Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755197AbXKGPtk (ORCPT ); Wed, 7 Nov 2007 10:49:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753578AbXKGPtd (ORCPT ); Wed, 7 Nov 2007 10:49:33 -0500 Received: from saraswathi.solana.com ([198.99.130.12]:59219 "EHLO saraswathi.solana.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750830AbXKGPtc (ORCPT ); Wed, 7 Nov 2007 10:49:32 -0500 Date: Wed, 7 Nov 2007 10:48:39 -0500 From: Jeff Dike To: Andrew Morton , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, Chuck Ebbert <76306.1226@compuserve.com>, Roland McGrath Cc: LKML Subject: [PATCH] x86 - 32-bit ptrace emulation mishandles 6th arg Message-ID: <20071107154839.GA5981@c2.user-mode-linux.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3099 Lines: 86 From: Chuck Ebbert <76306.1226@compuserve.com> [ jdike - Pushing Chuck's patch - see http://lkml.org/lkml/2005/9/16/261 for some history and a test program. UML is also broken without this patch - its processes get SIGBUS from the corrupt 6th argument to mmap being interpretted as a file offset ] When the 32-bit vDSO is used to make a system call, the %ebp register for the 6th syscall arg has to be loaded from the user stack (where it's pushed by the vDSO user code). The native i386 kernel always does this before stopping for syscall tracing, so %ebp can be seen and modified via ptrace to access the 6th syscall argument. The x86-64 kernel fails to do this, presenting the stack address to ptrace instead. This makes the %rbp value seen by 64-bit ptrace of a 32-bit process, and the %ebp value seen by a 32-bit caller of ptrace, both differ from the native i386 behavior. This patch fixes the problem by putting the word loaded from the user stack into %rbp before calling syscall_trace_enter, and reloading the 6th syscall argument from there afterwards (so ptrace can change it). This makes the behavior match that of i386 kernels. Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com> Signed-off-by: Jeff Dike Original-Patch-By: Roland McGrath --- arch/x86_64/ia32/ia32entry.S | 19 ++++++------------- 1 file changed, 6 insertions(+), 13 deletions(-) diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S index 18b2318..df588f0 100644 --- a/arch/x86/ia32/ia32entry.S +++ b/arch/x86/ia32/ia32entry.S @@ -159,20 +159,16 @@ sysenter_do_call: sysenter_tracesys: CFI_RESTORE_STATE + xchgl %r9d,%ebp SAVE_REST CLEAR_RREGS + movq %r9,R9(%rsp) movq $-ENOSYS,RAX(%rsp) /* really needed? */ movq %rsp,%rdi /* &pt_regs -> arg1 */ call syscall_trace_enter LOAD_ARGS32 ARGOFFSET /* reload args from stack in case ptrace changed it */ RESTORE_REST - movl %ebp, %ebp - /* no need to do an access_ok check here because rbp has been - 32bit zero extended */ -1: movl (%rbp),%r9d - .section __ex_table,"a" - .quad 1b,ia32_badarg - .previous + xchgl %ebp,%r9d jmp sysenter_do_call CFI_ENDPROC ENDPROC(ia32_sysenter_target) @@ -262,20 +258,17 @@ cstar_do_call: cstar_tracesys: CFI_RESTORE_STATE + xchgl %r9d,%ebp SAVE_REST CLEAR_RREGS + movq %r9,R9(%rsp) movq $-ENOSYS,RAX(%rsp) /* really needed? */ movq %rsp,%rdi /* &pt_regs -> arg1 */ call syscall_trace_enter LOAD_ARGS32 ARGOFFSET /* reload args from stack in case ptrace changed it */ RESTORE_REST + xchgl %ebp,%r9d movl RSP-ARGOFFSET(%rsp), %r8d - /* no need to do an access_ok check here because r8 has been - 32bit zero extended */ -1: movl (%r8),%r9d - .section __ex_table,"a" - .quad 1b,ia32_badarg - .previous jmp cstar_do_call END(ia32_cstar_target) - 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/