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[81.44.253.244]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e3ecd8c05sm37044493f8f.49.2026.10.28.08.43.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Oct 2026 08:44:00 -0700 (PDT) From: =?UTF-8?q?Iv=C3=A1n=20Ezequiel=20Rodriguez?= To: Catalin Marinas , Will Deacon , Paul Walmsley , Palmer Dabbelt , linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org Cc: linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Mark Rutland , Mark Brown , Deepak Gupta , Alexandre Ghiti , Albert Ou , Shuah Khan , Christian Brauner , James Morse , Yury Khrustalev , Thiago Jung Bauermann , Samuel Holland , Zong Li , Charlie Jenkins , Shaopeng Tan , Zishun Yi , "Peter Zijlstra (Intel)" , stable@vger.kernel.org Subject: [PATCH v3 1/4] arm64/gcs: release GCS on failed fork Date: Wed, 28 Oct 2026 12:43:12 -0300 Message-ID: <20261028154315.1272705-2-ivanrwcm25@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261028154315.1272705-1-ivanrwcm25@gmail.com> References: <20261028154315.1272705-1-ivanrwcm25@gmail.com> X-Mailing-List: linux-kernel@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() can map a CLONE_VM GCS and still return 0. A later copy_process() failure calls exit_thread(), but arm64 did not implement it, so the VMA stayed in the parent's mm. Wire HAVE_EXIT_THREAD to gcs_free(). x86 already does this via exit_thread() -> shstk_free(). The separate x86 TLS leak is different: copy_thread() itself fails after the alloc, so copy_process() skips exit_thread(). args->fn tasks inherit GCS tracking without allocating; clear it so a failed CLONE_VM copy_process() cannot gcs_free() the caller's stack. Keep that helper in process.c with the other fork helpers. Fixes: 506496bcbb42 ("arm64/gcs: Ensure that new threads have a GCS") Cc: stable@vger.kernel.org Cc: Mark Brown Assisted-by: LLM Signed-off-by: Iván Ezequiel Rodriguez --- arch/arm64/Kconfig | 1 + arch/arm64/kernel/process.c | 16 ++++++++++++++++ 2 files changed, 17 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index cfef22aee709..3010ced4b4f2 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -177,6 +177,7 @@ config ARM64 select HAVE_ARM_SMCCC select HAVE_ASM_MODVERSIONS select HAVE_EBPF_JIT + select HAVE_EXIT_THREAD select HAVE_C_RECORDMCOUNT select HAVE_CMPXCHG_DOUBLE select HAVE_CMPXCHG_LOCAL diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 581f80e9b9b7..d17172e60acb 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -320,6 +320,13 @@ static int copy_thread_gcs(struct task_struct *p, return 0; } +static void gcs_reset_thread(struct task_struct *task) +{ + task->thread.gcs_base = 0; + task->thread.gcs_size = 0; + task->thread.gcspr_el0 = 0; +} + #else static void flush_gcs(void) { } @@ -328,6 +335,7 @@ static int copy_thread_gcs(struct task_struct *p, { return 0; } +static void gcs_reset_thread(struct task_struct *task) { } #endif @@ -341,6 +349,12 @@ void flush_thread(void) flush_gcs(); } +void exit_thread(struct task_struct *tsk) +{ + /* Failed fork after copy_thread(); deactivate_mm() does not run. */ + gcs_free(tsk); +} + void arch_release_task_struct(struct task_struct *tsk) { fpsimd_release_task(tsk); @@ -503,6 +517,8 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) p->thread.cpu_context.x19 = (unsigned long)args->fn; p->thread.cpu_context.x20 = (unsigned long)args->fn_arg; + /* No user GCS alloc here; drop inherited tracking for CLONE_VM. */ + gcs_reset_thread(p); if (system_supports_poe()) p->thread.por_el0 = POR_EL0_INIT; -- 2.43.0