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x86/vsyscall/64: Drop "native" vsyscalls

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Since Linux v3.2, vsyscalls have been deprecated and slow.  From v3.2
on, Linux had three vsyscall modes: "native", "emulate", and "none".

"emulate" is the default.  All known user programs work correctly in
emulate mode, but vsyscalls turn into page faults and are emulated.
This is very slow.  In "native" mode, the vsyscall page is easily
usable as an exploit gadget, but vsyscalls are a bit faster -- they
turn into normal syscalls.  (This is in contrast to vDSO functions,
which can be much faster than syscalls.)  In "none" mode, there are
no vsyscalls.

For all practical purposes, "native" was really just a chicken bit
in case something went wrong with the emulation.  It's been over six
years, and nothing has gone wrong.  Delete it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/519fee5268faea09ae550776ce969fa6e88668b0.1520449896.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski
2018-03-07 11:12:27 -08:00
committed by Ingo Molnar
parent 91c5f0de64
commit 076ca272a1
4 changed files with 10 additions and 30 deletions
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16
arch/x86/entry/vsyscall/vsyscall_64.c
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@@ -42,10 +42,8 @@
#define CREATE_TRACE_POINTS
#include "vsyscall_trace.h"
static enum { EMULATE, NATIVE, NONE } vsyscall_mode =
#if defined(CONFIG_LEGACY_VSYSCALL_NATIVE)
NATIVE;
#elif defined(CONFIG_LEGACY_VSYSCALL_NONE)
static enum { EMULATE, NONE } vsyscall_mode =
#ifdef CONFIG_LEGACY_VSYSCALL_NONE
NONE;
#else
EMULATE;
@@ -56,8 +54,6 @@ static int __init vsyscall_setup(char *str)
if (str) {
if (!strcmp("emulate", str))
vsyscall_mode = EMULATE;
else if (!strcmp("native", str))
vsyscall_mode = NATIVE;
else if (!strcmp("none", str))
vsyscall_mode = NONE;
else
@@ -139,10 +135,6 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
WARN_ON_ONCE(address != regs->ip);
/* This should be unreachable in NATIVE mode. */
if (WARN_ON(vsyscall_mode == NATIVE))
return false;
if (vsyscall_mode == NONE) {
warn_bad_vsyscall(KERN_INFO, regs,
"vsyscall attempted with vsyscall=none");
@@ -370,9 +362,7 @@ void __init map_vsyscall(void)
if (vsyscall_mode != NONE) {
__set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
vsyscall_mode == NATIVE
? PAGE_KERNEL_VSYSCALL
: PAGE_KERNEL_VVAR);
PAGE_KERNEL_VVAR);
set_vsyscall_pgtable_user_bits(swapper_pg_dir);
}