x86-32: Make sure the stack is set up before we use it

Since checkin ebba638 we call
verify_cpu even in 32-bit mode.  Unfortunately, calling a function
means using the stack, and the stack pointer was not initialized in
the 32-bit setup code!  This code initializes the stack pointer, and
simplifies the interface slightly since it is easier to rely on just a
pointer value rather than a descriptor; we need to have different
values for the segment register anyway.

This retains start_stack as a virtual address, even though a physical
address would be more convenient for 32 bits; the 64-bit code wants
the other way around...

Reported-by: Matthieu Castet <castet.matthieu@free.fr>
LKML-Reference: <4D41E86D.8060205@free.fr>
Tested-by: Kees Cook <kees.cook@canonical.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/smp.h

@@ -40,10 +40,7 @@ DECLARE_EARLY_PER_CPU(u16, x86_cpu_to_apicid);
 DECLARE_EARLY_PER_CPU(u16, x86_bios_cpu_apicid);
 
 /* Static state in head.S used to set up a CPU */
-extern struct {
-	void *sp;
-	unsigned short ss;
-} stack_start;
+extern unsigned long stack_start; /* Initial stack pointer address */
 
 struct smp_ops {
 	void (*smp_prepare_boot_cpu)(void);

arch/x86/kernel/acpi/sleep.c

@@ -100,7 +100,7 @@ int acpi_save_state_mem(void)
 #else /* CONFIG_64BIT */
 	header->trampoline_segment = setup_trampoline() >> 4;
 #ifdef CONFIG_SMP
-	stack_start.sp = temp_stack + sizeof(temp_stack);
+	stack_start = (unsigned long)temp_stack + sizeof(temp_stack);
 	early_gdt_descr.address =
 			(unsigned long)get_cpu_gdt_table(smp_processor_id());
 	initial_gs = per_cpu_offset(smp_processor_id());

arch/x86/kernel/head_32.S

@@ -85,6 +85,8 @@ RESERVE_BRK(pagetables, INIT_MAP_SIZE)
  */
 __HEAD
 ENTRY(startup_32)
+	movl pa(stack_start),%ecx
+
 	/* test KEEP_SEGMENTS flag to see if the bootloader is asking
 		us to not reload segments */
 	testb $(1<<6), BP_loadflags(%esi)
@@ -99,7 +101,9 @@ ENTRY(startup_32)
 	movl %eax,%es
 	movl %eax,%fs
 	movl %eax,%gs
+	movl %eax,%ss
 2:
+	leal -__PAGE_OFFSET(%ecx),%esp
 
 /*
  * Clear BSS first so that there are no surprises...
@@ -145,8 +149,6 @@ ENTRY(startup_32)
  * _brk_end is set up to point to the first "safe" location.
  * Mappings are created both at virtual address 0 (identity mapping)
  * and PAGE_OFFSET for up to _end.
- *
- * Note that the stack is not yet set up!
  */
 #ifdef CONFIG_X86_PAE
 
@@ -282,6 +284,9 @@ ENTRY(startup_32_smp)
 	movl %eax,%es
 	movl %eax,%fs
 	movl %eax,%gs
+	movl pa(stack_start),%ecx
+	movl %eax,%ss
+	leal -__PAGE_OFFSET(%ecx),%esp
 #endif /* CONFIG_SMP */
 default_entry:
 
@@ -347,8 +352,8 @@ default_entry:
 	movl %eax,%cr0		/* ..and set paging (PG) bit */
 	ljmp $__BOOT_CS,$1f	/* Clear prefetch and normalize %eip */
 1:
-	/* Set up the stack pointer */
-	lss stack_start,%esp
+	/* Shift the stack pointer to a virtual address */
+	addl $__PAGE_OFFSET, %esp
 
 /*
  * Initialize eflags.  Some BIOS's leave bits like NT set.  This would
@@ -360,9 +365,7 @@ default_entry:
 
 #ifdef CONFIG_SMP
 	cmpb $0, ready
-	jz  1f				/* Initial CPU cleans BSS */
-	jmp checkCPUtype
-1:
+	jnz checkCPUtype
 #endif /* CONFIG_SMP */
 
 /*
@@ -470,14 +473,7 @@ is386:	movl $2,%ecx		# set MP
 
 	cld			# gcc2 wants the direction flag cleared at all times
 	pushl $0		# fake return address for unwinder
-#ifdef CONFIG_SMP
-	movb ready, %cl
 	movb $1, ready
-	cmpb $0,%cl		# the first CPU calls start_kernel
-	je   1f
-	movl (stack_start), %esp
-1:
-#endif /* CONFIG_SMP */
 	jmp *(initial_code)
 
 /*
@@ -670,15 +666,15 @@ ENTRY(initial_page_table)
 #endif
 
 .data
+.balign 4
 ENTRY(stack_start)
 	.long init_thread_union+THREAD_SIZE
-	.long __BOOT_DS
-
-ready:	.byte 0
 
 early_recursion_flag:
 	.long 0
 
+ready:	.byte 0
+
 int_msg:
 	.asciz "Unknown interrupt or fault at: %p %p %p\n"
 

arch/x86/kernel/smpboot.c

@@ -638,7 +638,7 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
 	 * target processor state.
 	 */
 	startup_ipi_hook(phys_apicid, (unsigned long) start_secondary,
-			 (unsigned long)stack_start.sp);
+			 stack_start);
 
 	/*
 	 * Run STARTUP IPI loop.
@@ -785,7 +785,7 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu)
 #endif
 	early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);
 	initial_code = (unsigned long)start_secondary;
-	stack_start.sp = (void *) c_idle.idle->thread.sp;
+	stack_start  = c_idle.idle->thread.sp;
 
 	/* start_ip had better be page-aligned! */
 	start_ip = setup_trampoline();