Re: [PATCH v5 9/9] x86-64: Add CONFIG_UNSAFE_VSYSCALLS to feature-removal-schedule

[Ingo Molnar <mingo@elte.hu>]

* Ingo Molnar <mingo@elte.hu> wrote:

> I was unsure how big of a problem the time() slowdown was and the 
> config option was easy enough to provide. My preference would be to 
> just remove the config option and simplify the code - complexity is 
> the #1 enemy of security.

The patch below is what the config removal brings us.

Thanks,

	Ingo

--
 Documentation/feature-removal-schedule.txt |   13 -------------
 arch/x86/Kconfig                           |   23 -----------------------
 arch/x86/kernel/vsyscall_64.c              |   26 --------------------------
 arch/x86/kernel/vsyscall_emu_64.S          |    2 --
 4 files changed, 0 insertions(+), 64 deletions(-)

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 7a7446b..1a9446b 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -600,16 +600,3 @@ Why:	Superseded by the UVCIOC_CTRL_QUERY ioctl.
 Who:	Laurent Pinchart <laurent.pinchart@ideasonboard.com>
 
 ----------------------------
-
-What:	CONFIG_LEGACY_VTIME (x86_64)
-When:	When glibc 2.14 or newer is ubiquitous.  Perhaps 2013.
-Why:	Having user-executable syscall invoking code at a fixed addresses makes
-	it easier for attackers to exploit security holes.  Turning off
-	CONFIG_LEGACY_VTIME reduces the risk without breaking binary
-	compatibility but will make the time() function slightly slower on
-	glibc versions 2.13 and below.
-
-	We may flip the default setting to N before 2013.
-Who:	Andy Lutomirski <luto@mit.edu>
-
-----------------------------
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6746d35..da34972 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1646,29 +1646,6 @@ config COMPAT_VDSO
 
 	  If unsure, say Y.
 
-config LEGACY_VTIME
-	def_bool y
-	prompt "Fast legacy sys_time() vsyscall"
-	depends on X86_64
-	---help---
-	  Glibc 2.13 and older, statically linked binaries, and a few
-	  other things use a legacy ABI to implement time().
-
-	  If you say N here, the kernel will emulate that interface in
-	  order to make certain types of userspace bugs more difficult
-	  to exploit.  This will cause some legacy software to run
-	  slightly more slowly.
-
-	  If you say Y here, then the kernel will provide native code to
-	  allow legacy programs to run without any performance impact.
-	  This could make it easier to exploit certain types of
-	  userspace bugs.
-
-	  If unsure, say Y.
-
-	  NOTE: disabling this option will not break any ABI; the kernel
-	        will be fully compatible with all binaries either way.
-
 config CMDLINE_BOOL
 	bool "Built-in kernel command line"
 	---help---
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index f56644e..41f6a98 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -102,30 +102,6 @@ static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
 	       regs->ip - 2, regs->sp, regs->ax, regs->si, regs->di);
 }
 
-#ifdef CONFIG_LEGACY_VTIME
-
-/* This will break when the xtime seconds get inaccurate, but that is
- * unlikely */
-time_t __attribute__ ((unused, __section__(".vsyscall_1"))) notrace
-vtime(time_t *t)
-{
-	unsigned seq;
-	time_t result;
-
-	do {
-		seq = read_seqbegin(&VVAR(vsyscall_gtod_data).lock);
-
-		result = VVAR(vsyscall_gtod_data).wall_time_sec;
-
-	} while (read_seqretry(&VVAR(vsyscall_gtod_data).lock, seq));
-
-	if (t)
-		*t = result;
-	return result;
-}
-
-#endif /* CONFIG_LEGACY_VTIME */
-
 void dotraplinkage do_emulate_vsyscall(struct pt_regs *regs, long error_code)
 {
 	static DEFINE_RATELIMIT_STATE(rs, 3600 * HZ, 3);
@@ -169,12 +145,10 @@ void dotraplinkage do_emulate_vsyscall(struct pt_regs *regs, long error_code)
 			(struct timezone __user *)regs->si);
 		break;
 
-#ifndef CONFIG_LEGACY_VTIME
 	case 1:
 		vsyscall_name = "time";
 		ret = sys_time((time_t __user *)regs->di);
 		break;
-#endif
 
 	case 2:
 		vsyscall_name = "getcpu";
diff --git a/arch/x86/kernel/vsyscall_emu_64.S b/arch/x86/kernel/vsyscall_emu_64.S
index b192283..bc10dba 100644
--- a/arch/x86/kernel/vsyscall_emu_64.S
+++ b/arch/x86/kernel/vsyscall_emu_64.S
@@ -14,12 +14,10 @@ ENTRY(vsyscall_0)
 	int $VSYSCALL_EMU_VECTOR
 END(vsyscall_0)
 
-#ifndef CONFIG_LEGACY_VTIME
 .section .vsyscall_1, "a"
 ENTRY(vsyscall_1)
 	int $VSYSCALL_EMU_VECTOR
 END(vsyscall_1)
-#endif
 
 .section .vsyscall_2, "a"
 ENTRY(vsyscall_2)