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

Since checkin ebba638ae723d8a8fc2f7abce5ec18b688b791d7 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>

1 files changed, 13 insertions, 17 deletions

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index fc293dc8dc35..767d6c43de37 100644
--- a/arch/x86/kernel/head_32.S
+++ b/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"