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[209.85.221.47]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-afded479020sm615071066b.74.2025.08.22.06.52.09 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 22 Aug 2025 06:52:09 -0700 (PDT) Received: by mail-wr1-f47.google.com with SMTP id ffacd0b85a97d-3c6df24f128so64883f8f.3 for ; Fri, 22 Aug 2025 06:52:09 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCUMZjzZ9aZ4ZsKJ6KsPHgK3o5IT68Nra5WrTrlteNbGWZ5V16yYwzbKDNSZTVr+yrUGkfy0YRljlw==@kvack.org X-Received: by 2002:a05:6402:5110:b0:615:6481:d1c with SMTP id 4fb4d7f45d1cf-61c1b450840mr2274281a12.1.1755870414406; Fri, 22 Aug 2025 06:46:54 -0700 (PDT) MIME-Version: 1.0 References: <82b9c88e63a6f1f5926e39471364168b345d84cc.1755854833.git.christophe.leroy@csgroup.eu> In-Reply-To: <82b9c88e63a6f1f5926e39471364168b345d84cc.1755854833.git.christophe.leroy@csgroup.eu> From: Linus Torvalds Date: Fri, 22 Aug 2025 09:46:37 -0400 X-Gmail-Original-Message-ID: X-Gm-Features: Ac12FXyg7aT4BFeJsiyaeWdfrE2FPhwu5xUJIJ1D8_vj4L1z_hVeZFuzgKfsNNk Message-ID: Subject: Re: [PATCH v2 02/10] uaccess: Add speculation barrier to copy_from_user_iter() To: Christophe Leroy Cc: Michael Ellerman , Nicholas Piggin , Madhavan Srinivasan , Alexander Viro , Christian Brauner , Jan Kara , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Darren Hart , Davidlohr Bueso , Andre Almeida , Andrew Morton , David Laight , Dave Hansen , Daniel Borkmann , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: DE050160011 X-Stat-Signature: ea6ajcob8wu9gqunqx38hywb1stphm5y X-HE-Tag: 1755870731-78391 X-HE-Meta: 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 5359a1zg 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 22 Aug 2025 at 05:58, Christophe Leroy wrote: > > The results of "access_ok()" can be mis-speculated. The result is that > you can end speculatively: > > if (access_ok(from, size)) > // Right here I actually think that we should probably just make access_ok() itself do this. We don't have *that* many users since we have been de-emphasizing the "check ahead of time" model, and any that are performance-critical can these days be turned into masked addresses. As it is, now we're in the situation that careful places - like _inline_copy_from_user(), and with your patch copy_from_user_iter() - do maybe wethis by hand and are ugly as a result, and lazy and probably incorrect places don't do it at all. That said, I don't object to this patch and maybe we should do that access_ok() change later and independently of any powerpc work. Linus