From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751521AbdJTMaS (ORCPT ); Fri, 20 Oct 2017 08:30:18 -0400 Received: from terminus.zytor.com ([65.50.211.136]:57835 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751244AbdJTMaR (ORCPT ); Fri, 20 Oct 2017 08:30:17 -0400 Date: Fri, 20 Oct 2017 05:25:45 -0700 From: tip-bot for Dave Hansen Message-ID: Cc: dave.hansen@linux.intel.com, mingo@kernel.org, torvalds@linux-foundation.org, peterz@infradead.org, linux-kernel@vger.kernel.org, brgerst@gmail.com, luto@kernel.org, tglx@linutronix.de, hpa@zytor.com Reply-To: dave.hansen@linux.intel.com, peterz@infradead.org, torvalds@linux-foundation.org, mingo@kernel.org, brgerst@gmail.com, linux-kernel@vger.kernel.org, luto@kernel.org, tglx@linutronix.de, hpa@zytor.com In-Reply-To: <20171018172107.1A79C532@viggo.jf.intel.com> References: <20171018172107.1A79C532@viggo.jf.intel.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/asm] x86/entry: Use SYSCALL_DEFINE() macros for sys_modify_ldt() Git-Commit-ID: da20ab35180780e4a6eadc804544f1fa967f3567 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: da20ab35180780e4a6eadc804544f1fa967f3567 Gitweb: https://git.kernel.org/tip/da20ab35180780e4a6eadc804544f1fa967f3567 Author: Dave Hansen AuthorDate: Wed, 18 Oct 2017 10:21:07 -0700 Committer: Ingo Molnar CommitDate: Fri, 20 Oct 2017 10:37:33 +0200 x86/entry: Use SYSCALL_DEFINE() macros for sys_modify_ldt() We do not have tracepoints for sys_modify_ldt() because we define it directly instead of using the normal SYSCALL_DEFINEx() macros. However, there is a reason sys_modify_ldt() does not use the macros: it has an 'int' return type instead of 'unsigned long'. This is a bug, but it's a bug cemented in the ABI. What does this mean? If we return -EINVAL from a function that returns 'int', we have 0x00000000ffffffea in %rax. But, if we return -EINVAL from a function returning 'unsigned long', we end up with 0xffffffffffffffea in %rax, which is wrong. To work around this and maintain the 'int' behavior while using the SYSCALL_DEFINEx() macros, so we add a cast to 'unsigned int' in both implementations of sys_modify_ldt(). Signed-off-by: Dave Hansen Reviewed-by: Andy Lutomirski Reviewed-by: Brian Gerst Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20171018172107.1A79C532@viggo.jf.intel.com Signed-off-by: Ingo Molnar --- arch/x86/include/asm/syscalls.h | 2 +- arch/x86/kernel/ldt.c | 16 +++++++++++++--- arch/x86/um/ldt.c | 7 +++++-- 3 files changed, 19 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/syscalls.h b/arch/x86/include/asm/syscalls.h index 91dfcaf..bad25bb 100644 --- a/arch/x86/include/asm/syscalls.h +++ b/arch/x86/include/asm/syscalls.h @@ -21,7 +21,7 @@ asmlinkage long sys_ioperm(unsigned long, unsigned long, int); asmlinkage long sys_iopl(unsigned int); /* kernel/ldt.c */ -asmlinkage int sys_modify_ldt(int, void __user *, unsigned long); +asmlinkage long sys_modify_ldt(int, void __user *, unsigned long); /* kernel/signal.c */ asmlinkage long sys_rt_sigreturn(void); diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c index f0e64db..0402d44 100644 --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -294,8 +295,8 @@ out: return error; } -asmlinkage int sys_modify_ldt(int func, void __user *ptr, - unsigned long bytecount) +SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr , + unsigned long , bytecount) { int ret = -ENOSYS; @@ -313,5 +314,14 @@ asmlinkage int sys_modify_ldt(int func, void __user *ptr, ret = write_ldt(ptr, bytecount, 0); break; } - return ret; + /* + * The SYSCALL_DEFINE() macros give us an 'unsigned long' + * return type, but tht ABI for sys_modify_ldt() expects + * 'int'. This cast gives us an int-sized value in %rax + * for the return code. The 'unsigned' is necessary so + * the compiler does not try to sign-extend the negative + * return codes into the high half of the register when + * taking the value from int->long. + */ + return (unsigned int)ret; } diff --git a/arch/x86/um/ldt.c b/arch/x86/um/ldt.c index 836a1eb..3ee234b6 100644 --- a/arch/x86/um/ldt.c +++ b/arch/x86/um/ldt.c @@ -6,6 +6,7 @@ #include #include #include +#include #include #include #include @@ -369,7 +370,9 @@ void free_ldt(struct mm_context *mm) mm->arch.ldt.entry_count = 0; } -int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount) +SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr , + unsigned long , bytecount) { - return do_modify_ldt_skas(func, ptr, bytecount); + /* See non-um modify_ldt() for why we do this cast */ + return (unsigned int)do_modify_ldt_skas(func, ptr, bytecount); }