linux-kernel - Re: [PATCH bpf-next v10 3/3] arm64/cfi,bpf: Support kCFI + BPF on arm64

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Message-ID: <aHozPj7NIudHmmgM@willie-the-truck>
Date: Fri, 18 Jul 2025 12:42:54 +0100
From: Will Deacon <will@...nel.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: bpf@...r.kernel.org, Puranjay Mohan <puranjay@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Catalin Marinas <catalin.marinas@....com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Maxwell Bland <mbland@...orola.com>,
	Puranjay Mohan <puranjay12@...il.com>,
	Dao Huang <huangdao1@...o.com>
Subject: Re: [PATCH bpf-next v10 3/3] arm64/cfi,bpf: Support kCFI + BPF on
 arm64

On Tue, Jul 15, 2025 at 10:57:37PM +0000, Sami Tolvanen wrote:
> From: Puranjay Mohan <puranjay12@...il.com>
> 
> Currently, bpf_dispatcher_*_func() is marked with `__nocfi` therefore
> calling BPF programs from this interface doesn't cause CFI warnings.
> 
> When BPF programs are called directly from C: from BPF helpers or
> struct_ops, CFI warnings are generated.
> 
> Implement proper CFI prologues for the BPF programs and callbacks and
> drop __nocfi for arm64. Fix the trampoline generation code to emit kCFI
> prologue when a struct_ops trampoline is being prepared.
> 
> Signed-off-by: Puranjay Mohan <puranjay12@...il.com>
> Co-developed-by: Maxwell Bland <mbland@...orola.com>
> Signed-off-by: Maxwell Bland <mbland@...orola.com>
> Co-developed-by: Sami Tolvanen <samitolvanen@...gle.com>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Tested-by: Dao Huang <huangdao1@...o.com>
> ---
>  arch/arm64/include/asm/cfi.h  |  7 +++++++
>  arch/arm64/net/bpf_jit_comp.c | 22 +++++++++++++++++++---
>  2 files changed, 26 insertions(+), 3 deletions(-)
>  create mode 100644 arch/arm64/include/asm/cfi.h

> diff --git a/arch/arm64/include/asm/cfi.h b/arch/arm64/include/asm/cfi.h
> new file mode 100644
> index 000000000000..ab90f0351b7a
> --- /dev/null
> +++ b/arch/arm64/include/asm/cfi.h
> @@ -0,0 +1,7 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_ARM64_CFI_H
> +#define _ASM_ARM64_CFI_H
> +
> +#define __bpfcall
> +
> +#endif /* _ASM_ARM64_CFI_H */

So close to not needing the arch header at all!

Acked-by: Will Deacon <will@...nel.org>

Will