From: Sohil Mehta <sohil.mehta@intel.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
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"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Ard Biesheuvel <ardb@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Xiongwei Song <xiongwei.song@windriver.com>,
Xin Li <xin3.li@intel.com>,
"Mike Rapoport (IBM)" <rppt@kernel.org>,
Brijesh Singh <brijesh.singh@amd.com>,
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Tony Luck <tony.luck@intel.com>,
Alexey Kardashevskiy <aik@amd.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@kernel.org>,
"Pawan Gupta" <pawan.kumar.gupta@linux.intel.com>,
Daniel Sneddon <daniel.sneddon@linux.intel.com>,
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"Masami Hiramatsu (Google)" <mhiramat@kernel.org>,
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"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
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Tejun Heo <tj@kernel.org>, Changbin Du <changbin.du@huawei.com>,
Huang Shijie <shijie@os.amperecomputing.com>,
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Namhyung Kim <namhyung@kernel.org>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
<linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<linux-efi@vger.kernel.org>, <linux-mm@kvack.org>
Subject: Re: [PATCHv8 03/17] x86/alternatives: Disable LASS when patching kernel alternatives
Date: Tue, 1 Jul 2025 11:44:04 -0700 [thread overview]
Message-ID: <fd8c912c-89d4-4933-a3f8-f0a38a3c3482@intel.com> (raw)
In-Reply-To: <20250701095849.2360685-4-kirill.shutemov@linux.intel.com>
On 7/1/2025 2:58 AM, Kirill A. Shutemov wrote:
>
> +/*
> + * The CLAC/STAC instructions toggle the enforcement of X86_FEATURE_SMAP and
> + * X86_FEATURE_LASS.
> + *
> + * SMAP enforcement is based on the _PAGE_BIT_USER bit in the page tables: the
> + * kernel is not allowed to touch pages with the bit set unless the AC bit is
> + * set.
> + *
> + * LASS enforcement is based on bit 63 of the virtual address. The kernel is
> + * not allowed to touch memory in the lower half of the virtual address space
> + * unless the AC bit is set.
> + *
> + * Use stac()/clac() when accessing userspace (_PAGE_USER) mappings,
> + * regardless of location.
> + *
> + * Use lass_stac()/lass_clac() when accessing kernel mappings (!_PAGE_USER)
> + * in the lower half of the address space.
> + *
> + * Note: a barrier is implicit in alternative().
> + */
> +
Thank you for incorporating my feedback. I like the updated wording.
next parent reply other threads:[~2025-07-01 18:44 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20250701095849.2360685-1-kirill.shutemov@linux.intel.com>
[not found] ` <20250701095849.2360685-4-kirill.shutemov@linux.intel.com>
2025-07-01 18:44 ` Sohil Mehta [this message]
[not found] ` <20250701095849.2360685-12-kirill.shutemov@linux.intel.com>
2025-07-01 22:51 ` [PATCHv8 11/17] x86/cpu: Set LASS CR4 bit as pinning sensitive Sohil Mehta
[not found] ` <20250701095849.2360685-16-kirill.shutemov@linux.intel.com>
2025-07-01 23:03 ` [PATCHv8 15/17] x86/cpu: Make LAM depend on LASS Sohil Mehta
[not found] ` <20250701095849.2360685-5-kirill.shutemov@linux.intel.com>
2025-07-01 19:03 ` [PATCHv8 04/17] x86/cpu: Defer CR pinning setup until after EFI initialization Sohil Mehta
2025-07-02 9:47 ` Kirill A. Shutemov
2025-07-01 23:10 ` Dave Hansen
2025-07-02 10:05 ` Kirill A. Shutemov
2025-07-04 12:23 ` Kirill A. Shutemov
[not found] ` <20250701095849.2360685-18-kirill.shutemov@linux.intel.com>
2025-07-01 23:13 ` [PATCHv8 17/17] x86: Re-enable Linear Address Masking Sohil Mehta
[not found] ` <20250701095849.2360685-13-kirill.shutemov@linux.intel.com>
2025-07-02 0:36 ` [PATCHv8 12/17] x86/traps: Communicate a LASS violation in #GP message Sohil Mehta
2025-07-02 10:10 ` Kirill A. Shutemov
[not found] ` <20250701095849.2360685-14-kirill.shutemov@linux.intel.com>
2025-07-02 0:54 ` [PATCHv8 13/17] x86/traps: Generalize #GP address decode and hint code Sohil Mehta
[not found] ` <20250701095849.2360685-15-kirill.shutemov@linux.intel.com>
2025-07-02 1:35 ` [PATCHv8 14/17] x86/traps: Handle LASS thrown #SS Sohil Mehta
2025-07-02 2:00 ` H. Peter Anvin
2025-07-02 2:06 ` H. Peter Anvin
2025-07-02 10:17 ` Kirill A. Shutemov
2025-07-02 14:37 ` H. Peter Anvin
2025-07-02 14:47 ` Kirill A. Shutemov
2025-07-02 17:10 ` H. Peter Anvin
2025-07-02 23:42 ` Andrew Cooper
2025-07-03 0:44 ` H. Peter Anvin
2025-07-06 9:22 ` David Laight
2025-07-06 15:07 ` H. Peter Anvin
2025-07-02 13:27 ` Kirill A. Shutemov
2025-07-02 17:56 ` Sohil Mehta
2025-07-03 10:40 ` Kirill A. Shutemov
2025-07-02 20:05 ` Sohil Mehta
2025-07-03 11:31 ` Kirill A. Shutemov
2025-07-03 20:12 ` Sohil Mehta
2025-07-04 9:23 ` Kirill A. Shutemov
[not found] ` <20250701095849.2360685-3-kirill.shutemov@linux.intel.com>
2025-07-03 8:44 ` [PATCHv8 02/17] x86/asm: Introduce inline memcpy and memset David Laight
2025-07-03 10:39 ` Kirill A. Shutemov
2025-07-03 12:15 ` David Laight
2025-07-03 13:33 ` Vegard Nossum
2025-07-03 16:52 ` David Laight
2025-07-03 14:10 ` Kirill A. Shutemov
2025-07-03 17:02 ` David Laight
2025-07-03 17:13 ` Dave Hansen
2025-07-04 9:04 ` Kirill A. Shutemov
2025-07-06 9:13 ` David Laight
2025-07-07 8:02 ` Kirill A. Shutemov
2025-07-07 9:33 ` David Laight
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