1 files changed, 21 insertions, 85 deletions

diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
index 6a998598f172..cd761b14eb02 100644
--- a/arch/x86/include/asm/stackprotector.h
+++ b/arch/x86/include/asm/stackprotector.h
@@ -1,121 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * GCC stack protector support.
  *
- * Stack protector works by putting predefined pattern at the start of
+ * Stack protector works by putting a 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 requires it to be at a fixed offset from %gs.
- * On x86_64, the offset is 40 bytes and on x86_32 20 bytes.  x86_64
- * and x86_32 use segment registers differently and thus handles this
- * requirement differently.
- *
- * On x86_64, %gs is shared by percpu area and stack canary.  All
- * percpu symbols are zero based and %gs points to the base of percpu
- * area.  The first occupant of the percpu area is always
- * irq_stack_union which contains stack_canary at offset 40.  Userland
- * %gs is always saved and restored on kernel entry and exit using
- * swapgs, so stack protector doesn't add any complexity there.
- *
- * On x86_32, it's slightly more complicated.  As in x86_64, %gs is
- * used for userland TLS.  Unfortunately, some processors are much
- * slower at loading segment registers with different value when
- * entering and leaving the kernel, so the kernel uses %fs for percpu
- * area and manages %gs lazily so that %gs is switched only when
- * necessary, usually during task switch.
- *
- * As gcc requires the stack canary at %gs:20, %gs can't be managed
- * lazily if stack protector is enabled, so the kernel saves and
- * restores userland %gs on kernel entry and exit.  This behavior is
- * controlled by CONFIG_X86_32_LAZY_GS and accessors are defined in
- * system.h to hide the details.
+ * returning from the function.  The pattern is called the stack canary
+ * and is a unique value for each task.
  */
 
 #ifndef _ASM_STACKPROTECTOR_H
 #define _ASM_STACKPROTECTOR_H 1
 
-#ifdef CONFIG_CC_STACKPROTECTOR
+#ifdef CONFIG_STACKPROTECTOR
 
 #include <asm/tsc.h>
 #include <asm/processor.h>
 #include <asm/percpu.h>
 #include <asm/desc.h>
-#include <linux/random.h>
 
-/*
- * 24 byte read-only segment initializer for stack canary.  Linker
- * can't handle the address bit shifting.  Address will be set in
- * head_32 for boot CPU and setup_per_cpu_areas() for others.
- */
-#define GDT_STACK_CANARY_INIT						\
-	[GDT_ENTRY_STACK_CANARY] = GDT_ENTRY_INIT(0x4090, 0, 0x18),
+#include <linux/sched.h>
+
+DECLARE_PER_CPU_CACHE_HOT(unsigned long, __stack_chk_guard);
 
 /*
  * Initialize the stackprotector canary value.
  *
- * NOTE: this must only be called from functions that never return,
+ * 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(union irq_stack_union, 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 = __native_read_tsc();
-	canary += tsc + (tsc << 32UL);
+	unsigned long canary = get_random_canary();
 
 	current->stack_canary = canary;
-#ifdef CONFIG_X86_64
-	this_cpu_write(irq_stack_union.stack_canary, canary);
-#else
-	this_cpu_write(stack_canary.canary, canary);
-#endif
+	this_cpu_write(__stack_chk_guard, canary);
 }
 
-static inline void setup_stack_canary_segment(int cpu)
+static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle)
 {
-#ifdef CONFIG_X86_32
-	unsigned long canary = (unsigned long)&per_cpu(stack_canary, cpu);
-	struct desc_struct *gdt_table = get_cpu_gdt_table(cpu);
-	struct desc_struct desc;
-
-	desc = gdt_table[GDT_ENTRY_STACK_CANARY];
-	set_desc_base(&desc, canary);
-	write_gdt_entry(gdt_table, GDT_ENTRY_STACK_CANARY, &desc, DESCTYPE_S);
-#endif
-}
-
-static inline void load_stack_canary_segment(void)
-{
-#ifdef CONFIG_X86_32
-	asm("mov %0, %%gs" : : "r" (__KERNEL_STACK_CANARY) : "memory");
-#endif
+	per_cpu(__stack_chk_guard, cpu) = idle->stack_canary;
 }
 
-#else	/* CC_STACKPROTECTOR */
-
-#define GDT_STACK_CANARY_INIT
+#else	/* STACKPROTECTOR */
 
 /* dummy boot_init_stack_canary() is defined in linux/stackprotector.h */
 
-static inline void setup_stack_canary_segment(int cpu)
+static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle)
 { }
 
-static inline void load_stack_canary_segment(void)
-{
-#ifdef CONFIG_X86_32
-	asm volatile ("mov %0, %%gs" : : "r" (0));
-#endif
-}
-
-#endif	/* CC_STACKPROTECTOR */
+#endif	/* STACKPROTECTOR */
 #endif	/* _ASM_STACKPROTECTOR_H */