ); Thu, 23 Oct 2014 14:39:53 -0400 Received: from mail-pa0-f54.google.com ([209.85.220.54]:58355 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754564AbaJWSjw (ORCPT ); Thu, 23 Oct 2014 14:39:52 -0400 Message-ID: <54494B74.2080504@amacapital.net> Date: Thu, 23 Oct 2014 11:39:48 -0700 From: Andy Lutomirski User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.1 MIME-Version: 1.0 To: Eric Paris , rgb@redhat.com CC: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, linux-audit@redhat.com Subject: Re: [PATCH] i386/audit: stop scribbling on the stack frame References: <1414037043-30647-1-git-send-email-eparis@redhat.com> In-Reply-To: <1414037043-30647-1-git-send-email-eparis@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/22/2014 09:04 PM, Eric Paris 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. > > 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. > > Signed-off-by: Eric Paris > 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 > --- > 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 f9e3fab..fb01d22 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_EAX(%esp), %eax already set, syscall number: 1st arg to audit */ > + movl PT_EBX(%esp), %edx /* ebx/a0: 2nd arg to audit */ > + /* movl PT_ECX(%esp), %ecx already set, a1: 3nd arg to audit */ > + pushl_cfi PT_ESI(%esp) /* a3: 5th arg */ > + pushl_cfi PT_EDX+4(%esp) /* a2: 4th arg */ > 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 > > This looks reasonably likely to be correct, but this code is complicated and now ever slower. How hard would it be to just delete it and replace it with a straightforward two-phase trace invocation a la x86_64? --Andy -- 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/