Re: [PATCH RFC bpf-next 3/8] bpf: add BPF_JIT_KASAN for KASAN instrumentation of JITed programs

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Tue, Apr 14, 2026 at 6:24 AM Alexis Lothoré
<alexis.lothore@bootlin.com> wrote:
>
> On Tue Apr 14, 2026 at 12:20 AM CEST, Andrey Konovalov wrote:
> > On Mon, Apr 13, 2026 at 8:29 PM Alexis Lothoré (eBPF Foundation)
> > <alexis.lothore@bootlin.com> wrote:
> >>
> >> Add a new Kconfig option CONFIG_BPF_JIT_KASAN that automatically enables
> >> KASAN (Kernel Address Sanitizer) memory access checks for JIT-compiled
> >> BPF programs, when both KASAN and JIT compiler are enabled. When
> >> enabled, the JIT compiler will emit shadow memory checks before memory
> >> loads and stores to detect use-after-free, out-of-bounds, and other
> >> memory safety bugs at runtime. The option is gated behind
> >> HAVE_EBPF_JIT_KASAN, as it needs proper arch-specific implementation.
> >>
> >> Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
> >> ---
> >>  kernel/bpf/Kconfig | 9 +++++++++
> >>  1 file changed, 9 insertions(+)
> >>
> >> diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
> >> index eb3de35734f0..28392adb3d7e 100644
> >> --- a/kernel/bpf/Kconfig
> >> +++ b/kernel/bpf/Kconfig
> >> @@ -17,6 +17,10 @@ config HAVE_CBPF_JIT
> >>  config HAVE_EBPF_JIT
> >>         bool
> >>
> >> +# KASAN support for JIT compiler
> >> +config HAVE_EBPF_JIT_KASAN
> >> +       bool
> >> +
> >>  # Used by archs to tell that they want the BPF JIT compiler enabled by
> >>  # default for kernels that were compiled with BPF JIT support.
> >>  config ARCH_WANT_DEFAULT_BPF_JIT
> >> @@ -101,4 +105,9 @@ config BPF_LSM
> >>
> >>           If you are unsure how to answer this question, answer N.
> >>
> >> +config BPF_JIT_KASAN
> >> +       bool
> >> +       depends on HAVE_EBPF_JIT_KASAN
> >> +       default y if BPF_JIT && KASAN_GENERIC
> >
> > Should this be "depends on KASAN && KASAN_GENERIC"?
>
> Meaning, making it an explicit user-selectable option ?
>
> If so, the current design choice is voluntary and based on the feedback
> received on the original RFC, where I have been suggested to
> automatically enable the KASAN instrumentation in BPF programs if KASAN
> support is enabled in the kernel ([1]). But if a user-selectable toggle
> is eventually a better solution, I'm fine with changing it.

Let's not add more config knobs.
Even this patch looks redundant.
Inside JIT do instrumentation when KASAN_GENERIC is set.