On Tue, Mar 10, 2015 at 12:22 PM, Denys Vlasenko <[email protected]> wrote: > On 03/10/2015 07:05 PM, Andy Lutomirski wrote: >> x86_32, unlike x86_64, pads the top of the kernel stack. Document >> this padding and give it a name. >> >> This should make no change whatsoever to the compiled kernel image. >> It also doesn't fix any of the current bugs in this area. >> >> Signed-off-by: Andy Lutomirski <[email protected]> >> --- >> arch/x86/include/asm/processor.h | 3 ++- >> arch/x86/include/asm/thread_info.h | 30 ++++++++++++++++++++++++++++++ >> 2 files changed, 32 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/include/asm/processor.h >> b/arch/x86/include/asm/processor.h >> index 48a61c1c626e..88d9aa745898 100644 >> --- a/arch/x86/include/asm/processor.h >> +++ b/arch/x86/include/asm/processor.h >> @@ -849,7 +849,8 @@ extern unsigned long thread_saved_pc(struct task_struct >> *tsk); >> #define task_pt_regs(task) \ >> ({ \ >> struct pt_regs *__regs__; \ >> - __regs__ = (struct pt_regs *)(KSTK_TOP(task_stack_page(task))-8); \ >> + __regs__ = (struct pt_regs *)(KSTK_TOP(task_stack_page(task)) - \ >> + TOP_OF_KERNEL_STACK_PADDING); \ >> __regs__ - 1; \ >> }) > > The "magic 8" also hides here: > > /* > * 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. > */ > pushl_cfi ((TI_sysenter_return)-THREAD_SIZE+8+4*4)(%esp) > ^^^
I'll just put TOP_OF_KERNEL_STACK_PADDING there, too. --Andy > CFI_REL_OFFSET eip, 0 > > > It may make sense to mention TOP_OF_KERNEL_STACK_PADDING here > (there are no useful comments in copy_thread() anymore): > > movl PT_EFLAGS(%esp), %eax # mix EFLAGS, SS and CS > # Warning: PT_OLDSS(%esp) contains the wrong/random values if we > # are returning to the kernel. > # See comments in process.c:copy_thread() for details. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > maybe s/comments in process.c:copy_thread()/TOP_OF_KERNEL_STACK_PADDING/ ? > movb PT_OLDSS(%esp), %ah > movb PT_CS(%esp), %al > andl $(X86_EFLAGS_VM | (SEGMENT_TI_MASK << 8) | SEGMENT_RPL_MASK), > %eax > cmpl $((SEGMENT_LDT << 8) | USER_RPL), %eax > CFI_REMEMBER_STATE > -- Andy Lutomirski AMA Capital Management, LLC -- 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/
