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    SubjectRe: [tip: x86/entry] x86/entry: Convert Divide Error to IDTENTRY
    On Sun, Oct 11, 2020 at 05:25:22PM +0200, Dmitry Vyukov wrote:
    > On Tue, May 19, 2020 at 9:59 PM tip-bot2 for Thomas Gleixner
    > <tip-bot2@linutronix.de> wrote:
    > >
    > > The following commit has been merged into the x86/entry branch of tip:
    > >
    > > -DO_ERROR(X86_TRAP_DE, SIGFPE, FPE_INTDIV, IP, "divide error", divide_error)
    > >
    > > +DEFINE_IDTENTRY(exc_divide_error)
    > > +{
    > > + do_error_trap(regs, 0, "divide_error", X86_TRAP_DE, SIGFPE,
    > > + FPE_INTDIV, error_get_trap_addr(regs));
    > > +}
    >
    > I suppose this is a copy-paste typo and was supposed to be "divide
    > error", right?
    > Otherwise it changes how kernel oopses look like and breaks syzkaller
    > crash parsing, and probably of every other kernel testing system that
    > looks for kernel crashes.
    >
    > syzkaller now says just the following for divide errors, without
    > attribution to function/file/maintainers:
    >
    > kernel panic: Fatal exception (3)
    > FS: 0000000000000000(0000) GS:ffff8880ae500000(0000) knlGS:0000000000000000
    > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    > CR2: 00000000004c9428 CR3: 0000000009e8d000 CR4: 00000000001506e0
    > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    > Kernel panic - not syncing: Fatal exception in interrupt
    > Kernel Offset: disabled
    > Rebooting in 86400 seconds..
    >
    > I will fix it up in syzkaller. It is now required anyway since this
    > new crash mode is in git history, so needed for bisection and testing
    > of older releases.
    >
    > It is not the first time kernel crash output changes
    > intentionally/unintentionally breaking kernel testing.
    > But I wonder if LKDTM can be turned into actual executable tests that
    > produce pass/fail and fix crash output for different oopses?
    > Marco, you implemented some "output tests" for KCSAN. Can that be
    > extended to other crash types? With some KUnit help? However, I am not
    > sure about hard panics, they may not play well with unit-testing...

    A lot of the behavioral tests in LKDTM end up triggering arch-specific
    logging. I decided to avoid trying to consolidate it in favor of
    actually getting the test coverage. :)

    --
    Kees Cook

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