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Date: Thu, 4 Jun 2026 16:40:31 -0600 (MDT)
From: Paul Walmsley <pjw@kernel.org>
To: Richard Patel <ripatel@wii.dev>
cc: Paul Walmsley <pjw@kernel.org>, Palmer Dabbelt <palmer@dabbelt.com>, 
    Albert Ou <aou@eecs.berkeley.edu>, Alexandre Ghiti <alex@ghiti.fr>, 
    Deepak Gupta <debug@rivosinc.com>, Zong Li <zong.li@sifive.com>, 
    Charlie Jenkins <charlie@rivosinc.com>, Shuah Khan <shuah@kernel.org>, 
    linux-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org, 
    linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: cfi: reject unknown flags in PR_SET_CFI
In-Reply-To: <20260518183918.322545-1-ripatel@wii.dev>
Message-ID: <3f2d4628-a95d-89c3-2fd7-3e1a407d698a@kernel.org>
References: <20260518183918.322545-1-ripatel@wii.dev>
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Hi,

On Mon, 18 May 2026, Richard Patel wrote:

> prctl(PR_SET_CFI,PR_CFI_BRANCH_LANDING_PADS) silently ignored
> unknown control values. Only PR_CFI_{ENABLE,DISABLE,LOCK} should
> be permitted.
<
> This is a uABI breaking change (fails previously accepted bits
> with EINVAL).

Thanks for the patch.  However, I'm not convinced that this actually 
breaks anything.  The behavior of the interface changes when unknown flags 
are specified, but I'm not aware of anything that relies on this specific 
behavior.

Does that match your understanding?


- Paul