From: Linus Torvalds <torvalds@linux-foundation.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
Nicholas Piggin <npiggin@gmail.com>,
Madhavan Srinivasan <maddy@linux.ibm.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Darren Hart <dvhart@infradead.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Andre Almeida <andrealmeid@igalia.com>,
Andrew Morton <akpm@linux-foundation.org>,
David Laight <david.laight.linux@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Daniel Borkmann <daniel@iogearbox.net>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
linux-block@vger.kernel.org
Subject: Re: [PATCH v2 02/10] uaccess: Add speculation barrier to copy_from_user_iter()
Date: Fri, 22 Aug 2025 09:46:37 -0400 [thread overview]
Message-ID: <CAHk-=whKeVCEtR2mQJQjT2ndSOXGDdb+L0=WoVUQUGumm88VpA@mail.gmail.com> (raw)
In-Reply-To: <82b9c88e63a6f1f5926e39471364168b345d84cc.1755854833.git.christophe.leroy@csgroup.eu>
On Fri, 22 Aug 2025 at 05:58, Christophe Leroy
<christophe.leroy@csgroup.eu> 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
next prev parent reply other threads:[~2025-08-22 13:52 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-22 9:57 [PATCH v2 00/10] powerpc: Implement masked user access Christophe Leroy
2025-08-22 9:57 ` [PATCH v2 01/10] iter: Avoid barrier_nospec() in copy_from_user_iter() Christophe Leroy
2025-08-22 9:57 ` [PATCH v2 02/10] uaccess: Add speculation barrier to copy_from_user_iter() Christophe Leroy
2025-08-22 13:46 ` Linus Torvalds [this message]
2025-08-22 14:11 ` Giorgi Tchankvetadze
2025-08-22 18:53 ` David Laight
2025-08-22 9:57 ` [PATCH v2 03/10] uaccess: Add masked_user_{read/write}_access_begin Christophe Leroy
2025-08-24 15:08 ` Thomas Gleixner
2025-08-22 9:58 ` [PATCH v2 04/10] powerpc/uaccess: Move barrier_nospec() out of allow_read_{from/write}_user() Christophe Leroy
2025-08-22 9:58 ` [PATCH v2 05/10] powerpc/uaccess: Remove unused size and from parameters from allow_access_user() Christophe Leroy
2025-08-22 9:58 ` [PATCH v2 06/10] powerpc/uaccess: Remove {allow/prevent}_{read/write/read_write}_{from/to/}_user() Christophe Leroy
2025-08-22 9:58 ` [PATCH v2 07/10] powerpc/uaccess: Refactor user_{read/write/}_access_begin() Christophe Leroy
2025-08-22 9:58 ` [PATCH v2 08/10] powerpc/32s: Fix segments setup when TASK_SIZE is not a multiple of 256M Christophe Leroy
2025-08-22 9:58 ` [PATCH v2 09/10] powerpc/32: Automatically adapt TASK_SIZE based on constraints Christophe Leroy
2025-08-22 12:04 ` David Laight
2025-08-22 9:58 ` [PATCH v2 10/10] powerpc/uaccess: Implement masked user access Christophe Leroy
2025-08-25 9:04 ` Gabriel Paubert
2025-08-25 9:40 ` Christophe Leroy
2025-08-25 10:18 ` Gabriel Paubert
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