linux-kernel - [RFC 06/14] fork: zero vmap stack using clear

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Date: Mon, 11 Mar 2024 16:46:30 +0000
From: Pasha Tatashin <pasha.tatashin@...een.com>
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Subject: [RFC 06/14] fork: zero vmap stack using clear_page() instead of memset()

In preporation for dynamic kernel stacks do not zero the whole span of
the stack, but instead only the pages that are part of the vm_area.

This is because with dynamic stacks we might have only partially
populated stacks.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 kernel/fork.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 6a2f2c85e09f..41e0baee79d2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -263,8 +263,8 @@ static int memcg_charge_kernel_stack(struct vm_struct *vm)
 static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 {
 	struct vm_struct *vm_area;
+	int i, j, nr_pages;
 	void *stack;
-	int i;
 
 	for (i = 0; i < NR_CACHED_STACKS; i++) {
 		vm_area = this_cpu_xchg(cached_stacks[i], NULL);
@@ -282,7 +282,9 @@ 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. */
-		memset(stack, 0, THREAD_SIZE);
+		nr_pages = vm_area->nr_pages;
+		for (j = 0; j < nr_pages; j++)
+			clear_page(page_address(vm_area->pages[j]));
 
 		tsk->stack_vm_area = vm_area;
 		tsk->stack = stack;
-- 
2.44.0.278.ge034bb2e1d-goog