debian-packaging
/
linux
8
0
Fork 0
Code Releases Activity
linux/debian/patches/features/x86/x86-make-x32-syscall-suppor...

187 lines
6.2 KiB
Diff
Raw Blame History

From: Ben Hutchings <ben@decadent.org.uk>
Date: Fri, 25 Jul 2014 01:16:15 +0100
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.
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).
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.
Signed-off-by: Ben Hutchings <ben@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(-)
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 @@
switches= [HW,M68k]
+ syscall.x32= [KNL,x86_64] Enable/disable use of x32 syscalls on
+ an x86_64 kernel where CONFIG_X86_X32 is enabled.
+ Default depends on CONFIG_X86_X32_DISABLED.
+
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
select HAVE_UID16
select OLD_SIGSUSPEND3
+config X86_X32_DISABLED
+ bool "x32 ABI disabled by default"
+ depends on X86_X32
+ default n
+ help
+ Disable the x32 ABI unless explicitly enabled using the
+ kernel paramter "syscall.x32=y".
+
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)
* 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);
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 @@
#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] = {
[0 ... __NR_syscall_max] = &sys_ni_syscall,
#include <asm/syscalls_64.h>
};
+
+#ifdef CONFIG_X86_X32_ABI
+
+/* Maybe enable x32 syscalls */
+
+bool x32_enabled = !IS_ENABLED(CONFIG_X86_X32_DISABLED);
+module_param_named(x32, x32_enabled, bool, 0444);
+
+static int __init x32_enable(void)
+{
+ 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
+
+ return 0;
+}
+late_initcall(x32_enable);
+
+#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 @@
#include <asm/ptrace.h>
#include <asm/user.h>
#include <asm/auxvec.h>
+#include <asm/syscall.h>
typedef unsigned long elf_greg_t;
@@ -163,7 +164,7 @@ 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))
#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[];
extern const sys_call_ptr_t ia32_sys_call_table[];
#endif
+#if defined(CONFIG_X86_X32_ABI)
+extern bool x32_enabled;
+#else
+#define x32_enabled 0
+#endif
+
/*
* 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
View Git Blame Copy Permalink