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([181.229.23.179]) by smtp.gmail.com with ESMTPSA id 71dfb90a1353d-5ec13f2cfe0sm456271e0c.14.2026.10.22.15.17.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Oct 2026 15:17:28 -0700 (PDT) From: =?UTF-8?q?Iv=C3=A1n=20Ezequiel=20Rodriguez?= To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org Cc: "H . Peter Anvin" , Shuah Khan , Christian Brauner , Rick Edgecombe , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, =?UTF-8?q?Iv=C3=A1n=20Ezequiel=20Rodriguez?= Subject: [PATCH v2 0/2] x86/shstk: don't leak a shadow stack when clone TLS fails Date: Thu, 22 Oct 2026 19:17:19 -0300 Message-ID: <20261022221722.619233-1-ivanrwcm25@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261015023147.519257-1-ivanrwcm25@gmail.com> References: <20261015023147.519257-1-ivanrwcm25@gmail.com> X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit copy_thread() maps a shadow stack and set_new_tls() can still fail. That error goes to bad_fork_cleanup_io and skips exit_thread(). bad_fork_cleanup_thread calls exit_thread() only after copy_thread() has returned 0. commit 748c90c69336 ("x86/shstk: Remove useless clone error handling") removed the shstk_free() on the set_new_tls() failure. Restoring it only there puts back the single free. The allocation-error return still aliases the parent, and the exit_thread() path is left alone, so the double unmap that commit avoided does not come back. The selftest uses kselftest.h / KTAP. Feature and clone3 availability skips run before ksft_set_plan(). Missing /proc/self/smaps is SKIP. Read errors, truncated smaps lines, and a VMA range without VmFlags are FAIL. A valid-TLS clone3 must succeed before EPERM on a bad TLS counts as the leak path; ENOSYS/EPERM/EACCES SKIP that control. Regression (CONFIG_X86_USER_SHADOW_STACK=y, host and one-vCPU KVM -cpu host,migratable=off): Scenario Without fix With fix 16 bad-TLS clone3 +16 ss VMAs +0 ss VMAs Parent shadow stack kept + call/ret OK kept + call/ret OK KTAP 2/3 (test 3 fail) 3/3 pass Changes in v2: - Nest the TLS error check under CLONE_SETTLS, as suggested by Rick Edgecombe. - Use a dedicated shadow-stack cleanup label. - Return zero explicitly on the successful path. - Remove the redundant cleanup comment. - Selftest: rewrite on kselftest.h / KTAP (plan 3). Fix RDSSPQ comment; align get_ssp() with test_shadow_stack; SKIP only ENOSYS/EPERM/EACCES on the valid-TLS control; FAIL on truncated or incomplete smaps records that would under-count ss VMAs. Link: https://lore.kernel.org/lkml/20261015023147.519257-1-ivanrwcm25@gmail.com/ Iván Ezequiel Rodriguez (2): x86/shstk: free shadow stack when copy_thread() fails selftests/x86: shadow stack must survive a bad TLS arch/x86/kernel/process.c | 13 +- tools/testing/selftests/x86/Makefile | 3 +- tools/testing/selftests/x86/shstk_clone_tls.c | 334 ++++++++++++++++++ 3 files changed, 346 insertions(+), 4 deletions(-) create mode 100644 tools/testing/selftests/x86/shstk_clone_tls.c -- 2.43.0