lkml.org 
[lkml]   [2008]   [Apr]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH 1/1] x86: fix text_poke

    * Linus Torvalds <torvalds@linux-foundation.org> wrote:

    > > Not sure how the fixmap is better. It's pretty much equivalent,
    > > isn't it? Perhaps a little cheaper, but the code shouldn't be
    > > performance critical.
    >
    > I have no really strong opinions. However, we do have a *lot* of lock
    > prefixes in the kernel, and fixmaps are a lot cheaper than vmap(). It
    > may not be performance-critical, but for me the "locks" section for
    > the kernel is 0x8060 bytes long, which would seem to say that this is
    > called four thousand times for each suspend and resume.
    >
    > With each invocation being thousands of instructions and a cross-CPU
    > IPI for the tlb flush, that kind of stuff adds up. We're likely
    > talking real fractions of a second, rather than milliseconds.

    the other thing is atomicity - your new version of text_poke() is
    evidently atomic - while vmap() does a kmalloc which might sleep.
    Atomicity for something as fragile as code-patching never hurts, so i
    definitely like your version more.

    it's also the more familar API - set_fixmap() is used more frequently
    than vmap() - hence less danger of doing something wrong.

    in fact i'd do the extra sanity check below as well on top of your patch
    - all core kernel text pages are PageReserved so the one below would
    have caught the memory corruption right at its source.

    Ingo

    ---------------->
    Subject: x86: harden kernel code patching
    From: Ingo Molnar <mingo@elte.hu>
    Date: Fri Apr 25 17:07:03 CEST 2008

    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    arch/x86/kernel/alternative.c | 2 ++
    1 file changed, 2 insertions(+)

    Index: linux/arch/x86/kernel/alternative.c
    ===================================================================
    --- linux.orig/arch/x86/kernel/alternative.c
    +++ linux/arch/x86/kernel/alternative.c
    @@ -522,6 +522,8 @@ void *__kprobes text_poke(void *addr, co
    unsigned long virt = fix_to_virt(FIX_POKE);
    phys &= PAGE_MASK;

    + WARN_ON(!PageReserved(virt_to_page(addr)));
    +
    spin_lock_irqsave(&poke_lock, flags);
    set_fixmap(FIX_POKE, phys);
    memcpy((void *)(virt + offset), opcode, len);

    \
     
     \ /
      Last update: 2008-04-25 18:37    [W:3.257 / U:0.216 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site