[PATCH 2/2] arm64: Clear the stack
From: Laura Abbott
Date: Tue Feb 20 2018 - 20:13:36 EST
Implementation of stackleak based heavily on the x86 version
Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/processor.h | 6 ++
arch/arm64/kernel/asm-offsets.c | 3 +
arch/arm64/kernel/entry.S | 108 ++++++++++++++++++++++++++++++++++
arch/arm64/kernel/process.c | 16 +++++
drivers/firmware/efi/libstub/Makefile | 3 +-
scripts/Makefile.gcc-plugins | 5 +-
7 files changed, 140 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7381eeb7ef8e..dcadcae674a7 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 fce604e3e599..4b309101ac83 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -114,6 +114,12 @@ 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
};
/*
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 1303e04110cd..b5c6100e8b14 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -45,6 +45,9 @@ int main(void)
DEFINE(TSK_TI_TTBR0, offsetof(struct task_struct, thread_info.ttbr0));
#endif
DEFINE(TSK_STACK, offsetof(struct task_struct, stack));
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ DEFINE(TSK_TI_LOWEST_STACK, offsetof(struct task_struct, thread.lowest_stack));
+#endif
BLANK();
DEFINE(THREAD_CPU_CONTEXT, offsetof(struct task_struct, thread.cpu_context));
BLANK();
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index ec2ee720e33e..b909b436293a 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.
*/
@@ -901,6 +906,7 @@ work_pending:
*/
ret_to_user:
disable_daif
+ erase_kstack
ldr x1, [tsk, #TSK_TI_FLAGS]
and x2, x1, #_TIF_WORK_MASK
cbnz x2, work_pending
@@ -1337,3 +1343,105 @@ alternative_else_nop_endif
ENDPROC(__sdei_asm_handler)
NOKPROBE(__sdei_asm_handler)
#endif /* CONFIG_ARM_SDE_INTERFACE */
+
+/*
+ * This is what the stack looks like
+ *
+ * +---+ <- task_stack_page(p) + THREAD_SIZE
+ * | |
+ * +---+ <- task_stack_page(p) + THREAD_START_SP
+ * | |
+ * | |
+ * +---+ <- task_pt_regs(p)
+ * | |
+ * | |
+ * | | <- current_sp
+ * ~~~~~
+ *
+ * ~~~~~
+ * | | <- lowest_stack
+ * | |
+ * | |
+ * +---+ <- task_stack_page(p)
+ *
+ * This function is desgned to poison the memory between the lowest_stack
+ * and the current stack pointer. After clearing the stack, the lowest
+ * stack is reset.
+ */
+
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+ENTRY(__erase_kstack)
+ mov x10, x0 // save x0 for the fast path
+
+ get_thread_info x0
+ ldr x1, [x0, #TSK_TI_LOWEST_STACK]
+
+ /* get the number of bytes to check for lowest stack */
+ mov x3, x1
+ and x3, x3, #THREAD_SIZE - 1
+ lsr x3, x3, #3
+
+ /* generate addresses from the bottom of the stack */
+ mov x4, sp
+ movn x2, #THREAD_SIZE - 1
+ and x1, x4, x2
+
+ mov x2, #STACKLEAK_POISON
+
+ mov x5, #0
+1:
+ /*
+ * As borrowed from the x86 logic, start from the lowest_stack
+ * and go to the bottom to find the poison value.
+ * The check of 16 is to hopefully avoid false positives.
+ */
+ cbz x3, 4f
+ ldr x4, [x1, x3, lsl #3]
+ cmp x4, x2
+ csinc x5, xzr, x5, ne
+ tbnz x5, #STACKLEAK_POISON_CHECK_DEPTH/4, 4f // found 16 poisons?
+ sub x3, x3, #1
+ b 1b
+
+4:
+ /* total number of bytes to poison */
+ add x5, x1, x3, lsl #3
+ mov x4, sp
+ sub x8, x4, x5
+
+ cmp x8, #THREAD_SIZE // sanity check the range
+ b.lo 5f
+ ASM_BUG()
+
+5:
+ /*
+ * We may have hit a path where the stack did not get used,
+ * no need to do anything here
+ */
+ cbz x8, 7f
+
+ sub x8, x8, #1 // don't poison the current stack pointer
+
+ lsr x8, x8, #3
+ add x3, x3, x8
+
+ /*
+ * The logic of this loop ensures the last stack word isn't
+ * ovewritten.
+ */
+6:
+ cbz x8, 7f
+ str x2, [x1, x3, lsl #3]
+ sub x3, x3, #1
+ sub x8, x8, #1
+ b 6b
+
+ /* Reset the lowest stack to the top of the stack */
+7:
+ mov x1, sp
+ str x1, [x0, #TSK_TI_LOWEST_STACK]
+
+ mov x0, x10
+ ret
+ENDPROC(__erase_kstack)
+#endif
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index ad8aeb098b31..fd0528db6772 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -357,6 +357,9 @@ 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;
@@ -486,3 +489,16 @@ 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 7b3ba40f0745..35ebbc1b17ff 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