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Message-Id: <617e07c1fcf585f78a2567b6bbc2b94ca90148bb.1402971639.git.luto@amacapital.net> Date: Mon, 16 Jun 2014 19:23:14 -0700 From: Andy Lutomirski <luto@...capital.net> To: x86@...nel.org, linux-kernel@...r.kernel.org Cc: Andy Lutomirski <luto@...capital.net> Subject: [PATCH 7/8] x86_64,vsyscall: Rewrite comment and clean up headers in vsyscall code vsyscall_64.c is just vsyscall emulation. Tidy it up accordingly. If my comment editing offends anyone, let me know and I can fix it. Signed-off-by: Andy Lutomirski <luto@...capital.net> --- arch/x86/kernel/vsyscall_64.c | 51 +++++++++++++++---------------------------- 1 file changed, 18 insertions(+), 33 deletions(-) diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c index 5029be3..1ea34e7 100644 --- a/arch/x86/kernel/vsyscall_64.c +++ b/arch/x86/kernel/vsyscall_64.c @@ -1,52 +1,37 @@ /* - * Copyright (C) 2001 Andrea Arcangeli <andrea@...e.de> SuSE - * Copyright 2003 Andi Kleen, SuSE Labs. + * Mostly copyright (c) 2012-2014 Andy Lutomirski <luto@...capital.net> * - * [ NOTE: this mechanism is now deprecated in favor of the vDSO. ] + * This file implements vsyscall emulation. vsyscalls are a legacy ABI: + * userspace can request certain kernel services by calling fixed + * addresses. This concept is problematic: * - * Thanks to hpa@...nsmeta.com for some useful hint. - * Special thanks to Ingo Molnar for his early experience with - * a different vsyscall implementation for Linux/IA32 and for the name. + * - It interferes with ASLR. + * - It's awkward to write code that lives in kernel addresses but is + * callable by userspace at fixed addresses. + * - The whole concept is impossible for 32-bit compat userspace. + * - UML cannot easily virtualize a vsyscall. * - * vsyscall 1 is located at -10Mbyte, vsyscall 2 is located - * at virtual address -10Mbyte+1024bytes etc... There are at max 4 - * vsyscalls. One vsyscall can reserve more than 1 slot to avoid - * jumping out of line if necessary. We cannot add more with this - * mechanism because older kernels won't return -ENOSYS. + * As of mid-2014, I believe that there is no new userspace code that + * will use a vsyscall if the vDSO is present. I hope that there will + * soon be no new userspace code that will ever use a vsyscall. * - * Note: the concept clashes with user mode linux. UML users should - * use the vDSO. + * The code in this file emulates vsyscalls when notified of a page + * fault to a vsyscall address. + * + * The original version of this code is: + * Copyright (C) 2001 Andrea Arcangeli <andrea@...e.de> SuSE + * Copyright 2003 Andi Kleen, SuSE Labs. */ -#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt -#include <linux/time.h> -#include <linux/init.h> #include <linux/kernel.h> #include <linux/timer.h> -#include <linux/seqlock.h> -#include <linux/jiffies.h> -#include <linux/sysctl.h> -#include <linux/topology.h> -#include <linux/timekeeper_internal.h> -#include <linux/getcpu.h> -#include <linux/cpu.h> -#include <linux/smp.h> -#include <linux/notifier.h> #include <linux/syscalls.h> #include <linux/ratelimit.h> #include <asm/vsyscall.h> -#include <asm/pgtable.h> -#include <asm/compat.h> -#include <asm/page.h> #include <asm/unistd.h> #include <asm/fixmap.h> -#include <asm/errno.h> -#include <asm/io.h> -#include <asm/segment.h> -#include <asm/desc.h> -#include <asm/topology.h> #include <asm/traps.h> #define CREATE_TRACE_POINTS -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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