1 files changed, 95 insertions, 0 deletions
diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
new file mode 100644
index 000000000..24a8d6c4f
--- /dev/null
+++ b/arch/x86/include/asm/stackprotector.h
@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * GCC stack protector support.
+ *
+ * Stack protector works by putting predefined pattern at the start of
+ * the stack frame and verifying that it hasn't been overwritten when
+ * returning from the function.  The pattern is called stack canary
+ * and unfortunately gcc historically required it to be at a fixed offset
+ * from the percpu segment base.  On x86_64, the offset is 40 bytes.
+ *
+ * The same segment is shared by percpu area and stack canary.  On
+ * x86_64, percpu symbols are zero based and %gs (64-bit) points to the
+ * base of percpu area.  The first occupant of the percpu area is always
+ * fixed_percpu_data which contains stack_canary at the appropriate
+ * offset.  On x86_32, the stack canary is just a regular percpu
+ * variable.
+ *
+ * Putting percpu data in %fs on 32-bit is a minor optimization compared to
+ * using %gs.  Since 32-bit userspace normally has %fs == 0, we are likely
+ * to load 0 into %fs on exit to usermode, whereas with percpu data in
+ * %gs, we are likely to load a non-null %gs on return to user mode.
+ *
+ * Once we are willing to require GCC 8.1 or better for 64-bit stackprotector
+ * support, we can remove some of this complexity.
+ */
+
+#ifndef _ASM_STACKPROTECTOR_H
+#define _ASM_STACKPROTECTOR_H 1
+
+#ifdef CONFIG_STACKPROTECTOR
+
+#include <asm/tsc.h>
+#include <asm/processor.h>
+#include <asm/percpu.h>
+#include <asm/desc.h>
+
+#include <linux/random.h>
+#include <linux/sched.h>
+
+/*
+ * Initialize the stackprotector canary value.
+ *
+ * NOTE: this must only be called from functions that never return
+ * and it must always be inlined.
+ *
+ * In addition, it should be called from a compilation unit for which
+ * stack protector is disabled. Alternatively, the caller should not end
+ * with a function call which gets tail-call optimized as that would
+ * lead to checking a modified canary value.
+ */
+static __always_inline void boot_init_stack_canary(void)
+{
+	u64 canary;
+	u64 tsc;
+
+#ifdef CONFIG_X86_64
+	BUILD_BUG_ON(offsetof(struct fixed_percpu_data, stack_canary) != 40);
+#endif
+	/*
+	 * We both use the random pool and the current TSC as a source
+	 * of randomness. The TSC only matters for very early init,
+	 * there it already has some randomness on most systems. Later
+	 * on during the bootup the random pool has true entropy too.
+	 */
+	get_random_bytes(&canary, sizeof(canary));
+	tsc = rdtsc();
+	canary += tsc + (tsc << 32UL);
+	canary &= CANARY_MASK;
+
+	current->stack_canary = canary;
+#ifdef CONFIG_X86_64
+	this_cpu_write(fixed_percpu_data.stack_canary, canary);
+#else
+	this_cpu_write(__stack_chk_guard, canary);
+#endif
+}
+
+static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle)
+{
+#ifdef CONFIG_X86_64
+	per_cpu(fixed_percpu_data.stack_canary, cpu) = idle->stack_canary;
+#else
+	per_cpu(__stack_chk_guard, cpu) = idle->stack_canary;
+#endif
+}
+
+#else	/* STACKPROTECTOR */
+
+/* dummy boot_init_stack_canary() is defined in linux/stackprotector.h */
+
+static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle)
+{ }
+
+#endif	/* STACKPROTECTOR */
+#endif	/* _ASM_STACKPROTECTOR_H */