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SubjectRe: Sysenter crash with Nested Task Bit set
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On Sun, 2006-09-17 at 22:25 -0700, Andrew Morton wrote:
> On Sun, 17 Sep 2006 23:51:45 -0400
> Chuck Ebbert <76306.1226@compuserve.com> wrote:
>
> > In-Reply-To: <5a20704e0609171608o7ee45fdbxb94aa897c1776153@mail.gmail.com>
> >
> > On Sun, 17 Sep 2006 19:08:24 -0400, "In Cognito" wrote:
> >
> > > Here's a way to heat up your cpu and crash the rest of the system too:
> > >
> > > main(){
> > > asm("pushf\n"
> > > "popl %eax\n"
> > > /* enable the NT bit */
> > > "orl $0x4000, %eax\n"
> > > "pushl %eax\n"
> > > "popf\n"
> > >
> > > "sysenter\n"
> > > );
> > > return 0;
> > > }
> >
> > I'll take your word that it crashes.
>
> It doesn't for me - I get a segfault.
>
> That's on a PIII. Are recenter CPUs different in this regard?

I guess so. That proglet does very bad things to my P4/HT. I too get a
segfault, but then init goes insane and may reap the proglet's parent
shell, but then again, it may decide to reap the shell next door.
Thereafter, init is running/gaga. (18-rc7)

Chuck's patch did indeed make it stop doing that.

> > 2.6.9 is fine. I'd guess the iret fixups from 2.6.12 are the problem.
> >
> > This doesn't crash for me, but it's probably not quite the right fix:
> >
> > Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
> > ---
> > arch/i386/kernel/traps.c | 12 +++++++++++-
> > 1 files changed, 11 insertions(+), 1 deletion(-)
> >
> > --- 2.6.18-rc6-nb.orig/arch/i386/kernel/traps.c
> > +++ 2.6.18-rc6-nb/arch/i386/kernel/traps.c
> > @@ -516,6 +516,16 @@ fastcall void do_##name(struct pt_regs *
> > do_trap(trapnr, signr, str, 0, regs, error_code, NULL); \
> > }
> >
> > +#define DO_TSS_ERROR(trapnr, signr, str, name) \
> > +fastcall void do_##name(struct pt_regs * regs, long error_code) \
> > +{ \
> > + if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) \
> > + == NOTIFY_STOP) \
> > + return; \
> > + regs->eflags &= ~X86_EFLAGS_NT; \
> > + do_trap(trapnr, signr, str, 0, regs, error_code, NULL); \
> > +}
> > +
> > #define DO_ERROR_INFO(trapnr, signr, str, name, sicode, siaddr) \
> > fastcall void do_##name(struct pt_regs * regs, long error_code) \
> > { \
> > @@ -561,7 +571,7 @@ DO_VM86_ERROR( 4, SIGSEGV, "overflow", o
> > DO_VM86_ERROR( 5, SIGSEGV, "bounds", bounds)
> > DO_ERROR_INFO( 6, SIGILL, "invalid opcode", invalid_op, ILL_ILLOPN, regs->eip)
> > DO_ERROR( 9, SIGFPE, "coprocessor segment overrun", coprocessor_segment_overrun)
> > -DO_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
> > +DO_TSS_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
> > DO_ERROR(11, SIGBUS, "segment not present", segment_not_present)
> > DO_ERROR(12, SIGBUS, "stack segment", stack_segment)
> > DO_ERROR_INFO(17, SIGBUS, "alignment check", alignment_check, BUS_ADRALN, 0)
> > --
> > Chuck
> -
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