initial commit
imported from https://salsa.debian.org/kernel-team/linux.git commit 9d5cc9d9d6501d7f1dd7e194d4b245bd0b6c6a22 version 6.11.4-1
This commit is contained in:
180
debian/patches/features/x86/x86-make-x32-syscall-support-conditional.patch
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180
debian/patches/features/x86/x86-make-x32-syscall-support-conditional.patch
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@@ -0,0 +1,180 @@
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From: Ben Hutchings <ben@decadent.org.uk>
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Date: Mon, 12 Feb 2018 23:59:26 +0000
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Subject: x86: Make x32 syscall support conditional on a kernel parameter
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Bug-Debian: https://bugs.debian.org/708070
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Forwarded: https://lore.kernel.org/lkml/1415245982.3398.53.camel@decadent.org.uk/T/#u
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Enabling x32 in the standard amd64 kernel would increase its attack
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surface while provide no benefit to the vast majority of its users.
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No-one seems interested in regularly checking for vulnerabilities
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specific to x32 (at least no-one with a white hat).
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Still, adding another flavour just to turn on x32 seems wasteful. And
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the only differences on syscall entry are a few instructions that mask
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out the x32 flag and compare the syscall number.
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Use a static key to control whether x32 syscalls are really enabled, a
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Kconfig parameter to set its default value and a kernel parameter
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"syscall.x32" to change it at boot time.
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Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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---
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.../admin-guide/kernel-parameters.txt | 4 ++
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arch/x86/Kconfig | 8 ++++
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arch/x86/entry/common.c | 3 +-
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arch/x86/entry/syscall_64.c | 46 +++++++++++++++++++
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arch/x86/include/asm/elf.h | 6 ++-
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arch/x86/include/asm/syscall.h | 13 ++++++
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6 files changed, 78 insertions(+), 2 deletions(-)
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--- a/Documentation/admin-guide/kernel-parameters.txt
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+++ b/Documentation/admin-guide/kernel-parameters.txt
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@@ -6498,6 +6498,10 @@
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later by a loaded module cannot be set this way.
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Example: sysctl.vm.swappiness=40
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+ syscall.x32= [KNL,x86_64] Enable/disable use of x32 syscalls on
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+ an x86_64 kernel where CONFIG_X86_X32 is enabled.
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+ Default depends on CONFIG_X86_X32_DISABLED.
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+
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sysrq_always_enabled
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[KNL]
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Ignore sysrq setting - this boot parameter will
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--- a/arch/x86/Kconfig
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+++ b/arch/x86/Kconfig
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@@ -3058,6 +3058,14 @@ config COMPAT_32
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select HAVE_UID16
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select OLD_SIGSUSPEND3
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+config X86_X32_DISABLED
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+ bool "x32 ABI disabled by default"
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+ depends on X86_X32_ABI
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+ default n
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+ help
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+ Disable the x32 ABI unless explicitly enabled using the
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+ kernel paramter "syscall.x32=y".
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+
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config COMPAT
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def_bool y
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depends on IA32_EMULATION || X86_X32_ABI
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--- a/arch/x86/entry/common.c
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+++ b/arch/x86/entry/common.c
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@@ -64,7 +64,7 @@ static __always_inline bool do_syscall_x
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*/
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unsigned int xnr = nr - __X32_SYSCALL_BIT;
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- if (IS_ENABLED(CONFIG_X86_X32_ABI) && likely(xnr < X32_NR_syscalls)) {
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+ if (IS_ENABLED(CONFIG_X86_X32_ABI) && unlikely(x32_enabled) && likely(xnr < X32_NR_syscalls)) {
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xnr = array_index_nospec(xnr, X32_NR_syscalls);
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regs->ax = x32_sys_call(regs, xnr);
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return true;
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--- a/arch/x86/entry/syscall_x32.c
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+++ b/arch/x86/entry/syscall_x32.c
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@@ -4,6 +4,9 @@
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#include <linux/linkage.h>
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#include <linux/sys.h>
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#include <linux/cache.h>
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+#include <linux/moduleparam.h>
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+#undef MODULE_PARAM_PREFIX
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+#define MODULE_PARAM_PREFIX "syscall."
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#include <linux/syscalls.h>
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#include <asm/syscall.h>
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@@ -20,3 +23,46 @@
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default: return __x64_sys_ni_syscall(regs);
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}
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};
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+
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+/* Maybe enable x32 syscalls */
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+
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+#if defined(CONFIG_X86_X32_DISABLED)
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+DEFINE_STATIC_KEY_FALSE(x32_enabled_skey);
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+#else
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+DEFINE_STATIC_KEY_TRUE(x32_enabled_skey);
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+#endif
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+
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+static int __init x32_param_set(const char *val, const struct kernel_param *p)
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+{
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+ bool enabled;
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+ int ret;
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+
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+ ret = kstrtobool(val, &enabled);
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+ if (ret)
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+ return ret;
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+ if (IS_ENABLED(CONFIG_X86_X32_DISABLED)) {
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+ if (enabled) {
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+ static_key_enable(&x32_enabled_skey.key);
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+ pr_info("Enabled x32 syscalls\n");
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+ }
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+ } else {
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+ if (!enabled) {
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+ static_key_disable(&x32_enabled_skey.key);
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+ pr_info("Disabled x32 syscalls\n");
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+ }
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+ }
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+ return 0;
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+}
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+
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+static int x32_param_get(char *buffer, const struct kernel_param *p)
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+{
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+ return sprintf(buffer, "%c\n",
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+ static_key_enabled(&x32_enabled_skey) ? 'Y' : 'N');
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+}
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+
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+static const struct kernel_param_ops x32_param_ops = {
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+ .set = x32_param_set,
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+ .get = x32_param_get,
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+};
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+
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+arch_param_cb(x32, &x32_param_ops, NULL, 0444);
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--- a/arch/x86/include/asm/elf.h
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+++ b/arch/x86/include/asm/elf.h
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@@ -12,6 +12,9 @@
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#include <asm/user.h>
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#include <asm/auxvec.h>
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#include <asm/fsgsbase.h>
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+#ifndef COMPILE_OFFSETS /* avoid a circular dependency on asm-offsets.h */
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+#include <asm/syscall.h>
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+#endif
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typedef unsigned long elf_greg_t;
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@@ -151,7 +154,8 @@ do { \
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#define compat_elf_check_arch(x) \
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((elf_check_arch_ia32(x) && ia32_enabled_verbose()) || \
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- (IS_ENABLED(CONFIG_X86_X32_ABI) && (x)->e_machine == EM_X86_64))
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+ (IS_ENABLED(CONFIG_X86_X32_ABI) && x32_enabled && \
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+ (x)->e_machine == EM_X86_64))
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static inline void elf_common_init(struct thread_struct *t,
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struct pt_regs *regs, const u16 ds)
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--- a/arch/x86/include/asm/syscall.h
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+++ b/arch/x86/include/asm/syscall.h
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@@ -13,6 +13,7 @@
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#include <uapi/linux/audit.h>
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#include <linux/sched.h>
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#include <linux/err.h>
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+#include <linux/jump_label.h>
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#include <asm/thread_info.h> /* for TS_COMPAT */
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#include <asm/unistd.h>
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@@ -28,6 +29,18 @@ extern const sys_call_ptr_t ia32_sys_cal
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extern long x32_sys_call(const struct pt_regs *, unsigned int nr);
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extern long x64_sys_call(const struct pt_regs *, unsigned int nr);
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+#if defined(CONFIG_X86_X32_ABI)
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+#if defined(CONFIG_X86_X32_DISABLED)
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+DECLARE_STATIC_KEY_FALSE(x32_enabled_skey);
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+#define x32_enabled static_branch_unlikely(&x32_enabled_skey)
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+#else
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+DECLARE_STATIC_KEY_TRUE(x32_enabled_skey);
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+#define x32_enabled static_branch_likely(&x32_enabled_skey)
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+#endif
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+#else
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+#define x32_enabled 0
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+#endif
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+
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/*
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* Only the low 32 bits of orig_ax are meaningful, so we return int.
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* This importantly ignores the high bits on 64-bit, so comparisons
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