From: "H. Peter Anvin" <hpa@zytor.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Xiang Mei <xmei5@asu.edu>, Pedro Falcato <pfalcato@suse.de>,
Kees Cook <kees@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, linux-hardening@vger.kernel.org,
Uladzislau Rezki <urezki@gmail.com>,
"Gustavo A . R . Silva" <gustavoars@kernel.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Jennifer Miller <jmill@asu.edu>, Tiffany Bao <tbao@asu.edu>,
Ruoyu Wang <fishw@asu.edu>, Adam Doupe <doupe@asu.edu>,
Kyle Zeng <zengyhkyle@asu.edu>,
Yan Shoshitaishvili <yans@asu.edu>
Subject: Re: [PATCH] mm/vmalloc: widen guard region to defeat ENTER-based stack pivot
Date: Mon, 29 Jun 2026 05:50:08 -0700 [thread overview]
Message-ID: <3c4094d8-ae5e-4ffd-b28a-0c10db50296c@zytor.com> (raw)
In-Reply-To: <akH34ycu5-q2Yc_D@casper.infradead.org>
On 2026-06-28 21:43, Matthew Wilcox wrote:
> On Sun, Jun 28, 2026 at 07:09:37PM -0700, H. Peter Anvin wrote:
>>
>>> 2) `enter` is not rare since we can take part in the instruction.
>>
>> This sentence doesn't parse.
>
> They mean that we can jump into the middle of an instruction, and it is
> not rare to see a 'c8' byte in the instruction stream.
>
OK, I see the point now. The main difference is that ENTER doesn't require a
REX prefix, whereas ADD/SUB/LEA do (otherwise it truncates RSP and everything
immediately dies as a result of SMAP violations [you are welcome].)
This means that an offending bit combination is far less common.
-hpa
next prev parent reply other threads:[~2026-06-29 12:51 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-26 17:34 Xiang Mei
2026-06-26 17:46 ` Xiang Mei
2026-06-26 17:48 ` Xiang Mei
2026-06-30 7:12 ` Peter Zijlstra
2026-06-30 8:09 ` Xiang Mei
2026-06-26 19:39 ` Pedro Falcato
2026-06-26 20:05 ` Xiang Mei
2026-06-29 2:09 ` H. Peter Anvin
2026-06-29 4:43 ` Matthew Wilcox
2026-06-29 12:50 ` H. Peter Anvin [this message]
2026-06-29 17:21 ` Xiang Mei
2026-06-29 21:50 ` Xiang Mei
2026-06-29 21:51 ` Xiang Mei
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