From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753201AbdKVW2S (ORCPT ); Wed, 22 Nov 2017 17:28:18 -0500 Received: from omzsmtpe03.verizonbusiness.com ([199.249.25.208]:3676 "EHLO omzsmtpe03.verizonbusiness.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753146AbdKVW2J (ORCPT ); Wed, 22 Nov 2017 17:28:09 -0500 From: alexander.levin@verizon.com Cc: Dave Hansen , Linus Torvalds , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , alexander.levin@verizon.com X-Host: surveyor.tdc.vzwcorp.com To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" Subject: [PATCH AUTOSEL for 4.9 16/24] x86/entry: Use SYSCALL_DEFINE() macros for sys_modify_ldt() Thread-Topic: [PATCH AUTOSEL for 4.9 16/24] x86/entry: Use SYSCALL_DEFINE() macros for sys_modify_ldt() Thread-Index: AQHTY+DonNFgQx+hPkWdz7axbMotaA== Date: Wed, 22 Nov 2017 22:26:14 +0000 Message-ID: <20171122222604.20122-16-alexander.levin@verizon.com> References: <20171122222604.20122-1-alexander.levin@verizon.com> In-Reply-To: <20171122222604.20122-1-alexander.levin@verizon.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-messagesentrepresentingtype: 1 x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.144.60.250] Content-Type: text/plain; charset="iso-8859-1" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id vAMMbo1B026118 From: Dave Hansen [ Upstream commit da20ab35180780e4a6eadc804544f1fa967f3567 ] 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 Signed-off-by: Sasha Levin --- 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 91dfcafe27a6..bad25bb80679 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 6707039b9032..5f70014ca602 100644 --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -271,8 +272,8 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) 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; @@ -290,5 +291,14 @@ 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 836a1eb5df43..3ee234b6234d 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); } -- 2.11.0