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Date: Fri, 6 Apr 2018 17:22:22 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: kernel-hardening@...ts.openwall.com,
Kees Cook <keescook@...omium.org>,
PaX Team <pageexec@...email.hu>,
Brad Spengler <spender@...ecurity.net>,
Ingo Molnar <mingo@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
Tycho Andersen <tycho@...ho.ws>,
Laura Abbott <labbott@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Borislav Petkov <bp@...en8.de>,
Richard Sandiford <richard.sandiford@....com>,
Thomas Gleixner <tglx@...utronix.de>,
"H . Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
"Dmitry V . Levin" <ldv@...linux.org>,
Emese Revfy <re.emese@...il.com>,
Jonathan Corbet <corbet@....net>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Thomas Garnier <thgarnie@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexei Starovoitov <ast@...nel.org>,
Josef Bacik <jbacik@...com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Nicholas Piggin <npiggin@...il.com>,
Al Viro <viro@...iv.linux.org.uk>,
"David S . Miller" <davem@...emloft.net>,
Ding Tianhong <dingtianhong@...wei.com>,
David Woodhouse <dwmw@...zon.co.uk>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Dominik Brodowski <linux@...inikbrodowski.net>,
Juergen Gross <jgross@...e.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Dan Williams <dan.j.williams@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Mathias Krause <minipli@...glemail.com>,
Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
Kyle Huey <me@...ehuey.com>,
Dmitry Safonov <dsafonov@...tuozzo.com>,
Will Deacon <will.deacon@....com>,
Arnd Bergmann <arnd@...db.de>,
Florian Weimer <fweimer@...hat.com>,
Boris Lukashev <blukashev@...pervictus.com>,
x86@...nel.org,
linux-kernel@...r.kernel.org,
alex.popov@...ux.com
Subject: [PATCH v11 2/6] x86/entry: Add STACKLEAK erasing the kernel stack at the end of syscalls
The STACKLEAK feature erases the kernel stack before returning from
syscalls. That reduces the information which kernel stack leak bugs can
reveal and blocks some uninitialized stack variable attacks. Moreover,
STACKLEAK provides runtime checks for kernel stack overflow detection.
This commit introduces the architecture-specific code filling the used
part of the kernel stack with a poison value before returning to the
userspace. Full STACKLEAK feature also contains the gcc plugin which
comes in a separate commit.
The STACKLEAK feature is ported from grsecurity/PaX. More information at:
https://grsecurity.net/
https://pax.grsecurity.net/
This code is modified from Brad Spengler/PaX Team's code in the last
public patch of grsecurity/PaX based on our understanding of the code.
Changes or omissions from the original code are ours and don't reflect
the original grsecurity/PaX code.
Signed-off-by: Alexander Popov <alex.popov@...ux.com>
---
Documentation/x86/x86_64/mm.txt | 2 ++
arch/Kconfig | 27 ++++++++++++++++++++
arch/x86/Kconfig | 1 +
arch/x86/entry/Makefile | 3 +++
arch/x86/entry/calling.h | 14 +++++++++++
arch/x86/entry/entry_32.S | 7 ++++++
arch/x86/entry/entry_64.S | 3 +++
arch/x86/entry/entry_64_compat.S | 5 ++++
arch/x86/entry/erase.c | 54 ++++++++++++++++++++++++++++++++++++++++
arch/x86/include/asm/processor.h | 4 +++
arch/x86/kernel/process_32.c | 5 ++++
arch/x86/kernel/process_64.c | 5 ++++
include/linux/compiler.h | 4 +++
13 files changed, 134 insertions(+)
create mode 100644 arch/x86/entry/erase.c
diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt
index ea91cb6..21ee7c5 100644
--- a/Documentation/x86/x86_64/mm.txt
+++ b/Documentation/x86/x86_64/mm.txt
@@ -24,6 +24,7 @@ ffffffffa0000000 - [fixmap start] (~1526 MB) module mapping space (variable)
[fixmap start] - ffffffffff5fffff kernel-internal fixmap range
ffffffffff600000 - ffffffffff600fff (=4 kB) legacy vsyscall ABI
ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole
+STACKLEAK_POISON value in this last hole: ffffffffffff4111
Virtual memory map with 5 level page tables:
@@ -50,6 +51,7 @@ ffffffffa0000000 - fffffffffeffffff (1520 MB) module mapping space
[fixmap start] - ffffffffff5fffff kernel-internal fixmap range
ffffffffff600000 - ffffffffff600fff (=4 kB) legacy vsyscall ABI
ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole
+STACKLEAK_POISON value in this last hole: ffffffffffff4111
Architecture defines a 64-bit virtual address. Implementations can support
less. Currently supported are 48- and 57-bit virtual addresses. Bits 63
diff --git a/arch/Kconfig b/arch/Kconfig
index 76c0b54..368e2fb 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -401,6 +401,13 @@ config SECCOMP_FILTER
See Documentation/prctl/seccomp_filter.txt for details.
+config HAVE_ARCH_STACKLEAK
+ bool
+ help
+ An architecture should select this if it has the code which
+ fills the used part of the kernel stack with the STACKLEAK_POISON
+ value before returning from system calls.
+
config HAVE_GCC_PLUGINS
bool
help
@@ -531,6 +538,26 @@ config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE
in structures. This reduces the performance hit of RANDSTRUCT
at the cost of weakened randomization.
+config GCC_PLUGIN_STACKLEAK
+ bool "Erase the kernel stack before returning from syscalls"
+ depends on GCC_PLUGINS
+ depends on HAVE_ARCH_STACKLEAK
+ help
+ This option makes the kernel erase the kernel stack before it
+ returns from a system call. That reduces the information which
+ kernel stack leak bugs can reveal and blocks some uninitialized
+ stack variable attacks. This option also provides runtime checks
+ for kernel stack overflow detection.
+
+ The tradeoff is the performance impact: on a single CPU system kernel
+ compilation sees a 1% slowdown, other systems and workloads may vary
+ and you are advised to test this feature on your expected workload
+ before deploying it.
+
+ This plugin was ported from grsecurity/PaX. More information at:
+ * https://grsecurity.net/
+ * https://pax.grsecurity.net/
+
config HAVE_CC_STACKPROTECTOR
bool
help
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0fa71a7..e700879 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -119,6 +119,7 @@ config X86
select HAVE_ARCH_COMPAT_MMAP_BASES if MMU && COMPAT
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_THREAD_STRUCT_WHITELIST
+ select HAVE_ARCH_STACKLEAK
select HAVE_ARCH_TRACEHOOK
select HAVE_ARCH_TRANSPARENT_HUGEPAGE
select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64
diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile
index 06fc70c..abe4d92 100644
--- a/arch/x86/entry/Makefile
+++ b/arch/x86/entry/Makefile
@@ -15,3 +15,6 @@ obj-y += vsyscall/
obj-$(CONFIG_IA32_EMULATION) += entry_64_compat.o syscall_32.o
+obj-$(CONFIG_GCC_PLUGIN_STACKLEAK) += erase.o
+KASAN_SANITIZE_erase.o := n
+
diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index be63330..a555712 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -327,8 +327,22 @@ For 32-bit we have the following conventions - kernel is built with
#endif
+.macro ERASE_KSTACK_NOCLOBBER
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ PUSH_AND_CLEAR_REGS
+ call erase_kstack
+ POP_REGS
+#endif
+.endm
+
#endif /* CONFIG_X86_64 */
+.macro ERASE_KSTACK
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ call erase_kstack
+#endif
+.endm
+
/*
* This does 'call enter_from_user_mode' unless we can avoid it based on
* kernel config or using the static jump infrastructure.
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 6ad064c..733088e 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -46,6 +46,8 @@
#include <asm/frame.h>
#include <asm/nospec-branch.h>
+#include "calling.h"
+
.section .entry.text, "ax"
/*
@@ -298,6 +300,7 @@ ENTRY(ret_from_fork)
/* When we fork, we trace the syscall return in the child, too. */
movl %esp, %eax
call syscall_return_slowpath
+ ERASE_KSTACK
jmp restore_all
/* kernel thread */
@@ -458,6 +461,8 @@ ENTRY(entry_SYSENTER_32)
ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
"jmp .Lsyscall_32_done", X86_FEATURE_XENPV
+ ERASE_KSTACK
+
/* Opportunistic SYSEXIT */
TRACE_IRQS_ON /* User mode traces as IRQs on. */
movl PT_EIP(%esp), %edx /* pt_regs->ip */
@@ -544,6 +549,8 @@ ENTRY(entry_INT80_32)
call do_int80_syscall_32
.Lsyscall_32_done:
+ ERASE_KSTACK
+
restore_all:
TRACE_IRQS_IRET
.Lrestore_all_notrace:
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 18ed349..e267899 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -323,6 +323,8 @@ syscall_return_via_sysret:
* We are on the trampoline stack. All regs except RDI are live.
* We can do future final exit work right here.
*/
+ ERASE_KSTACK_NOCLOBBER
+
SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
popq %rdi
@@ -681,6 +683,7 @@ GLOBAL(swapgs_restore_regs_and_return_to_usermode)
* We are on the trampoline stack. All regs except RDI are live.
* We can do future final exit work right here.
*/
+ ERASE_KSTACK_NOCLOBBER
SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 08425c4..03d03d4 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -258,6 +258,11 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe)
/* Opportunistic SYSRET */
sysret32_from_system_call:
+ /*
+ * We are not going to return to the userspace from the trampoline
+ * stack. So let's erase the thread stack right now.
+ */
+ ERASE_KSTACK
TRACE_IRQS_ON /* User mode traces as IRQs on. */
movq RBX(%rsp), %rbx /* pt_regs->rbx */
movq RBP(%rsp), %rbp /* pt_regs->rbp */
diff --git a/arch/x86/entry/erase.c b/arch/x86/entry/erase.c
new file mode 100644
index 0000000..4892335
--- /dev/null
+++ b/arch/x86/entry/erase.c
@@ -0,0 +1,54 @@
+#include <linux/bug.h>
+#include <linux/sched.h>
+#include <asm/current.h>
+#include <asm/linkage.h>
+#include <asm/processor.h>
+
+asmlinkage void erase_kstack(void)
+{
+ register unsigned long p = current->thread.lowest_stack;
+ register unsigned long boundary = p & ~(THREAD_SIZE - 1);
+ unsigned long poison = 0;
+ const unsigned long check_depth = STACKLEAK_POISON_CHECK_DEPTH /
+ sizeof(unsigned long);
+
+ /*
+ * Let's search for the poison value in the stack.
+ * Start from the lowest_stack and go to the bottom.
+ */
+ while (p > boundary && poison <= check_depth) {
+ if (*(unsigned long *)p == STACKLEAK_POISON)
+ poison++;
+ else
+ poison = 0;
+
+ p -= sizeof(unsigned long);
+ }
+
+ /*
+ * One long int at the bottom of the thread stack is reserved and
+ * should not be poisoned (see CONFIG_SCHED_STACK_END_CHECK).
+ */
+ if (p == boundary)
+ p += sizeof(unsigned long);
+
+ /*
+ * So let's write the poison value to the kernel stack.
+ * Start from the address in p and move up till the new boundary.
+ */
+ if (on_thread_stack())
+ boundary = current_stack_pointer;
+ else
+ boundary = current_top_of_stack();
+
+ BUG_ON(boundary - p >= THREAD_SIZE);
+
+ while (p < boundary) {
+ *(unsigned long *)p = STACKLEAK_POISON;
+ p += sizeof(unsigned long);
+ }
+
+ /* Reset the lowest_stack value for the next syscall */
+ current->thread.lowest_stack = current_top_of_stack() - 256;
+}
+
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index b0ccd48..0c87813 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -494,6 +494,10 @@ struct thread_struct {
mm_segment_t addr_limit;
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ unsigned long lowest_stack;
+#endif
+
unsigned int sig_on_uaccess_err:1;
unsigned int uaccess_err:1; /* uaccess failed */
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 5224c60..1b0892e 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -136,6 +136,11 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
p->thread.sp0 = (unsigned long) (childregs+1);
memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ p->thread.lowest_stack = (unsigned long)task_stack_page(p) +
+ sizeof(unsigned long);
+#endif
+
if (unlikely(p->flags & PF_KTHREAD)) {
/* kernel thread */
memset(childregs, 0, sizeof(struct pt_regs));
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 9eb448c..82122af 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -281,6 +281,11 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
p->thread.sp = (unsigned long) fork_frame;
p->thread.io_bitmap_ptr = NULL;
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ p->thread.lowest_stack = (unsigned long)task_stack_page(p) +
+ sizeof(unsigned long);
+#endif
+
savesegment(gs, p->thread.gsindex);
p->thread.gsbase = p->thread.gsindex ? 0 : me->thread.gsbase;
savesegment(fs, p->thread.fsindex);
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index ab4711c..341b6cf8 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -342,4 +342,8 @@ unsigned long read_word_at_a_time(const void *addr)
compiletime_assert(__native_word(t), \
"Need native word sized stores/loads for atomicity.")
+/* Poison value points to the unused hole in the virtual memory map */
+#define STACKLEAK_POISON -0xBEEF
+#define STACKLEAK_POISON_CHECK_DEPTH 128
+
#endif /* __LINUX_COMPILER_H */
--
2.7.4
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