linux-kernel - Re: [PATCHv16 13/17] selftests/x86/lam: Add mmap and SYSCALL test cases for linear-address masking

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <lhupld4zdjp.fsf@oldenburg.str.redhat.com>
Date: Sat, 09 Aug 2025 18:04:58 +0200
From: Florian Weimer <fweimer@...hat.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,  Andy Lutomirski
 <luto@...nel.org>,  Peter Zijlstra <peterz@...radead.org>,
  x86@...nel.org,  Kostya Serebryany <kcc@...gle.com>,  Andrey Ryabinin
 <ryabinin.a.a@...il.com>,  Andrey Konovalov <andreyknvl@...il.com>,
  Alexander Potapenko <glider@...gle.com>,  Taras Madan
 <tarasmadan@...gle.com>,  Dmitry Vyukov <dvyukov@...gle.com>,  "H . J .
 Lu" <hjl.tools@...il.com>,  Andi Kleen <ak@...ux.intel.com>,  Rick
 Edgecombe <rick.p.edgecombe@...el.com>,  Bharata B Rao <bharata@....com>,
  Jacob Pan <jacob.jun.pan@...ux.intel.com>,  Ashok Raj
 <ashok.raj@...el.com>,  Linus Torvalds <torvalds@...ux-foundation.org>,
  linux-mm@...ck.org,  linux-kernel@...r.kernel.org,  Weihong Zhang
 <weihong.zhang@...el.com>
Subject: Re: [PATCHv16 13/17] selftests/x86/lam: Add mmap and SYSCALL test
 cases for linear-address masking

* Kirill A. Shutemov:

> From: Weihong Zhang <weihong.zhang@...el.com>
>
> Add mmap and SYSCALL test cases.
>
> SYSCALL test cases:
>
>  - LAM supports set metadata in high bits 62:57 (LAM_U57) of a user
>    pointer, pass the pointer to SYSCALL, SYSCALL can dereference the
>    pointer and return correct result.

Is this test expected to pass?

I've tried to compile the Fedora kernel (6.15.9-201.fc42) with address
masking and LAM enabled, and while basic LAM support is there (the CPU
ignores the metadata bits after the arch_prctl system call), it's not
valid to use addresses with metadata in system calls:

$ ./lam_64 -t 8
not ok 1 SYSCALL: LAM_U57. syscall with metadata
ok 2 SYSCALL:[Negative] Disable LAM. Dereferencing pointer with metadata.
not ok 3 GET_USER: get_user() and pass a properly tagged user pointer.
ok 4 GET_USER:[Negative] get_user() with a kernel pointer and the top bit cleared.
ok 5 GET_USER:[Negative] get_user() with a kernel pointer and the bottom sign-extension bit cleared.
ok 6 GET_USER:[Negative] get_user() and pass a kernel pointer.
1..6
# Totals: pass:4 fail:2 xfail:0 xpass:0 skip:0 error:0

This also happens outside the test, where write (for example) returns
EFAULT if passed an address with metadata.

Thanks,
Florian