Re: [PATCH RESEND v8 16/16] bpf: remove CONFIG_BPF_JIT dependency on CONFIG_MODULES of

Will Deacon
2024-05-17T15:46:44Z

Hi Klara,

On Fri, May 17, 2024 at 01:00:31AM +0200, Klara Modin wrote:
> On 2024-05-05 18:06, Mike Rapoport wrote:
> > From: "Mike Rapoport (IBM)" <rppt@kernel.org>
> >
> > BPF just-in-time compiler depended on CONFIG_MODULES because it used
> > module_alloc() to allocate memory for the generated code.
> >
> > Since code allocations are now implemented with execmem, drop dependency of
> > CONFIG_BPF_JIT on CONFIG_MODULES and make it select CONFIG_EXECMEM.
> >
> > Suggested-by: Björn Töpel <bjorn@kernel.org>
> > Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
> > ---
> > kernel/bpf/Kconfig | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
> > index bc25f5098a25..f999e4e0b344 100644
> > --- a/kernel/bpf/Kconfig
> > +++ b/kernel/bpf/Kconfig
> > @@ -43,7 +43,7 @@ config BPF_JIT
> > bool "Enable BPF Just In Time compiler"
> > depends on BPF
> > depends on HAVE_CBPF_JIT || HAVE_EBPF_JIT
> > - depends on MODULES
> > + select EXECMEM
> > help
> > BPF programs are normally handled by a BPF interpreter. This option
> > allows the kernel to generate native code when a program is loaded
>
> This does not seem to work entirely. If build with BPF_JIT without module
> support for my Raspberry Pi 3 B I get warnings in my kernel log (easiest way
> to trigger it seems to be trying to ssh into it, which fails).

Thanks for the report. I was able to reproduce this using QEMU and it
looks like the problem is because bpf_arch_text_copy() silently fails
to write to the read-only area as a result of patch_map() faulting and
the resulting -EFAULT being chucked away.

Please can you try the diff below?

Will

--->8

diff --git a/arch/arm64/kernel/patching.c b/arch/arm64/kernel/patching.c
index 255534930368..94b9fea65aca 100644
--- a/arch/arm64/kernel/patching.c
+++ b/arch/arm64/kernel/patching.c
@@ -36,7 +36,7 @@ static void __kprobes *patch_map(void *addr, int fixmap)

if (image)
page = phys_to_page(__pa_symbol(addr));
- else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
+ else if (IS_ENABLED(CONFIG_EXECMEM))
page = vmalloc_to_page(addr);
else
return addr;