lkml.org 
[lkml]   [2017]   [Nov]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 13/43] x86/asm/64: Use a percpu trampoline stack for IDT entries

* Borislav Petkov <bp@alien8.de> wrote:

> On Fri, Nov 24, 2017 at 06:23:41PM +0100, Ingo Molnar wrote:
> > From: Andy Lutomirski <luto@kernel.org>
> >
> > Historically, IDT entries from usermode have always gone directly
> > to the running task's kernel stack. Rearrange it so that we enter on
> > a percpu trampoline stack and then manually switch to the task's stack.
> > This touches a couple of extra cachelines, but it gives us a chance
> > to run some code before we touch the kernel stack.
> >
> > The asm isn't exactly beautiful, but I think that fully refactoring
> > it can wait.
> >
> > Signed-off-by: Andy Lutomirski <luto@kernel.org>
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>
> I think you mean Reviewed-by: here. The following patches have it too.
>
> > Cc: Borislav Petkov <bpetkov@suse.de>
> > Cc: Brian Gerst <brgerst@gmail.com>
> > Cc: Dave Hansen <dave.hansen@intel.com>
> > Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Link: https://lkml.kernel.org/r/fa3958723a1a85baeaf309c735b775841205800e.1511497875.git.luto@kernel.org
> > Signed-off-by: Ingo Molnar <mingo@kernel.org>
> > ---
> > arch/x86/entry/entry_64.S | 67 ++++++++++++++++++++++++++++++----------
> > arch/x86/entry/entry_64_compat.S | 5 ++-
> > arch/x86/include/asm/switch_to.h | 2 +-
> > arch/x86/include/asm/traps.h | 1 -
> > arch/x86/kernel/cpu/common.c | 6 ++--
> > arch/x86/kernel/traps.c | 18 +++++------
> > 6 files changed, 68 insertions(+), 31 deletions(-)
>
> ...
>
> > diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
> > index 8c6bd6863db9..a6796ac8d311 100644
> > --- a/arch/x86/include/asm/switch_to.h
> > +++ b/arch/x86/include/asm/switch_to.h
> > @@ -93,7 +93,7 @@ static inline void update_sp0(struct task_struct *task)
> > #ifdef CONFIG_X86_32
> > load_sp0(task->thread.sp0);
> > #else
> > - load_sp0(task_top_of_stack(task));
> > + /* On x86_64, sp0 always points to the entry trampoline stack. */
> > #endif
>
> You can put this comment to the one ontop and remove the #else.
> ifdeffery is always ugly and the less, the better.

Ok, I made it:

/* On x86_64, sp0 always points to the entry trampoline stack, which is constant: */
#ifdef CONFIG_X86_32
load_sp0(task->thread.sp0);
#endif

> > /*
> > * This is called from entry_64.S early in handling a fault
> > * caused by a bad iret to user mode. To handle the fault
> > - * correctly, we want move our stack frame to task_pt_regs
> > - * and we want to pretend that the exception came from the
> > - * iret target.
> > + * correctly, we want move our stack frame to where it would
>
> " ... we want to move... "
>
> > + * be had we entered directly on the entry stack (rather than
> > + * just below the IRET frame) and we want to pretend that the
> > + * exception came from the iret target.
>
> s/iret/IRET/
>
> > */
> > struct bad_iret_stack *new_stack =
> > - container_of(task_pt_regs(current),
> > - struct bad_iret_stack, regs);
> > + (struct bad_iret_stack *)this_cpu_read(cpu_tss.x86_tss.sp0) - 1;
> >
> > /* Copy the IRET target to the new stack. */
> > memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
> > --
>
> with that:
>
> Reviewed-by: Borislav Petkov <bp@suse.de>

Fixed those details and added your tag, thanks Boris!

Ingo

\
 
 \ /
  Last update: 2017-11-26 15:17    [W:0.105 / U:1.144 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site