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Date: Mon, 22 Jun 2020 12:31:45 -0700
From: Kees Cook <keescook@...omium.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Kees Cook <keescook@...omium.org>,
Elena Reshetova <elena.reshetova@...el.com>,
x86@...nel.org,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Potapenko <glider@...gle.com>,
Alexander Popov <alex.popov@...ux.com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Jann Horn <jannh@...gle.com>,
kernel-hardening@...ts.openwall.com,
linux-arm-kernel@...ts.infradead.org,
linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v4 4/5] x86/entry: Enable random_kstack_offset support
Allow for a randomized stack offset on a per-syscall basis, with roughly
5 bits of entropy.
Signed-off-by: Kees Cook <keescook@...omium.org>
---
arch/x86/Kconfig | 1 +
arch/x86/entry/common.c | 11 +++++++++++
2 files changed, 12 insertions(+)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6a0cc524882d..57c2a458150e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -156,6 +156,7 @@ config X86
select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64
select HAVE_ARCH_USERFAULTFD_WP if X86_64 && USERFAULTFD
select HAVE_ARCH_VMAP_STACK if X86_64
+ select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
select HAVE_ARCH_WITHIN_STACK_FRAMES
select HAVE_ASM_MODVERSIONS
select HAVE_CMPXCHG_DOUBLE
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index bd3f14175193..681125bbf09a 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -26,6 +26,7 @@
#include <linux/livepatch.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>
+#include <linux/randomize_kstack.h>
#ifdef CONFIG_XEN_PV
#include <xen/xen-ops.h>
@@ -240,6 +241,13 @@ static void __prepare_exit_to_usermode(struct pt_regs *regs)
lockdep_assert_irqs_disabled();
lockdep_sys_exit();
+ /*
+ * x86_64 stack alignment means 3 bits are ignored, so keep
+ * the top 5 bits. x86_32 needs only 2 bits of alignment, so
+ * the top 6 bits will be used.
+ */
+ choose_random_kstack_offset(rdtsc() & 0xFF);
+
cached_flags = READ_ONCE(ti->flags);
if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
@@ -346,6 +354,7 @@ __visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
{
struct thread_info *ti;
+ add_random_kstack_offset();
enter_from_user_mode();
instrumentation_begin();
@@ -409,6 +418,7 @@ static void do_syscall_32_irqs_on(struct pt_regs *regs)
/* Handles int $0x80 */
__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
{
+ add_random_kstack_offset();
enter_from_user_mode();
instrumentation_begin();
@@ -467,6 +477,7 @@ __visible noinstr long do_fast_syscall_32(struct pt_regs *regs)
*/
regs->ip = landing_pad;
+ add_random_kstack_offset();
enter_from_user_mode();
instrumentation_begin();
--
2.25.1
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