On i386, 8 bytes are reserved above the user ptregs frame. The area is unused, but "necessary to guarantee that the entire "struct pt_regs" is accessible even if the CPU haven't stored the SS/ESP registers on the stack (interrupt gate does not save these registers when switching to the same priv ring)."
Use KERNEL_STACK_OFFSET to make the size of this area configurable and remove the difference between the sp0 setting in the tss and the percpu variable kernel_stack. For i386, KERNEL_STACK_OFFSET must be at least 8 bytes for the reason mentioned above and must be a multiple of 4 bytes, the minimal stack alignment. Signed-off-by: Alexander van Heukelum <[email protected]> --- arch/x86/include/asm/processor.h | 32 +++++++------------------------- arch/x86/include/asm/thread_info.h | 10 ++++++---- arch/x86/kernel/entry_32.S | 5 +++-- 3 files changed, 16 insertions(+), 31 deletions(-) diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 97117d1..f424e5f 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -842,7 +842,8 @@ static inline void spin_lock_prefetch(const void *x) #define STACK_TOP_MAX STACK_TOP #define INIT_THREAD { \ - .sp0 = sizeof(init_stack) + (long)&init_stack, \ + .sp0 = sizeof(init_stack) + (long)&init_stack \ + - KERNEL_STACK_OFFSET, \ .vm86_info = NULL, \ .sysenter_cs = __KERNEL_CS, \ .io_bitmap_ptr = NULL, \ @@ -856,7 +857,8 @@ static inline void spin_lock_prefetch(const void *x) */ #define INIT_TSS { \ .x86_tss = { \ - .sp0 = sizeof(init_stack) + (long)&init_stack, \ + .sp0 = sizeof(init_stack) + (long)&init_stack \ + - KERNEL_STACK_OFFSET, \ .ss0 = __KERNEL_DS, \ .ss1 = __KERNEL_CS, \ .io_bitmap_base = INVALID_IO_BITMAP_OFFSET, \ @@ -866,29 +868,9 @@ static inline void spin_lock_prefetch(const void *x) extern unsigned long thread_saved_pc(struct task_struct *tsk); -#define THREAD_SIZE_LONGS (THREAD_SIZE/sizeof(unsigned long)) -#define KSTK_TOP(info) \ -({ \ - unsigned long *__ptr = (unsigned long *)(info); \ - (unsigned long)(&__ptr[THREAD_SIZE_LONGS]); \ -}) - -/* - * The below -8 is to reserve 8 bytes on top of the ring0 stack. - * This is necessary to guarantee that the entire "struct pt_regs" - * is accessible even if the CPU haven't stored the SS/ESP registers - * on the stack (interrupt gate does not save these registers - * when switching to the same priv ring). - * Therefore beware: accessing the ss/esp fields of the - * "struct pt_regs" is possible, but they may contain the - * completely wrong values. - */ -#define task_pt_regs(task) \ -({ \ - struct pt_regs *__regs__; \ - __regs__ = (struct pt_regs *)(KSTK_TOP(task_stack_page(task))-8); \ - __regs__ - 1; \ -}) +#define task_pt_regs(task) \ + ((struct pt_regs *)((unsigned long)task_stack_page(task) + \ + THREAD_SIZE - KERNEL_STACK_OFFSET) - 1) #define KSTK_ESP(task) (task_pt_regs(task)->sp) diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h index 9f0c47f..36b8a10 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -153,14 +153,16 @@ struct thread_info { /* * Amount of reserved space between the top of the kernel stack page and the * user ptregs frame. + * On i386, this is necessary to guarantee that the entire "struct pt_regs" + * is accessible even if the CPU hasn't stored the SS/ESP registers on the + * stack (an interrupt gate does not save these registers when switching to + * the same priv ring). Therefore beware: accessing the ss/esp fields of the + * "struct pt_regs" is possible, but they may contain the completely wrong + * values. * On x86_64, KERNEL_STACK_OFFSET must be set to a multiple of 16 bytes due * to its automatic stack alignment for interrupts, traps, and exceptions. */ -#ifdef CONFIG_X86_32 -#define KERNEL_STACK_OFFSET (5*(BITS_PER_LONG/8)) -#else #define KERNEL_STACK_OFFSET (2*(BITS_PER_LONG/8)) -#endif /* * macros/functions for gaining access to the thread information structure diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S index 000d419..e94b994 100644 --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -396,9 +396,10 @@ sysenter_past_esp: /* * Push current_thread_info()->sysenter_return to the stack. * A tiny bit of offset fixup is necessary - 4*4 means the 4 words - * pushed above; +8 corresponds to copy_thread's esp0 setting. + * pushed above; KERNEL_STACK_OFFSET corresponds to copy_thread's + * esp0 setting. */ - pushl_cfi ((TI_sysenter_return)-THREAD_SIZE+8+4*4)(%esp) + pushl_cfi ((TI_sysenter_return)-THREAD_SIZE+KERNEL_STACK_OFFSET+4*4)(%esp) CFI_REL_OFFSET eip, 0 pushl_cfi %eax -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
