[linux] 01/01: [x86] Rewrite "Make x32 syscall support conditional ..." to use a static key
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commit 7708ade8437d4c76a1b31bc16bdf19b4eb600c2d
Author: Ben Hutchings <ben at decadent.org.uk>
Date: Tue Feb 13 00:04:16 2018 +0000
[x86] Rewrite "Make x32 syscall support conditional ..." to use a static key
Now that the old slow path is always used, this is an important
optimisation.
---
debian/changelog | 2 +
.../x86-make-x32-syscall-support-conditional.patch | 169 ++++++++++++---------
2 files changed, 96 insertions(+), 75 deletions(-)
diff --git a/debian/changelog b/debian/changelog
index 69138be..cbd079d 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -145,6 +145,8 @@ linux (4.15.2-1~exp1) UNRELEASED; urgency=medium
* Enable CGROUP_BPF (except for armel) (Closes: #872560)
* usb: Enable USBIP_CORE, USBIP_VHCI_HCD, USBIP_HOST, USBIP_VUDC as
modules on all architectures (Closes: #888042)
+ * [x86] Rewrite "Make x32 syscall support conditional on a kernel parameter"
+ to use a static key
-- Bastian Blank <waldi at debian.org> Thu, 18 Jan 2018 09:14:57 +0100
diff --git a/debian/patches/features/x86/x86-make-x32-syscall-support-conditional.patch b/debian/patches/features/x86/x86-make-x32-syscall-support-conditional.patch
index b97167b..71c5691 100644
--- a/debian/patches/features/x86/x86-make-x32-syscall-support-conditional.patch
+++ b/debian/patches/features/x86/x86-make-x32-syscall-support-conditional.patch
@@ -1,8 +1,7 @@
From: Ben Hutchings <ben at decadent.org.uk>
-Date: Fri, 25 Jul 2014 01:16:15 +0100
+Date: Mon, 12 Feb 2018 23:59:26 +0000
Subject: x86: Make x32 syscall support conditional on a kernel parameter
Bug-Debian: https://bugs.debian.org/708070
-Forwarded: http://mid.gmane.org/1415245982.3398.53.camel@decadent.org.uk
Enabling x32 in the standard amd64 kernel would increase its attack
surface while provide no benefit to the vast majority of its users.
@@ -10,25 +9,24 @@ No-one seems interested in regularly checking for vulnerabilities
specific to x32 (at least no-one with a white hat).
Still, adding another flavour just to turn on x32 seems wasteful. And
-the only differences on syscall entry are two instructions (mask out
-the x32 flag and compare the syscall number).
+the only differences on syscall entry are a few instructions that mask
+out the x32 flag and compare the syscall number.
-So pad the standard comparison with a nop and add a kernel parameter
-"syscall.x32" which controls whether this is replaced with the x32
-version at boot time. Add a Kconfig parameter to set the default.
+Use a static key to control whether x32 syscalls are really enabled, a
+Kconfig parameter to set its default value and a kernel parameter
+"syscall.x32" to change it at boot time.
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>
---
- Documentation/admin-guide/kernel-parameters.txt | 4 ++++
- arch/x86/Kconfig | 8 +++++++
- arch/x86/entry/common.c | 16 +++++++++++--
- arch/x86/entry/syscall_64.c | 31 +++++++++++++++++++++++++
- arch/x86/include/asm/elf.h | 3 ++-
- arch/x86/include/asm/syscall.h | 6 +++++
- 6 files changed, 65 insertions(+), 3 deletions(-)
+ Documentation/admin-guide/kernel-parameters.txt | 4 ++
+ arch/x86/Kconfig | 8 ++++
+ arch/x86/entry/common.c | 11 +++++-
+ arch/x86/entry/syscall_64.c | 41 ++++++++++++++++++++++++
+ arch/x86/include/asm/elf.h | 4 +-
+ arch/x86/include/asm/syscall.h | 13 +++++++
+ arch/x86/include/asm/unistd.h | 4 +-
+ 7 files changed, 80 insertions(+), 5 deletions(-)
-diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
-index 1e762c210f1b..9fd9eb61606d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4096,6 +4096,10 @@
@@ -42,8 +40,6 @@ index 1e762c210f1b..9fd9eb61606d 100644
sysfs.deprecated=0|1 [KNL]
Enable/disable old style sysfs layout for old udev
on older distributions. When this option is enabled
-diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
-index 20da391b5f32..16f0c88fcc3d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2863,6 +2863,14 @@ config COMPAT_32
@@ -61,60 +57,39 @@ index 20da391b5f32..16f0c88fcc3d 100644
config COMPAT
def_bool y
depends on IA32_EMULATION || X86_X32
-diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
-index 21dbdf0e476b..a26c084ecca5 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
-@@ -270,6 +270,7 @@ __visible void do_syscall_64(struct pt_regs *regs)
- {
- struct thread_info *ti = current_thread_info();
- unsigned long nr = regs->orig_ax;
-+ unsigned int syscall_mask, nr_syscalls_enabled;
-
- enter_from_user_mode();
- local_irq_enable();
-@@ -282,8 +283,19 @@ __visible void do_syscall_64(struct pt_regs *regs)
+@@ -282,8 +282,15 @@ __visible void do_syscall_64(struct pt_r
* table. The only functional difference is the x32 bit in
* regs->orig_ax, which changes the behavior of some syscalls.
*/
- if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
- nr = array_index_nospec(nr & __SYSCALL_MASK, NR_syscalls);
-+ if (__SYSCALL_MASK == ~0U || x32_enabled) {
-+ syscall_mask = __SYSCALL_MASK;
-+ nr_syscalls_enabled = NR_syscalls;
-+ } else {
-+ /*
-+ * x32 syscalls present but not enabled. Don't mask out
-+ * the x32 flag and don't enable any x32-specific calls.
-+ */
-+ syscall_mask = ~0U;
-+ nr_syscalls_enabled = 512;
-+ }
-+ if (likely((nr & syscall_mask) < nr_syscalls_enabled)) {
-+ nr = array_index_nospec(nr & syscall_mask, nr_syscalls_enabled);
++ if (x32_enabled) {
++ if (likely((nr & ~__X32_SYSCALL_BIT) < NR_syscalls)) {
++ nr = array_index_nospec(nr & ~__X32_SYSCALL_BIT,
++ NR_syscalls);
++ goto good;
++ }
++ } else if (likely((nr & ~0U) < NR_non_x32_syscalls)) {
++ nr = array_index_nospec(nr & ~0U, NR_non_x32_syscalls);
++ good:
regs->ax = sys_call_table[nr](
regs->di, regs->si, regs->dx,
regs->r10, regs->r8, regs->r9);
-diff --git a/arch/x86/entry/syscall_64.c b/arch/x86/entry/syscall_64.c
-index c176d2fab1da..0f15e2686d09 100644
--- a/arch/x86/entry/syscall_64.c
+++ b/arch/x86/entry/syscall_64.c
-@@ -4,8 +4,14 @@
+@@ -4,6 +4,9 @@
#include <linux/linkage.h>
#include <linux/sys.h>
#include <linux/cache.h>
+#include <linux/moduleparam.h>
+#undef MODULE_PARAM_PREFIX
+#define MODULE_PARAM_PREFIX "syscall."
-+#include <linux/bug.h>
-+#include <linux/init.h>
#include <asm/asm-offsets.h>
#include <asm/syscall.h>
-+#include <asm/text-patching.h>
- #define __SYSCALL_64(nr, sym, qual) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
- #include <asm/syscalls_64.h>
-@@ -23,3 +29,28 @@ asmlinkage const sys_call_ptr_t sys_call_table[__NR_syscall_max+1] = {
+@@ -23,3 +26,50 @@ asmlinkage const sys_call_ptr_t sys_call
[0 ... __NR_syscall_max] = &sys_ni_syscall,
#include <asm/syscalls_64.h>
};
@@ -123,28 +98,48 @@ index c176d2fab1da..0f15e2686d09 100644
+
+/* Maybe enable x32 syscalls */
+
-+bool x32_enabled = !IS_ENABLED(CONFIG_X86_X32_DISABLED);
-+module_param_named(x32, x32_enabled, bool, 0444);
++#if defined(CONFIG_X86_X32_DISABLED)
++DEFINE_STATIC_KEY_FALSE(x32_enabled_skey);
++#else
++DEFINE_STATIC_KEY_TRUE(x32_enabled_skey);
++#endif
+
-+static int __init x32_enable(void)
++static int __init x32_param_set(const char *val, const struct kernel_param *p)
+{
-+ if (x32_enabled) {
-+#ifdef CONFIG_X86_X32_DISABLED
-+ pr_info("Enabled x32 syscalls\n");
-+#endif
-+ }
-+#ifndef CONFIG_X86_X32_DISABLED
-+ else
-+ pr_info("Disabled x32 syscalls\n");
-+#endif
++ bool enabled;
++ int ret;
+
++ ret = kstrtobool(val, &enabled);
++ if (ret)
++ return ret;
++ if (IS_ENABLED(CONFIG_X86_X32_DISABLED)) {
++ if (enabled) {
++ static_key_enable(&x32_enabled_skey.key);
++ pr_info("Enabled x32 syscalls\n");
++ }
++ } else {
++ if (!enabled) {
++ static_key_disable(&x32_enabled_skey.key);
++ pr_info("Disabled x32 syscalls\n");
++ }
++ }
+ return 0;
+}
-+late_initcall(x32_enable);
++
++static int x32_param_get(char *buffer, const struct kernel_param *p)
++{
++ return sprintf(buffer, "%c\n",
++ static_key_enabled(&x32_enabled_skey) ? 'Y' : 'N');
++}
++
++static const struct kernel_param_ops x32_param_ops = {
++ .set = x32_param_set,
++ .get = x32_param_get,
++};
++
++arch_param_cb(x32, &x32_param_ops, NULL, 0444);
+
+#endif
-diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
-index 0d157d2a1e2a..17e23826a802 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -10,6 +10,7 @@
@@ -155,25 +150,38 @@ index 0d157d2a1e2a..17e23826a802 100644
typedef unsigned long elf_greg_t;
-@@ -163,7 +164,7 @@ do { \
+@@ -163,7 +164,8 @@ do { \
#define compat_elf_check_arch(x) \
(elf_check_arch_ia32(x) || \
- (IS_ENABLED(CONFIG_X86_X32_ABI) && (x)->e_machine == EM_X86_64))
-+ (x32_enabled && (x)->e_machine == EM_X86_64))
++ (IS_ENABLED(CONFIG_X86_X32_ABI) && x32_enabled && \
++ (x)->e_machine == EM_X86_64))
#if __USER32_DS != __USER_DS
# error "The following code assumes __USER32_DS == __USER_DS"
-diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
-index 03eedc21246d..c5bce400ebb4 100644
--- a/arch/x86/include/asm/syscall.h
+++ b/arch/x86/include/asm/syscall.h
-@@ -35,6 +35,12 @@ extern const sys_call_ptr_t sys_call_table[];
+@@ -16,6 +16,7 @@
+ #include <uapi/linux/audit.h>
+ #include <linux/sched.h>
+ #include <linux/err.h>
++#include <linux/jump_label.h>
+ #include <asm/asm-offsets.h> /* For NR_syscalls */
+ #include <asm/thread_info.h> /* for TS_COMPAT */
+ #include <asm/unistd.h>
+@@ -35,6 +36,18 @@ extern const sys_call_ptr_t sys_call_tab
extern const sys_call_ptr_t ia32_sys_call_table[];
#endif
+#if defined(CONFIG_X86_X32_ABI)
-+extern bool x32_enabled;
++#if defined(CONFIG_X86_X32_DISABLED)
++DECLARE_STATIC_KEY_FALSE(x32_enabled_skey);
++#define x32_enabled static_branch_unlikely(&x32_enabled_skey)
++#else
++DECLARE_STATIC_KEY_TRUE(x32_enabled_skey);
++#define x32_enabled static_branch_likely(&x32_enabled_skey)
++#endif
+#else
+#define x32_enabled 0
+#endif
@@ -181,6 +189,17 @@ index 03eedc21246d..c5bce400ebb4 100644
/*
* Only the low 32 bits of orig_ax are meaningful, so we return int.
* This importantly ignores the high bits on 64-bit, so comparisons
---
-2.16.1
-
+--- a/arch/x86/include/asm/unistd.h
++++ b/arch/x86/include/asm/unistd.h
+@@ -6,9 +6,9 @@
+
+
+ # ifdef CONFIG_X86_X32_ABI
+-# define __SYSCALL_MASK (~(__X32_SYSCALL_BIT))
++# define NR_non_x32_syscalls 512
+ # else
+-# define __SYSCALL_MASK (~0)
++# define NR_non_x32_syscalls NR_syscalls
+ # endif
+
+ # ifdef CONFIG_X86_32
--
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