linux-kernel - [PATCH v2 0/3] Noinstr fixes for K[CA]SAN with GCOV

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-next>] [day] [month] [year] [list]

Message-ID: <20251215-gcov-inline-noinstr-v2-0-6f100b94fa99@google.com>
Date: Mon, 15 Dec 2025 10:12:38 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, 
	Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Vincenzo Frascino <vincenzo.frascino@....com>, Marco Elver <elver@...gle.com>, 
	Ard Biesheuvel <ardb@...nel.org>
Cc: kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, 
	Brendan Jackman <jackmanb@...gle.com>
Subject: [PATCH v2 0/3] Noinstr fixes for K[CA]SAN with GCOV

Details:

 - ❯❯  clang --version
   Debian clang version 19.1.7 (3+build5)
   Target: x86_64-pc-linux-gnu
   Thread model: posix
   InstalledDir: /usr/lib/llvm-19/bin

 - Kernel config:

   https://gist.githubusercontent.com/bjackman/bbfdf4ec2e1dfd0e18657174f0537e2c/raw/a88dcc6567d14c69445e7928a7d5dfc23ca9f619/gistfile0.txt

Note I also get this error:

vmlinux.o: warning: objtool: set_ftrace_ops_ro+0x3b: relocation to !ENDBR: machine_kexec_prepare+0x810

That one's a total mystery to me. I guess it's better to "fix" the SEV
one independently rather than waiting until I know how to fix them both.

Note I also mentioned other similar errors in [0]. Those errors don't
exist in Linus' master and I didn't note down where I saw them. Either
they have since been fixed, or I observed them in Google's internal
codebase where they were instroduced downstream.

As discussed in [2], the GCOV+*SAN issue is attacked from two angles:
both adding __always_inline to the instrumentation helpers AND disabling
GCOV for noinstr.c. Only one or the other of these things is needed to
make the build error go away, but they both make sense in their own
right and both may serve to prevent other similar errors from cropping
up in future.

Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
Changes in v2:
- Also disable GCOV for noinstr.c (i.e. squash in [0]).
- Link to v1: [2] 

[0] https://lore.kernel.org/all/DERNCQGNRITE.139O331ACPKZ9@google.com/
[1] https://lore.kernel.org/all/20251117-b4-sev-gcov-objtool-v1-1-54f7790d54df@google.com/
[2] https://lore.kernel.org/r/20251208-gcov-inline-noinstr-v1-0-623c48ca5714@google.com

---
Brendan Jackman (3):
      kasan: mark !__SANITIZE_ADDRESS__ stubs __always_inline
      kcsan: mark !__SANITIZE_THREAD__ stub __always_inline
      x86/sev: Disable GCOV on noinstr object

 arch/x86/coco/sev/Makefile   | 2 ++
 include/linux/kasan-checks.h | 4 ++--
 include/linux/kcsan-checks.h | 2 +-
 3 files changed, 5 insertions(+), 3 deletions(-)
---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20251208-gcov-inline-noinstr-1550cfee445c

Best regards,
-- 
Brendan Jackman <jackmanb@...gle.com>