lkml.org 
[lkml]   [2020]   [May]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[patch V4 part 1 08/36] x86/doublefault: Remove memmove() call
    Use of memmove() in #DF is problematic considered tracing and other
    instrumentation.

    Remove the memmove() call and simply write out what needs doing; this
    even clarifies the code, win-win! The code copies from the espfix64
    stack to the normal task stack, there is no possible way for that to
    overlap.

    Survives selftests/x86, specifically sigreturn_64.

    Suggested-by: Borislav Petkov <bp@alien8.de>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Andy Lutomirski <luto@kernel.org>
    Link: https://lkml.kernel.org/r/20200220121727.GB507@zn.tnic
    ---
    arch/x86/kernel/traps.c | 7 ++++++-
    1 file changed, 6 insertions(+), 1 deletion(-)

    --- a/arch/x86/kernel/traps.c
    +++ b/arch/x86/kernel/traps.c
    @@ -278,6 +278,7 @@ dotraplinkage void do_double_fault(struc
    regs->ip == (unsigned long)native_irq_return_iret)
    {
    struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
    + unsigned long *p = (unsigned long *)regs->sp;

    /*
    * regs->sp points to the failing IRET frame on the
    @@ -285,7 +286,11 @@ dotraplinkage void do_double_fault(struc
    * in gpregs->ss through gpregs->ip.
    *
    */
    - memmove(&gpregs->ip, (void *)regs->sp, 5*8);
    + gpregs->ip = p[0];
    + gpregs->cs = p[1];
    + gpregs->flags = p[2];
    + gpregs->sp = p[3];
    + gpregs->ss = p[4];
    gpregs->orig_ax = 0; /* Missing (lost) #GP error code */

    /*
    \
     
     \ /
      Last update: 2020-05-05 16:24    [W:3.460 / U:0.088 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site