Re: CONFIG_KASAN triggers ASAN bug in GCC 13.3.0 and 14.1.0

[Ingo Molnar <mingo@kernel.org>]

* Uros Bizjak <ubizjak@gmail.com> wrote:

> On Mon, Dec 16, 2024 at 5:20 PM Matt Fleming <matt@readmodwrite.com> wrote:
> >
> > On Sat, Dec 14, 2024 at 1:17 AM Uros Bizjak <ubizjak@gmail.com> wrote:
> > >
> > > Does your config include CONFIG_UBSAN_BOOL=y ?
> >
> > Yes, it does!
> >
> > > There is a rare interaction between CONFIG_KASAN and CONFIG_UBSAN_BOOL
> > > (aka -fsanitize=bool), reported in [1] and fixed for gcc-14.2 in [2].
> > >
> > > [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111736#c42
> > >
> > > [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115172
> > >
> > > Otherwise, please attach your .config, and I'll look into this issue.
> >
> > Thanks. Disabling CONFIG_UBSAN_BOOL does indeed make the kernels boot again.
> >
> > Should CONFIG_UBSAN_BOOL have a dependency on GCC 14.4+ ?
> 
> No, this is a very rare Oops that triggers only with gcc-14.1 version
> and only when both KASAN and UBSAN are enabled. This is actually the
> problem with sanitization of the percpu address when named address
> spaces are enabled (IOW, sanitization of __seg_gs prefixed address).
> UBSAN creates a temporary in memory, but forgets to copy memory tags,
> including named address space qualifier from the original. Later ASAN
> sanitizes this location as a normal variable (due to missing
> qualifier), but actually should be disabled for __seg_gs prefixed
> addresses.
> 
> Your report is only *the second* since sanitizers were re-enabled with
> named address spaces. gcc-14.2 that includes the fix is available
> since August 2024, and since sanitizers are strictly development
> tools, my proposed solution would be to simply upgrade the compiler to
> gcc-14.2 release.

So unless this is difficult to test for, it would be nice to have a 
compiler version cutoff for the feature. Especially if it's been 
reported twice already, chances are that a lot more people have 
experienced it already.

The kernel build should avoid this known oops automatically.

Thanks,

	Ingo