diff options
Diffstat (limited to 'debian/patches/features/x86/x86-make-x32-syscall-support-conditional.patch')
| -rw-r--r-- | debian/patches/features/x86/x86-make-x32-syscall-support-conditional.patch | 180 |
1 files changed, 180 insertions, 0 deletions
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 new file mode 100644 index 000000000..44dd25261 --- /dev/null +++ b/debian/patches/features/x86/x86-make-x32-syscall-support-conditional.patch @@ -0,0 +1,180 @@ +From: Ben Hutchings <ben@decadent.org.uk> +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: https://lore.kernel.org/lkml/1415245982.3398.53.camel@decadent.org.uk/T/#u + +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 a few instructions that mask +out the x32 flag and compare the syscall number. + +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@decadent.org.uk> +--- + .../admin-guide/kernel-parameters.txt | 4 ++ + arch/x86/Kconfig | 8 ++++ + arch/x86/entry/common.c | 3 +- + arch/x86/entry/syscall_64.c | 46 +++++++++++++++++++ + arch/x86/include/asm/elf.h | 6 ++- + arch/x86/include/asm/syscall.h | 13 ++++++ + 6 files changed, 78 insertions(+), 2 deletions(-) + +--- a/Documentation/admin-guide/kernel-parameters.txt ++++ b/Documentation/admin-guide/kernel-parameters.txt +@@ -5768,6 +5768,10 @@ + later by a loaded module cannot be set this way. + Example: sysctl.vm.swappiness=40 + ++ 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 +--- a/arch/x86/Kconfig ++++ b/arch/x86/Kconfig +@@ -2865,6 +2865,14 @@ config COMPAT_32 + select HAVE_UID16 + select OLD_SIGSUSPEND3 + ++config X86_X32_DISABLED ++ bool "x32 ABI disabled by default" ++ depends on X86_X32_ABI ++ 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_ABI +--- a/arch/x86/entry/common.c ++++ b/arch/x86/entry/common.c +@@ -62,7 +62,7 @@ static __always_inline bool do_syscall_x + */ + unsigned int xnr = nr - __X32_SYSCALL_BIT; + +- if (IS_ENABLED(CONFIG_X86_X32_ABI) && likely(xnr < X32_NR_syscalls)) { ++ if (IS_ENABLED(CONFIG_X86_X32_ABI) && unlikely(x32_enabled) && likely(xnr < X32_NR_syscalls)) { + xnr = array_index_nospec(xnr, X32_NR_syscalls); + regs->ax = x32_sys_call_table[xnr](regs); + return true; +--- a/arch/x86/entry/syscall_x32.c ++++ b/arch/x86/entry/syscall_x32.c +@@ -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/syscalls.h> + #include <asm/syscall.h> + +@@ -16,3 +19,46 @@ + asmlinkage const sys_call_ptr_t x32_sys_call_table[] = { + #include <asm/syscalls_x32.h> + }; ++ ++/* Maybe enable x32 syscalls */ ++ ++#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_param_set(const char *val, const struct kernel_param *p) ++{ ++ 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; ++} ++ ++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); +--- a/arch/x86/include/asm/elf.h ++++ b/arch/x86/include/asm/elf.h +@@ -11,6 +11,9 @@ + #include <asm/user.h> + #include <asm/auxvec.h> + #include <asm/fsgsbase.h> ++#ifndef COMPILE_OFFSETS /* avoid a circular dependency on asm-offsets.h */ ++#include <asm/syscall.h> ++#endif + + typedef unsigned long elf_greg_t; + +@@ -161,7 +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)) ++ (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" +--- a/arch/x86/include/asm/syscall.h ++++ b/arch/x86/include/asm/syscall.h +@@ -13,6 +13,7 @@ + #include <uapi/linux/audit.h> + #include <linux/sched.h> + #include <linux/err.h> ++#include <linux/jump_label.h> + #include <asm/thread_info.h> /* for TS_COMPAT */ + #include <asm/unistd.h> + +@@ -30,6 +31,18 @@ extern const sys_call_ptr_t ia32_sys_cal + extern const sys_call_ptr_t x32_sys_call_table[]; + #endif + ++#if defined(CONFIG_X86_X32_ABI) ++#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 ++ + /* + * 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 |