linux-kernel - [PATCH v2 4/5] x86/entry: Enable random_kstack

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20200324203231.64324-5-keescook@chromium.org>
Date:   Tue, 24 Mar 2020 13:32:30 -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>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jann Horn <jannh@...gle.com>,
        "Perla, Enrico" <enrico.perla@...el.com>,
        kernel-hardening@...ts.openwall.com,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 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 | 12 +++++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index beea77046f9b..b9d449581eb6 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -150,6 +150,7 @@ config X86
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64
 	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 9747876980b5..086d7af570af 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>
 
 #include <asm/desc.h>
 #include <asm/traps.h>
@@ -189,6 +190,13 @@ __visible inline 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))
@@ -283,6 +291,7 @@ __visible void do_syscall_64(unsigned long nr, struct pt_regs *regs)
 {
 	struct thread_info *ti;
 
+	add_random_kstack_offset();
 	enter_from_user_mode();
 	local_irq_enable();
 	ti = current_thread_info();
@@ -355,6 +364,7 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
 /* Handles int $0x80 */
 __visible void do_int80_syscall_32(struct pt_regs *regs)
 {
+	add_random_kstack_offset();
 	enter_from_user_mode();
 	local_irq_enable();
 	do_syscall_32_irqs_on(regs);
@@ -378,8 +388,8 @@ __visible long do_fast_syscall_32(struct pt_regs *regs)
 	 */
 	regs->ip = landing_pad;
 
+	add_random_kstack_offset();
 	enter_from_user_mode();
-
 	local_irq_enable();
 
 	/* Fetch EBP from where the vDSO stashed it. */
-- 
2.20.1