x86/entry: Clean up the SYSENTER_stack code

The existing code was a mess, mainly because C arrays are nasty.  Turn
SYSENTER_stack into a struct, add a helper to find it, and do all the
obvious cleanups this enables.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bpetkov@suse.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Link: https://lkml.kernel.org/r/20171204150606.653244723@linutronix.deSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/entry/entry_32.S

@@ -942,7 +942,7 @@ ENTRY(debug)
 
 	/* Are we currently on the SYSENTER stack? */
 	movl	PER_CPU_VAR(cpu_entry_area), %ecx
-	addl	$CPU_ENTRY_AREA_tss + CPU_TSS_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx
+	addl	$CPU_ENTRY_AREA_tss + TSS_STRUCT_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx
 	subl	%eax, %ecx	/* ecx = (end of SYSENTER_stack) - esp */
 	cmpl	$SIZEOF_SYSENTER_stack, %ecx
 	jb	.Ldebug_from_sysenter_stack
@@ -986,7 +986,7 @@ ENTRY(nmi)
 
 	/* Are we currently on the SYSENTER stack? */
 	movl	PER_CPU_VAR(cpu_entry_area), %ecx
-	addl	$CPU_ENTRY_AREA_tss + CPU_TSS_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx
+	addl	$CPU_ENTRY_AREA_tss + TSS_STRUCT_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx
 	subl	%eax, %ecx	/* ecx = (end of SYSENTER_stack) - esp */
 	cmpl	$SIZEOF_SYSENTER_stack, %ecx
 	jb	.Lnmi_from_sysenter_stack

arch/x86/entry/entry_64.S

@@ -154,7 +154,7 @@ END(native_usergs_sysret64)
 	_entry_trampoline - CPU_ENTRY_AREA_entry_trampoline(%rip)
 
 /* The top word of the SYSENTER stack is hot and is usable as scratch space. */
-#define RSP_SCRATCH	CPU_ENTRY_AREA_tss + CPU_TSS_SYSENTER_stack + \
+#define RSP_SCRATCH	CPU_ENTRY_AREA_tss + TSS_STRUCT_SYSENTER_stack + \
 			SIZEOF_SYSENTER_stack - 8 + CPU_ENTRY_AREA
 
 ENTRY(entry_SYSCALL_64_trampoline)

arch/x86/include/asm/fixmap.h

@@ -245,5 +245,10 @@ static inline struct cpu_entry_area *get_cpu_entry_area(int cpu)
 	return (struct cpu_entry_area *)__fix_to_virt(__get_cpu_entry_area_page_index(cpu, 0));
 }
 
+static inline struct SYSENTER_stack *cpu_SYSENTER_stack(int cpu)
+{
+	return &get_cpu_entry_area(cpu)->tss.SYSENTER_stack;
+}
+
 #endif /* !__ASSEMBLY__ */
 #endif /* _ASM_X86_FIXMAP_H */

arch/x86/include/asm/processor.h

@@ -336,12 +336,16 @@ struct x86_hw_tss {
 #define IO_BITMAP_OFFSET		(offsetof(struct tss_struct, io_bitmap) - offsetof(struct tss_struct, x86_tss))
 #define INVALID_IO_BITMAP_OFFSET	0x8000
 
+struct SYSENTER_stack {
+	unsigned long		words[64];
+};
+
 struct tss_struct {
 	/*
 	 * Space for the temporary SYSENTER stack, used for SYSENTER
 	 * and the entry trampoline as well.
 	 */
-	unsigned long		SYSENTER_stack[64];
+	struct SYSENTER_stack	SYSENTER_stack;
 
 	/*
 	 * The fixed hardware portion.  This must not cross a page boundary

arch/x86/kernel/asm-offsets.c

@@ -94,10 +94,8 @@ void common(void) {
 	BLANK();
 	DEFINE(PTREGS_SIZE, sizeof(struct pt_regs));
 
-	/* Offset from cpu_tss to SYSENTER_stack */
-	OFFSET(CPU_TSS_SYSENTER_stack, tss_struct, SYSENTER_stack);
-	/* Size of SYSENTER_stack */
-	DEFINE(SIZEOF_SYSENTER_stack, sizeof(((struct tss_struct *)0)->SYSENTER_stack));
+	OFFSET(TSS_STRUCT_SYSENTER_stack, tss_struct, SYSENTER_stack);
+	DEFINE(SIZEOF_SYSENTER_stack, sizeof(struct SYSENTER_stack));
 
 	/* Layout info for cpu_entry_area */
 	OFFSET(CPU_ENTRY_AREA_tss, cpu_entry_area, tss);

arch/x86/kernel/cpu/common.c

@@ -1314,12 +1314,7 @@ void enable_sep_cpu(void)
 
 	tss->x86_tss.ss1 = __KERNEL_CS;
 	wrmsr(MSR_IA32_SYSENTER_CS, tss->x86_tss.ss1, 0);
-
-	wrmsr(MSR_IA32_SYSENTER_ESP,
-	      (unsigned long)&get_cpu_entry_area(cpu)->tss +
-	      offsetofend(struct tss_struct, SYSENTER_stack),
-	      0);
-
+	wrmsr(MSR_IA32_SYSENTER_ESP, (unsigned long)(cpu_SYSENTER_stack(cpu) + 1), 0);
 	wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long)entry_SYSENTER_32, 0);
 
 	put_cpu();
@@ -1436,9 +1431,7 @@ void syscall_init(void)
 	 * AMD doesn't allow SYSENTER in long mode (either 32- or 64-bit).
 	 */
 	wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)__KERNEL_CS);
-	wrmsrl_safe(MSR_IA32_SYSENTER_ESP,
-		    (unsigned long)&get_cpu_entry_area(cpu)->tss +
-		    offsetofend(struct tss_struct, SYSENTER_stack));
+	wrmsrl_safe(MSR_IA32_SYSENTER_ESP, (unsigned long)(cpu_SYSENTER_stack(cpu) + 1));
 	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
 #else
 	wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret);
@@ -1653,8 +1646,7 @@ void cpu_init(void)
 	 */
 	set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
 	load_TR_desc();
-	load_sp0((unsigned long)&get_cpu_entry_area(cpu)->tss +
-		 offsetofend(struct tss_struct, SYSENTER_stack));
+	load_sp0((unsigned long)(cpu_SYSENTER_stack(cpu) + 1));
 
 	load_mm_ldt(&init_mm);
 

arch/x86/kernel/dumpstack.c

@@ -45,11 +45,10 @@ bool in_task_stack(unsigned long *stack, struct task_struct *task,
 
 bool in_sysenter_stack(unsigned long *stack, struct stack_info *info)
 {
-	int cpu = smp_processor_id();
-	struct tss_struct *tss = &get_cpu_entry_area(cpu)->tss;
+	struct SYSENTER_stack *ss = cpu_SYSENTER_stack(smp_processor_id());
 
-	void *begin = &tss->SYSENTER_stack;
-	void *end = (void *)&tss->SYSENTER_stack + sizeof(tss->SYSENTER_stack);
+	void *begin = ss;
+	void *end = ss + 1;
 
 	if ((void *)stack < begin || (void *)stack >= end)
 		return false;