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From: Kees Cook <keescook@chromium.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Kees Cook <keescook@chromium.org>,
	Elena Reshetova <elena.reshetova@intel.com>,
	x86@kernel.org, Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Potapenko <glider@google.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Jann Horn <jannh@google.com>,
	"Perla, Enrico" <enrico.perla@intel.com>,
	kernel-hardening@lists.openwall.com,
	linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2 4/5] x86/entry: Enable random_kstack_offset support
Date: Tue, 24 Mar 2020 13:32:30 -0700
Message-ID: <20200324203231.64324-5-keescook@chromium.org> (raw)
In-Reply-To: <20200324203231.64324-1-keescook@chromium.org>

Allow for a randomized stack offset on a per-syscall basis, with roughly
5 bits of entropy.

Signed-off-by: Kees Cook <keescook@chromium.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


  parent reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-24 20:32 [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall Kees Cook
2020-03-24 20:32 ` [PATCH v2 1/5] jump_label: Provide CONFIG-driven build state defaults Kees Cook
2020-03-24 22:06   ` Peter Zijlstra
2020-03-24 20:32 ` [PATCH v2 2/5] init_on_alloc: Unpessimize default-on builds Kees Cook
2020-03-26 15:48   ` Alexander Potapenko
2020-03-24 20:32 ` [PATCH v2 3/5] stack: Optionally randomize kernel stack offset each syscall Kees Cook
2020-03-30 11:25   ` Mark Rutland
2020-03-30 18:18     ` Kees Cook
2020-03-30 18:27     ` Kees Cook
2020-03-24 20:32 ` Kees Cook [this message]
2020-03-28 22:26   ` [PATCH v2 4/5] x86/entry: Enable random_kstack_offset support Kees Cook
2020-03-24 20:32 ` [PATCH v2 5/5] arm64: entry: " Kees Cook
2020-03-25 13:21   ` Mark Rutland
2020-03-25 20:22     ` Kees Cook
2020-03-26 11:15       ` Mark Rutland
2020-03-26 16:31         ` Kees Cook
2020-03-30 11:26           ` Mark Rutland
2020-04-20 20:54   ` Will Deacon
2020-04-20 22:34     ` Kees Cook
2020-04-21  7:02       ` Will Deacon
2020-03-24 21:28 ` [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall Jann Horn
2020-03-24 23:07   ` Kees Cook
2020-03-25 12:15     ` Reshetova, Elena
2020-03-25 20:27       ` Kees Cook
2020-03-25 23:20         ` Jann Horn
2020-03-26 17:18           ` Kees Cook

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