From:   andrey.konovalov@linux.dev
To:     Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Peter Collingbourne <pcc@google.com>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        kasan-dev@googlegroups.com,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        Evgenii Stepanov <eugenis@google.com>,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH 21/31] kasan, fork: don't tag stacks allocated with vmalloc
Date:   Tue, 30 Nov 2021 23:07:06 +0100
Message-Id: <4fbc6668845e699bf708aee5c11ad9fd012d4dcd.1638308023.git.andreyknvl@google.com>
In-Reply-To: <cover.1638308023.git.andreyknvl@google.com>
References: <cover.1638308023.git.andreyknvl@google.com>
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From: Andrey Konovalov <andreyknvl@google.com>

Once tag-based KASAN modes start tagging vmalloc() allocations,
kernel stacks will start getting tagged if CONFIG_VMAP_STACK is enabled.

Reset the tag of kernel stack pointers after allocation.

For SW_TAGS KASAN, when CONFIG_KASAN_STACK is enabled, the
instrumentation can't handle the sp register being tagged.

For HW_TAGS KASAN, there's no instrumentation-related issues. However,
the impact of having a tagged SP pointer needs to be properly evaluated,
so keep it non-tagged for now.

Note, that the memory for the stack allocation still gets tagged to
catch vmalloc-into-stack out-of-bounds accesses.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 kernel/fork.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index 3244cc56b697..062d1484ef42 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -253,6 +253,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 	 * so cache the vm_struct.
 	 */
 	if (stack) {
+		stack = kasan_reset_tag(stack);
 		tsk->stack_vm_area = find_vm_area(stack);
 		tsk->stack = stack;
 	}
-- 
2.25.1