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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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
arch/x86/Kconfig
View File

@ -2266,7 +2266,7 @@ choice
it can be used to assist security vulnerability exploitation.
This setting can be changed at boot time via the kernel command
line parameter vsyscall=[native|emulate|none].
line parameter vsyscall=[emulate|none].
On a system with recent enough glibc (2.14 or newer) and no
static binaries, you can say None without a performance penalty
@ -2274,15 +2274,6 @@ choice
If unsure, select "Emulate".
config LEGACY_VSYSCALL_NATIVE
bool "Native"
help
Actual executable code is located in the fixed vsyscall
address mapping, implementing time() efficiently. Since
this makes the mapping executable, it can be used during
security vulnerability exploitation (traditionally as
ROP gadgets). This configuration is not recommended.
config LEGACY_VSYSCALL_EMULATE
bool "Emulate"
help

16
arch/x86/entry/vsyscall/vsyscall_64.c
View File

@ -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);
}

2
arch/x86/include/asm/pgtable_types.h
View File

@ -174,7 +174,6 @@ enum page_cache_mode {
#define __PAGE_KERNEL_RO (__PAGE_KERNEL & ~_PAGE_RW)
#define __PAGE_KERNEL_RX (__PAGE_KERNEL_EXEC & ~_PAGE_RW)
#define __PAGE_KERNEL_NOCACHE (__PAGE_KERNEL | _PAGE_NOCACHE)
#define __PAGE_KERNEL_VSYSCALL (__PAGE_KERNEL_RX | _PAGE_USER)
#define __PAGE_KERNEL_VVAR (__PAGE_KERNEL_RO | _PAGE_USER)
#define __PAGE_KERNEL_LARGE (__PAGE_KERNEL | _PAGE_PSE)
#define __PAGE_KERNEL_LARGE_EXEC (__PAGE_KERNEL_EXEC | _PAGE_PSE)
@ -206,7 +205,6 @@ enum page_cache_mode {
#define PAGE_KERNEL_NOCACHE __pgprot(__PAGE_KERNEL_NOCACHE | _PAGE_ENC)
#define PAGE_KERNEL_LARGE __pgprot(__PAGE_KERNEL_LARGE | _PAGE_ENC)
#define PAGE_KERNEL_LARGE_EXEC __pgprot(__PAGE_KERNEL_LARGE_EXEC | _PAGE_ENC)
#define PAGE_KERNEL_VSYSCALL __pgprot(__PAGE_KERNEL_VSYSCALL | _PAGE_ENC)
#define PAGE_KERNEL_VVAR __pgprot(__PAGE_KERNEL_VVAR | _PAGE_ENC)
#define PAGE_KERNEL_IO __pgprot(__PAGE_KERNEL_IO)

11
tools/testing/selftests/x86/test_vsyscall.c
View File

@ -450,7 +450,7 @@ static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
num_vsyscall_traps++;
}
static int test_native_vsyscall(void)
static int test_emulation(void)
{
time_t tmp;
bool is_native;
@ -458,7 +458,7 @@ static int test_native_vsyscall(void)
if (!vtime)
return 0;
printf("[RUN]\tchecking for native vsyscall\n");
printf("[RUN]\tchecking that vsyscalls are emulated\n");
sethandler(SIGTRAP, sigtrap, 0);
set_eflags(get_eflags() | X86_EFLAGS_TF);
vtime(&tmp);
@ -474,11 +474,12 @@ static int test_native_vsyscall(void)
*/
is_native = (num_vsyscall_traps > 1);
printf("\tvsyscalls are %s (%d instructions in vsyscall page)\n",
printf("[%s]\tvsyscalls are %s (%d instructions in vsyscall page)\n",
(is_native ? "FAIL" : "OK"),
(is_native ? "native" : "emulated"),
(int)num_vsyscall_traps);
return 0;
return is_native;
}
#endif
@ -498,7 +499,7 @@ int main(int argc, char **argv)
nerrs += test_vsys_r();
#ifdef __x86_64__
nerrs += test_native_vsyscall();
nerrs += test_emulation();
#endif
return nerrs ? 1 : 0;