Re: [PATCH] arm64: Clear the stack
From: Laura Abbott
Date: Mon Jul 02 2018 - 14:48:14 EST
On 07/02/2018 06:02 AM, Alexander Popov wrote:
Hello Laura,
Thanks for your work!
Please see my comments below.
On 29.06.2018 22:05, Laura Abbott wrote:
Implementation of stackleak based heavily on the x86 version
Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
---
Changes since last time:
- Minor name change in entry.S
- Converted to use the generic interfaces so there's minimal additions.
- Added the fast syscall path.
- Addition of on_thread_stack and current_top_of_stack
- Disable stackleak on hyp per suggestion
- Added a define for check_alloca. I'm still not sure about keeping it
since the x86 version got reworked?
I've mostly kept this as one patch with a minimal commit text. I can
split it up and elaborate more before final merging.
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/processor.h | 9 +++++++++
arch/arm64/kernel/entry.S | 7 +++++++
arch/arm64/kernel/process.c | 16 ++++++++++++++++
arch/arm64/kvm/hyp/Makefile | 3 ++-
drivers/firmware/efi/libstub/Makefile | 3 ++-
include/linux/stackleak.h | 1 +
scripts/Makefile.gcc-plugins | 5 ++++-
8 files changed, 42 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index eb2cf4938f6d..b0221db95dc9 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -92,6 +92,7 @@ config ARM64
select HAVE_ARCH_MMAP_RND_BITS
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
select HAVE_ARCH_SECCOMP_FILTER
+ select HAVE_ARCH_STACKLEAK
select HAVE_ARCH_THREAD_STRUCT_WHITELIST
select HAVE_ARCH_TRACEHOOK
select HAVE_ARCH_TRANSPARENT_HUGEPAGE
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 767598932549..73914fd7e142 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -248,5 +248,14 @@ void cpu_clear_disr(const struct arm64_cpu_capabilities *__unused);
#define SVE_SET_VL(arg) sve_set_current_vl(arg)
#define SVE_GET_VL() sve_get_current_vl()
+/*
+ * For stackleak
May I ask you to call it STACKLEAK here and in other places for easier grep?
Sure
+ *
+ * These need to be macros because otherwise we get stuck in a nightmare
+ * of header definitions for the use of task_stack_page.
+ */
+#define current_top_of_stack() (task_stack_page(current) + THREAD_SIZE)
+#define on_thread_stack() (on_task_stack(current, current_stack_pointer))
+
#endif /* __ASSEMBLY__ */
#endif /* __ASM_PROCESSOR_H */
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index ec2ee720e33e..31c9da7d401e 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -401,6 +401,11 @@ tsk .req x28 // current thread_info
.text
+ .macro stackleak_erase
Could you rename the macro to STACKLEAK_ERASE for similarity with x86?
Mark Rutland had previously asked for this to be lowercase.
I really don't care one way or the other so I'll defer to
someone else to have the final word.
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ bl stackleak_erase_kstack
+#endif
+ .endm
/*
* Exception vectors.
*/
@@ -880,6 +885,7 @@ ret_fast_syscall:
and x2, x1, #_TIF_WORK_MASK
cbnz x2, work_pending
enable_step_tsk x1, x2
+ stackleak_erase
kernel_exit 0
ret_fast_syscall_trace:
enable_daif
@@ -906,6 +912,7 @@ ret_to_user:
cbnz x2, work_pending
finish_ret_to_user:
enable_step_tsk x1, x2
+ stackleak_erase
kernel_exit 0
ENDPROC(ret_to_user)
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index f08a2ed9db0d..9f0f135f8b66 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -493,3 +493,19 @@ void arch_setup_new_exec(void)
{
current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
}
+
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+#define MIN_STACK_LEFT 256
+
+void __used stackleak_check_alloca(unsigned long size)
+{
+ unsigned long sp, stack_left;
+
+ sp = current_stack_pointer;
+
+ stack_left = sp & (THREAD_SIZE - 1);
+ BUG_ON(stack_left < MIN_STACK_LEFT ||
+ size >= stack_left - MIN_STACK_LEFT);
+}
+EXPORT_SYMBOL(stackleak_check_alloca);
+#endif
This code should be updated.
You may remember the troubles I had with MIN_STACK_LEFT:
http://openwall.com/lists/kernel-hardening/2018/05/11/12
Please see that thread where Mark Rutland and I worked out the solution.
Ah yeah, I missed the details in that thread. Thanks for
that pointer.
By the way, different stacks on x86_64 have different sizes. Is it false for arm64?
Currently everything except the overflow stack looks to be
the same size but there's also another stack I missed. It might
be cleaner just to use on_accessible_stack and then another
function to get the top of stack. This also might just be
reimplementing what x86 already has? (Mark, Ard?)
Thanks,
Laura
diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index 4313f7475333..2fabc2dc1966 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile
@@ -3,7 +3,8 @@
# Makefile for Kernel-based Virtual Machine module, HYP part
#
-ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING
+ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING \
+ $(DISABLE_STACKLEAK_PLUGIN)
KVM=../../../../virt/kvm
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index a34e9290a699..25dd2a14560d 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -20,7 +20,8 @@ cflags-$(CONFIG_EFI_ARMSTUB) += -I$(srctree)/scripts/dtc/libfdt
KBUILD_CFLAGS := $(cflags-y) -DDISABLE_BRANCH_PROFILING \
-D__NO_FORTIFY \
$(call cc-option,-ffreestanding) \
- $(call cc-option,-fno-stack-protector)
+ $(call cc-option,-fno-stack-protector) \
+ $(DISABLE_STACKLEAK_PLUGIN)
GCOV_PROFILE := n
KASAN_SANITIZE := n
diff --git a/include/linux/stackleak.h b/include/linux/stackleak.h
index e2da99b3a191..00d62b302efb 100644
--- a/include/linux/stackleak.h
+++ b/include/linux/stackleak.h
@@ -5,6 +5,7 @@
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
+#include <asm/stacktrace.h>
/*
* Check that the poison value points to the unused hole in the
* virtual memory map for your platform.
diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index a535742a1c06..972ce4ca7f6a 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -37,11 +37,14 @@ ifdef CONFIG_GCC_PLUGINS
gcc-plugin-$(CONFIG_GCC_PLUGIN_STACKLEAK) += stackleak_plugin.so
gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STACKLEAK) += -DSTACKLEAK_PLUGIN -fplugin-arg-stackleak_plugin-track-min-size=$(CONFIG_STACKLEAK_TRACK_MIN_SIZE)
+ ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ DISABLE_STACKLEAK_PLUGIN += -fplugin-arg-stackleak_plugin-disable
+ endif
GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))
export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN GCC_PLUGIN_SUBDIR
- export SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN
+ export SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN DISABLE_STACKLEAK_PLUGIN
ifneq ($(PLUGINCC),)
# SANCOV_PLUGIN can be only in CFLAGS_KCOV because avoid duplication.