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Mon, 28 Sep 2026 10:41:49 -0700 (PDT) Date: Mon, 28 Sep 2026 17:41:09 +0000 In-Reply-To: <20260928174122.3380703-1-smostafa@google.com> Mime-Version: 1.0 References: <20260928174122.3380703-1-smostafa@google.com> X-Mailer: git-send-email 2.56.0.rc1.315.gc6ed9934b7-goog Message-ID: <20260928174122.3380703-3-smostafa@google.com> Subject: [RFC PATCH 02/15] fork: Don't assume fully populated stack during reuse From: Mostafa Saleh To: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-hardening@vger.kernel.org, linux-rt-devel@lists.linux.dev Cc: corbet@lwn.net, skhan@linuxfoundation.org, rdunlap@infradead.org, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, akpm@linux-foundation.org, urezki@gmail.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, kees@kernel.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, gustavoars@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, David Stevens , Mostafa Saleh Content-Type: text/plain; charset="UTF-8" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260928_104152_362521_F1F716C3 X-CRM114-Status: GOOD ( 14.83 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: David Stevens In preparation for partially populated kernel stacks, don't assume that vm_area->nr_pages matches THREAD_SIZE when clearing a stack for reuse. Note that the VA range is still THREAD_SIZE in that case but it might not be fully allocated. Signed-off-by: David Stevens [Resolve conflict and updated commit msg] Signed-off-by: Mostafa Saleh --- kernel/fork.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index 2065693e762c..ec4431bf309a 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -335,11 +335,16 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node) vm_area = alloc_thread_stack_node_from_cache(tsk, node); if (vm_area) { + unsigned long offset = 0; + if (memcg_charge_kernel_stack(vm_area)) { vfree(vm_area->addr); return -ENOMEM; } + if (!IS_ENABLED(CONFIG_STACK_GROWSUP)) + offset = THREAD_SIZE - vm_area->nr_pages * PAGE_SIZE; + /* Reset stack metadata. */ if (!kasan_hw_tags_enabled()) kasan_unpoison_range(vm_area->addr, THREAD_SIZE); @@ -347,7 +352,7 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node) stack = kasan_reset_tag(vm_area->addr); /* Clear stale pointers from reused stack. */ - clear_pages(vm_area->addr, vm_area->nr_pages); + clear_pages(vm_area->addr + offset, vm_area->nr_pages); tsk->stack_vm_area = vm_area; tsk->stack = stack; -- 2.56.0.rc1.315.gc6ed9934b7-goog