Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759578AbbFCM41 (ORCPT ); Wed, 3 Jun 2015 08:56:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58755 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754424AbbFCM4Q (ORCPT ); Wed, 3 Jun 2015 08:56:16 -0400 From: Denys Vlasenko To: Ingo Molnar Cc: Denys Vlasenko , Linus Torvalds , Steven Rostedt , Borislav Petkov , "H. Peter Anvin" , Andy Lutomirski , Oleg Nesterov , Frederic Weisbecker , Alexei Starovoitov , Will Drewry , Kees Cook , x86@kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] x86/asm/entry/32: Do not use r9 in SYSCALL32 entry point Date: Wed, 3 Jun 2015 14:56:09 +0200 Message-Id: <1433336169-18964-1-git-send-email-dvlasenk@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4388 Lines: 140 SYSENTER and SYSCALL 32-bit entry points differ in handling of arg2 and arg6. SYSENTER: * ecx arg2 * ebp user stack * 0(%ebp) arg6 SYSCALL: * ebp arg2 * esp user stack * 0(%esp) arg6 Sysenter code loads 0(%ebp) to %ebp right away. (This destroys %ebp. It means we do not preserve it on return. It's not causing problems since userspace VDSO code does not depend on it, and SYSENTER insn can't be sanely used outside of VDSO). Syscall code loads 0(%ebp) to %r9. This allows to eliminate one MOV insn (r9 is a register where arg6 should be for 64-bit ABI), but on audit/ptrace code paths this requires juggling of r9 and ebp: (1) ptrace expects arg6 to be in pt_regs->bp; (2) r9 is callee-clobbered register and needs to be saved/restored around calls to C functions. This patch changes syscall code to load 0(%ebp) to %ebp, making it more similar to sysenter code. It's a bit smaller: text data bss dec hex filename 1407 0 0 1407 57f ia32entry.o.before 1391 0 0 1391 56f ia32entry.o To preserve ABI compat, we restore ebp on exit. Run-tested. Signed-off-by: Denys Vlasenko CC: Linus Torvalds CC: Steven Rostedt CC: Ingo Molnar CC: Borislav Petkov CC: "H. Peter Anvin" CC: Andy Lutomirski CC: Oleg Nesterov CC: Frederic Weisbecker CC: Alexei Starovoitov CC: Will Drewry CC: Kees Cook CC: x86@kernel.org CC: linux-kernel@vger.kernel.org --- This patch is on top of: x86/asm/entry/32: Simplify zeroing of pt_regs->r8..r11 on int80 code path x86/asm/entry/32: Open-code CLEAR_RREGS. No code changes. x86/asm/entry/32: Open-code LOAD_ARGS32. No code changes. arch/x86/ia32/ia32entry.S | 19 ++++++++----------- 1 file changed, 8 insertions(+), 11 deletions(-) diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S index 0ff676a..6f29f1f 100644 --- a/arch/x86/ia32/ia32entry.S +++ b/arch/x86/ia32/ia32entry.S @@ -327,7 +327,7 @@ ENTRY(ia32_cstar_target) * 32bit zero extended */ ASM_STAC -1: movl (%r8),%r9d +1: movl (%r8),%ebp _ASM_EXTABLE(1b,ia32_badarg) ASM_CLAC orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS) @@ -337,7 +337,7 @@ ENTRY(ia32_cstar_target) cstar_do_call: /* 32bit syscall -> 64bit C ABI argument conversion */ movl %edi,%r8d /* arg5 */ - /* r9 already loaded */ /* arg6 */ + movl %ebp,%r9d /* arg6 */ xchg %ecx,%esi /* rsi:arg2, rcx:arg4 */ movl %ebx,%edi /* arg1 */ movl %edx,%edx /* arg3 (zero extension) */ @@ -353,6 +353,7 @@ cstar_dispatch: jnz sysretl_audit sysretl_from_sys_call: andl $~TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS) + movl RCX(%rsp), %ebp RESTORE_RSI_RDI_RDX movl RIP(%rsp),%ecx movl EFLAGS(%rsp),%r11d @@ -379,9 +380,8 @@ sysretl_from_sys_call: #ifdef CONFIG_AUDITSYSCALL cstar_auditsys: - movl %r9d,R9(%rsp) /* register to be clobbered by call */ auditsys_entry_common - movl R9(%rsp),%r9d /* reload 6th syscall arg */ + movl %ebp, %r9d /* reload 6th syscall arg */ jmp cstar_dispatch sysretl_audit: @@ -393,16 +393,14 @@ cstar_tracesys: testl $(_TIF_WORK_SYSCALL_ENTRY & ~_TIF_SYSCALL_AUDIT), ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS) jz cstar_auditsys #endif - xchgl %r9d,%ebp SAVE_EXTRA_REGS xorl %eax, %eax movq %rax, R11(%rsp) movq %rax, R10(%rsp) - movq %r9, R9(%rsp) + movq %rax, R9(%rsp) movq %rax, R8(%rsp) - movq %rsp,%rdi /* &pt_regs -> arg1 */ - call syscall_trace_enter - movl R9(%rsp),%r9d + movq %rsp, %rdi /* &pt_regs -> arg1 */ + call syscall_trace_enter /* * Reload arg registers from stack in case ptrace changed them. * Don't reload %eax because syscall_trace_enter() returned @@ -416,8 +414,7 @@ cstar_tracesys: movl RDI(%rsp), %edi movl %eax, %eax /* zero extension */ RESTORE_EXTRA_REGS - xchgl %ebp,%r9d - jmp cstar_do_call + jmp cstar_do_call END(ia32_cstar_target) ia32_badarg: -- 1.8.1.4 -- 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/