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>
Replace a couple of magically connected buffer length literal constants with
a common definition that makes their relationship obvious. Also document
why our sscanf() usage is safe.
No intended functional changes.
Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Andrew Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kselftest@vger.kernel.org
Cc: shuah@kernel.org
Link: http://lkml.kernel.org/r/20180211205924.GA23210@light.dominikbrodowski.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This tests that the vsyscall entries do what they're expected to do.
It also confirms that attempts to read the vsyscall page behave as
expected.
If changes are made to the vsyscall code or its memory map handling,
running this test in all three of vsyscall=none, vsyscall=emulate,
and vsyscall=native are helpful.
(Because it's easy, this also compares the vsyscall results to their
vDSO equivalents.)
Note to KAISER backporters: please test this under all three
vsyscall modes. Also, in the emulate and native modes, make sure
that test_vsyscall_64 agrees with the command line or config
option as to which mode you're in. It's quite easy to mess up
the kernel such that native mode accidentally emulates
or vice versa.
Greg, etc: please backport this to all your Meltdown-patched
kernels. It'll help make sure the patches didn't regress
vsyscalls.
CSigned-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/2b9c5a174c1d60fd7774461d518aa75598b1d8fd.1515719552.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
