linux-kernel - Re: [PATCH RESEND v8 16/16] bpf: remove CONFIG_BPF_JIT dependency on CONFIG

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Message-ID: <20240517154632.GA320@willie-the-truck>
Date: Fri, 17 May 2024 16:46:32 +0100
From: Will Deacon <will@...nel.org>
To: Klara Modin <klarasmodin@...il.com>
Cc: Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Björn Töpel <bjorn@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	"David S. Miller" <davem@...emloft.net>,
	Dinh Nguyen <dinguyen@...nel.org>,
	Donald Dutile <ddutile@...hat.com>,
	Eric Chanudet <echanude@...hat.com>,
	Heiko Carstens <hca@...ux.ibm.com>, Helge Deller <deller@....de>,
	Huacai Chen <chenhuacai@...nel.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Liviu Dudau <liviu@...au.co.uk>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nadav Amit <nadav.amit@...il.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Philippe Mathieu-Daudé <philmd@...aro.org>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Russell King <linux@...linux.org.uk>,
	Sam Ravnborg <sam@...nborg.org>, Song Liu <song@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Thomas Gleixner <tglx@...utronix.de>, bpf@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mips@...r.kernel.org, linux-mm@...ck.org,
	linux-modules@...r.kernel.org, linux-parisc@...r.kernel.org,
	linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	loongarch@...ts.linux.dev, netdev@...r.kernel.org,
	sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH RESEND v8 16/16] bpf: remove CONFIG_BPF_JIT dependency on
 CONFIG_MODULES of

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@...nel.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@...nel.org>
> > Signed-off-by: Mike Rapoport (IBM) <rppt@...nel.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;