[PATCH 2/2] arm64: Clear the stack
Laura Abbott
labbott at redhat.com
Wed May 2 13:33:26 PDT 2018
Implementation of stackleak based heavily on the x86 version
Signed-off-by: Laura Abbott <labbott at redhat.com>
---
Now written in C instead of a bunch of assembly.
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/processor.h | 6 ++++
arch/arm64/kernel/Makefile | 3 ++
arch/arm64/kernel/entry.S | 6 ++++
arch/arm64/kernel/erase.c | 55 +++++++++++++++++++++++++++++++++++
arch/arm64/kernel/process.c | 16 ++++++++++
drivers/firmware/efi/libstub/Makefile | 3 +-
scripts/Makefile.gcc-plugins | 5 +++-
8 files changed, 93 insertions(+), 2 deletions(-)
create mode 100644 arch/arm64/kernel/erase.c
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..d31ab80ff647 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -124,6 +124,12 @@ struct thread_struct {
unsigned long fault_address; /* fault info */
unsigned long fault_code; /* ESR_EL1 value */
struct debug_info debug; /* debugging */
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ unsigned long lowest_stack;
+#ifdef CONFIG_STACKLEAK_METRICS
+ unsigned long prev_lowest_stack;
+#endif
+#endif
};
static inline void arch_thread_struct_whitelist(unsigned long *offset,
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index bf825f38d206..0ceea613c65b 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -55,6 +55,9 @@ arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o
arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o
+arm64-obj-$(CONFIG_GCC_PLUGIN_STACKLEAK) += erase.o
+KASAN_SANITIZE_erase.o := n
+
obj-y += $(arm64-obj-y) vdso/ probes/
obj-m += $(arm64-obj-m)
head-y := head.o
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index ec2ee720e33e..3144f1ebdc18 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 ERASE_KSTACK
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ bl erase_kstack
+#endif
+ .endm
/*
* Exception vectors.
*/
@@ -906,6 +911,7 @@ ret_to_user:
cbnz x2, work_pending
finish_ret_to_user:
enable_step_tsk x1, x2
+ ERASE_KSTACK
kernel_exit 0
ENDPROC(ret_to_user)
diff --git a/arch/arm64/kernel/erase.c b/arch/arm64/kernel/erase.c
new file mode 100644
index 000000000000..b8b5648d893b
--- /dev/null
+++ b/arch/arm64/kernel/erase.c
@@ -0,0 +1,55 @@
+#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)
+{
+ unsigned long p = current->thread.lowest_stack;
+ 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);
+
+#ifdef CONFIG_STACKLEAK_METRICS
+ current->thread.prev_lowest_stack = p;
+#endif
+
+ /*
+ * So let's write the poison value to the kernel stack.
+ * Start from the address in p and move up till the new boundary.
+ */
+ boundary = current_stack_pointer;
+
+ 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_stack_pointer;
+}
+
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index f08a2ed9db0d..156fa0a0da19 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -364,6 +364,9 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
p->thread.cpu_context.pc = (unsigned long)ret_from_fork;
p->thread.cpu_context.sp = (unsigned long)childregs;
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ p->thread.lowest_stack = (unsigned long)task_stack_page(p);
+#endif
ptrace_hw_copy_thread(p);
return 0;
@@ -493,3 +496,16 @@ void arch_setup_new_exec(void)
{
current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
}
+
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+void __used check_alloca(unsigned long size)
+{
+ unsigned long sp, stack_left;
+
+ sp = current_stack_pointer;
+
+ stack_left = sp & (THREAD_SIZE - 1);
+ BUG_ON(stack_left < 256 || size >= stack_left - 256);
+}
+EXPORT_SYMBOL(check_alloca);
+#endif
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) \
+ $(DISABLE_STACKLEAK_PLUGIN)
GCOV_PROFILE := n
KASAN_SANITIZE := n
diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index 8d6070fc538f..6cc0e35d3324 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -37,11 +37,14 @@ ifdef CONFIG_GCC_PLUGINS
gcc-plugin-$(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.
--
2.14.3
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