From: Dave Hansen <dave.hansen@intel.com>
To: Sohil Mehta <sohil.mehta@intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, Andy Lutomirski <luto@kernel.org>,
Borislav Petkov <bp@alien8.de>
Cc: Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Kiryl Shutsemau <kas@kernel.org>,
Brendan Jackman <jackmanb@google.com>,
Sean Christopherson <seanjc@google.com>,
Nam Cao <namcao@linutronix.de>,
Cedric Xing <cedric.xing@intel.com>,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Tony Luck <tony.luck@intel.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Maciej Wieczor-Retman <m.wieczorretman@pm.me>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/5] x86/vsyscall: Disable LASS if vsyscall mode is set to EMULATE
Date: Tue, 3 Mar 2026 08:33:31 -0800 [thread overview]
Message-ID: <c6385777-b99b-48ba-a2cf-888f58de6bb6@intel.com> (raw)
In-Reply-To: <20260219233600.154313-5-sohil.mehta@intel.com>
On 2/19/26 15:35, Sohil Mehta wrote:
> The EMULATE mode of vsyscall maps the vsyscall page with a high kernel
> address directly into user address space. Reading the vsyscall page in
> EMULATE mode would cause LASS to trigger a #GP.
>
> Fixing the LASS violation in EMULATE mode would require complex
> instruction decoding because the resulting #GP does not include any
> useful error information, and the vsyscall address is not readily
> available in the RIP.
>
> The EMULATE mode has been deprecated since 2022 and can only be enabled
> using the command line parameter vsyscall=emulate. See commit
> bf00745e7791 ("x86/vsyscall: Remove CONFIG_LEGACY_VSYSCALL_EMULATE") for
> details. At this point, no one is expected to be using this insecure
> mode. The rare usages that need it obviously do not care about security.
>
> Disable LASS when EMULATE mode is requested to avoid breaking legacy
> user software. Also, update the vsyscall documentation to reflect this.
> LASS will only be supported if vsyscall mode is set to XONLY (default)
> or NONE.
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
next prev parent reply other threads:[~2026-03-03 16:33 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-19 23:35 [PATCH 0/5] x86: Enable LASS support with vsyscall emulation Sohil Mehta
2026-02-19 23:35 ` [PATCH 1/5] x86/vsyscall: Reorganize the page fault emulation code Sohil Mehta
2026-02-19 23:35 ` [PATCH 2/5] x86/traps: Consolidate user fixups in the #GP handler Sohil Mehta
2026-02-19 23:35 ` [PATCH 3/5] x86/vsyscall: Add vsyscall emulation for #GP Sohil Mehta
2026-03-03 15:51 ` Dave Hansen
2026-03-03 21:20 ` Sohil Mehta
2026-03-03 22:35 ` H. Peter Anvin
2026-03-05 0:10 ` Sohil Mehta
2026-03-05 1:45 ` Dave Hansen
2026-03-05 6:31 ` H. Peter Anvin
2026-03-05 7:56 ` Sohil Mehta
2026-03-05 6:32 ` H. Peter Anvin
2026-02-19 23:35 ` [PATCH 4/5] x86/vsyscall: Disable LASS if vsyscall mode is set to EMULATE Sohil Mehta
2026-03-03 16:33 ` Dave Hansen [this message]
2026-02-19 23:36 ` [PATCH 5/5] x86/cpu: Remove LASS restriction on vsyscall emulation Sohil Mehta
2026-03-03 16:37 ` Dave Hansen
2026-03-03 16:27 ` [PATCH 0/5] x86: Enable LASS support with " Dave Hansen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=c6385777-b99b-48ba-a2cf-888f58de6bb6@intel.com \
--to=dave.hansen@intel.com \
--cc=alexander.shishkin@linux.intel.com \
--cc=andrew.cooper3@citrix.com \
--cc=bp@alien8.de \
--cc=cedric.xing@intel.com \
--cc=corbet@lwn.net \
--cc=dave.hansen@linux.intel.com \
--cc=hpa@zytor.com \
--cc=jackmanb@google.com \
--cc=kas@kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=m.wieczorretman@pm.me \
--cc=mingo@redhat.com \
--cc=namcao@linutronix.de \
--cc=peterz@infradead.org \
--cc=rick.p.edgecombe@intel.com \
--cc=seanjc@google.com \
--cc=skhan@linuxfoundation.org \
--cc=sohil.mehta@intel.com \
--cc=tglx@kernel.org \
--cc=tony.luck@intel.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox